Pro- and anti-inflammatory cytokine expression in carp blood and head kidney leukocytes exposed to cyanotoxin stress--an in vitro study

Liposome encapsulating pine bark extract in Nile tilapia: Targeting interrelated immune and antioxidant defense to combat coinfection with Aeromonas hydrophila and Enterococcus faecalis

Application of smart delivery systems for encapsulation of natural ingredients provides novel avenues and is being frequently developed. Thus, we aimed to highlight the effects of cyclosome liposomal pine bark extract (CL-PBE) on Nile tilapia growth, immunomodulation, antioxidant capacity and resistance against coinfection with Aeromonas hydrophila and Enterococcus faecalis and their associated virulence genes. The experiment was conducted on four fish groups receiving a control diet (control) along with three baseline meals supplemented with 200, 400 and 600 mg/kg diet of CL-PBE (CL-PBE 200, 400 and 600, respectively). At the end of the 12-weeks feeding trial, the tilapias were intraperitoneally challenged with virulent A. hydrophila strain and five days later, E. faecalis challenge was carried out. The results revealed that tilapias fed diets fortified with CL-PBE displayed significantly enhanced growth rate and feed conversion ratio in a dose-dependent manner. Moreover, we demonstrated that CL-PBE had potent antioxidant property presented by modulation of several markers of oxidative stress; substantial reductions in reactive oxygen species, hydrogen peroxide and malondialdehyde levels, an elevation in total antioxidant capacity and boosting glutathione peroxidase (GSH-Px), catalase (CAT) and superoxide dismutase (SOD) activities in fish serum and muscle tissues. This was also correlated with augmenting the expression of CAT, SOD, GSH-Px, Nrf2 and caspase-1 genes alongside reducing those of COX-2, HSP70 and iNOS genes in response to CL-PBE. Our data demonstrated that CL-PBE fortification counteracted the overly pronounced inflammatory response-mediated induction of IL-1β, TNF-α, MHCII and TLR2 genes at the transcriptional levels post coinfection together with promotion in MUC2 and IL-10 genes expression. Notably, our findings displayed optimal well-functioning fish immune system post dietary supplementation of CL-PBE for the protection against coinfection with A. hydrophila and E. faecalis. This was evident from the decline of their counts and hence encompassing the capacity to reduce cumulative mortality percentage in conjunction with interference with their virulence via the significant downregulatory effects of CL-PBE on E. faecalis esp and gelE and A. hydrophila act and fla virulence genes. Taken together, our study strongly suggested dietary inclusion of CL-PBE for Nile tilapias with superior growth performance and significant economic benefits coupled with potent stimulatory effects on antioxidant capacity and immune response expediting our detailed understanding of how coinfection with A. hydrophila and E. faecalis was controlled.

Effects of Dietary Fish Oil Supplementation on the Growth, Proximate Composition, and Liver Health of Chinese Stripe-Necked Turtle (Mauremys sinensis)

Dietary lipids provide energy for animals and can also be converted into other nutrients (such as non-essential amino acids), which play a role in saving protein. The Chinese stripe-necked turtle is a protected and endangered species that has been bred in captivity; however, basic data on lipid requirements remain unavailable. In this study, 360 Mauremys sinensis (body weight of 65.32 ± 0.15 g) were randomly divided into six groups with three replicates per group; the turtles were fed experimental diets supplemented with various levels of fish oil (i.e., 1% (control group, CG), 3.5% (HF-1), 6% (HF-2), 8.5% (HF-3), 11% (HF-4), and 13.5% (HF-5)) for 10 weeks. The results showed that compared with CG, increasing the fish oil level promoted the growth performance of turtles, and the HF-3 group achieved the best effect. The HF-4 group showed the highest increases in the hepatosomatic index and viscerosomatic index. In addition, increased lipid levels also increased the crude lipid content and reduced the crude protein content in muscle tissue. Oil red O staining showed that the liver lipid content increased with the level of supplemented fish oil, which is consistent with the results of the hepatosomatic index. Compared with CG, triglyceride, total cholesterol, and low-density lipoprotein cholesterol increased significantly in both the liver and serum when fish oil levels exceeded 8.5% (p < 0.05), while high-density lipoprotein cholesterol decreased significantly. Aspartate transaminase and cerealthirdtransaminase levels in serum increased significantly when fish oil levels exceeded 8.5% (p < 0.05). Moreover, the activities of antioxidant enzymes (GSH-Px, SOD, T-AOC, and CAT) and MDA showed similar results, indicating that high fish oil levels (8.5-13.5%) caused liver tissue damage in M. sinensis. Increased fish oil levels significantly upregulated the expression levels of cytokines (IFN-γ, TNF-α, TGF-β1, IL-10, and IL-12) (p < 0.05), downregulated the expression levels of antioxidant enzyme-related genes (cat, mn-sod, and gsh-px), and increased apoptosis of liver cells. Supplementation of the diet with 3.5-6% fish oil improved the growth performance of M. sinensis, and the turtles maintained a beneficial immune status. The results provide a scientific basis for optimizing the commercial feed formula of M. sinensis.

Microcystin-LR improves anti-tumor efficacy of oxaliplatin through induction of M1 macrophage polarization

Tumor-associated macrophages within the tumor microenvironment play an immunosuppressive role by promoting tumor growth and immune evasion. Macrophages are highly plastic and can be stimulated to adopt an anti-tumor M1 phenotype. In this study, we used microcystin-LR (MC-LR), a cyclic heptapeptide produced by cyanobacteria, to induce in vitro macrophage innate immunity and transition into the anti-tumor M1 phenotype. MC-LR was also tested in vivo in a mouse model of colorectal cancer. An intraperitoneal injection of MC-LR increased the proportion of CD86⁺ M1 macrophages and triggered the maturation of CD11c⁺ dendritic cells within tumor tissues. MC-LR combined with the chemotherapeutic drug oxaliplatin significantly inhibited tumor growth in vivo. Flow cytometry analysis revealed increased infiltration of activated cytotoxic (CD8⁺, PD-1⁺) T-cells and anti-tumor cytokines (IFNγ and Granzyme B) in the tumor tissues of the combination therapy group, suggesting that this may be the primary mechanism behind the anti-tumor effect of the combination treatment. These findings indicate that MC-LR regulates the immune stimulation of macrophage polarization and dendritic cell maturation, effectively reversing tumor immunosuppression, activating an anti-tumor immune response, and enhancing tumor therapy.

Rhodiola rosea L. improved intestinal digestive enzyme activities, inflammatory response, barrier and microbiota dysbiosis in Lateolabrax maculatus juveniles fed with high-carbohydrate diets

A 56-d feeding trial was conducted to evaluate the influences of Rhodiola rosea L. on digestive enzyme activities, intestinal barrier, inflammatory response, and microbiota dysbiosis in Lateolabrax maculatus juveniles (9.37 ± 0.03 g) fed with high-carbohydrate diets. Six diets were designed: a control diet (20% corn starch, Control), high-carbohydrate diet (30% corn starch, HC1), and four high-carbohydrate diets supplemented with Rhodiola rosea L. at 30, 60, 90 and 120 mg/kg (HC2, HC3, HC4 and HC5, respectively). Compared with the control group, the HC1 diet remarkably increased α-amylase, lipase, and chymotrypsin activities in the intestine (p < 0.05), as well as the mRNA levels of Claudin-15, NF-κB, TNF-α, IL-1β, and IL-8 (p < 0.05) and the relative abundance of Proteobacteria and Photobacterium in the intestine, which belong to the phylum and genus level, respectively. But the opposite trend was found in muscular thickness and villus lengths (p < 0.05), the mRNA levels of Occludin, ZO-1, and TGF-β (p < 0.05), at the level of phylum and genus level in the HC1 group, and the relative abundance of Firmicutes, Bacteroidetes, and Bacillus in the intestine compared with the control group. Intestinal chymotrypsin activity was significantly higher in the HC3 group and intestinal muscular thickness and villus lengths were also significantly higher in the HC2, HC3, HC4, and HC5 groups compared to the HC1 group (p < 0.05). In addition, Occludin mRNA expression in the intestine was significantly increased in the HC2, HC4, and HC5 groups compared to the HC1 group. ZO-1 and TGF-β mRNA expression in the intestine were significantly increased in the HC2, HC3, HC4, and HC5 groups compared to the HC1 group (p < 0.05). At the phylum level, the relative abundance of Firmicutes and Bacteroidetes was higher in the intestine in the HC2, HC3, HC4, and HC5 groups than that in the HC1 group. On the contrary, intestinal lipase and chymotrypsin activities were significantly decreased in the HC2 group compared to the HC1 group, respectively (p < 0.05). The Claudin-15, NF-κB, TNF-α, IL-1β, and IL-8 mRNA expression in the intestine were significantly decreased in the HC2, HC3, HC4, and HC5 groups compared to the HC1 group (p < 0.05). Besides, at the genus level, compared to the HC1 group, the relative abundance of Photobacterium in the intestine and the diversity of the intestinal microbiota in the HC2, HC3, HC4, and HC5 groups were all decreased. In conclusion, these results demonstrated that the addition of Rhodiola rosea L. in high-carbohydrate diets can improve intestinal digestive enzyme activities, inflammatory response and intestinal barrier-related gene expression, and microbiota dysbiosis in L. maculatus. The suitable supplemental level of Rhodiola rosea L. in high-carbohydrate diets of L. maculatus is 60 mg/kg.

The two-way immunotoxicity in native fish induced by exudates of Microcystis aeruginosa: Immunostimulation and immunosuppression

Secondary metabolites of cyanobacterial blooms have caused serious risks to aquatic animals. The immune system is an important barrier for fish against pollutants in aquatic systems. The immunetoxic mechanism of the exudates of Microcystis aeruginosa (MaE) on fish was lacking due to the complex components of MaE. In this project, Sinocyclocheilus grahami was used as the model to study the immunotoxic effects of MaE and PHS (one of the main components of the MaE) in fish. The immunosuppression effects of MaE are mainly in, decreased head-kindey index, damaged tissue structure of head-kidney and downregulated NF-κB, IL-1β. PHS induce immunostimulation via, increasing spleen index, apparently increasing leucocytes, increasing the IgM and lysozyme levels in serum and skin mucus, upregulating protease in skin mucus, increasing pro-immunologic factors (IL-1β, IL-6, IL-8, IL-10, TNF-α and NF-κB), probably activating the TLRs/NF-κB, MAPK, FoxO1 and PPARγ signaling pathways. Therefore, our research identified potential data gaps that how the exudates of cyanobacteria induces immunostimulation and immunosuppression from immune organs level to skin mucus to blood cells to inflammatory factors to potential molecular initiating event of MaE and PHS. Further research is needed to obtain a deeper view of the molecular mechanisms involved in MaE and PHS immunotoxicity and its consequences in long-time exposures.

Environmental impacts of chlorpyrifos: Transgenerational toxic effects on aquatic organisms cannot be ignored

Chlorpyrifos (CPF) has been extensively used in the world and frequently found in natural environments, might cause a range of environmental issues and pose a health risk to aquatic species. However, investigation of its toxic effects on offspring after parental exposure has been neglected, especially for aquatic organisms such as fish. In the current study, the effects of chronic CPF exposure (3 and 60 μg/L) on adult zebrafish (F0) was investigated to determine its influence on adult reproductive capacity and offspring (F1 and F2). The results showed the existence of CPF both in F0 ovaries and F1 embryos and larvae, indicating that CPF could be transferred directly from the F0 adult fish to F1 offspring. After 90 d exposure, we observed that F0 female fish showed increased proportion of perinucleolar oocyte in the ovaries, decreased proportion of mature oocyte, and decreased egg production, but not in F1 adult. The transcriptomic analysis revealed that the disruption of metabolism during oocyte maturation in the CPF treatment zebrafish might interfere with F0 oocytes development and quality and ultimately influence offspring survival. For the larvae, the parental CPF exposure distinctly inhibited heart rate at 72 and 120 hpf and increased the mortality of F1 but not F2 larvae. The changes of biochemical indicators confirmed a disturbance in the oxidative balance, induced inflammatory reaction and apoptosis in F1 larvae. Furthermore, the changing profiles of mRNA revealed by RNA-seq confirmed an increased susceptibility in F1 larvae and figured out potential disruptions of ROS metabolism, immune system, apoptosis, and metabolism pathways. Taken together, these results show that chronic CPF treatment can induce reproductive toxicity, and parental transfer of CPF occurs in fish, resulting in transgenerational alters in F1 generation survival and transcription that raising concerns on the ecological risk of CPF in the natural environment.

Excessive dietary soluble arabinoxylan impairs the intestinal physical and immunological barriers via activating MAPK/NF-κB signaling pathway in rainbow trout (Oncorhynchus mykiss)

Arabinoxylan (AX) has been deemed as an antinutritional factor, but limited information has addressed the effects of dietary AX on intestinal health of fish. The present study investigated the effects of dietary AX on intestinal mucosal physical and immunological barriers of rainbow trout (Oncorhynchus mykiss). Five isoproteic and isolipidic experimental diets (AXE, AX0, AX2.5, AX5 and AX10) were formulated to contain 0.03% arabinoxylanase as well as 0%, 2.5%, 5% and 10% AX, respectively. Each diet was randomly distributed to triplicate groups of 35 juvenile (average weight 3.14 ± 0.02 g) per tank in a rearing system maintained at 17 ± 1 °C for 9 weeks. Dietary AX supplementation regardless of inclusion levels significantly (P < 0.05) depressed the growth performance and feed utilization. The plasma endothelin-1 and d-lactic acid contents as well as diamino oxidase activity were significantly higher in fish fed diet AX10 compared to fish fed diet AX0. Dietary inclusion of 5-10% AX resulted in decreased intestinal villus height, goblet cell number and desmosome density, increased crypt depth, short and irregular microvilli, widened intercellular space; down-regulated the mRNA levels of occludin in hindgut, claudin3 and ZO-1 in foregut and midgut, but up-regulated the mRNA levels of claudin12 and claudin15 in midgut as well as claudin23 in foregut, midgut and hindgut. Furthermore, dietary 5-10% AX supplementation decreased the midgut and hindgut complement 3, complement 4 and sIgT contents as well as the midgut IgM and hindgut IL-10 contents. Conversely, the hindgut TNF-α and IL-6 contents increased with the rising dietary AX level. RT-qPCR demonstrated that the pro-inflammatory cytokines (IL-1β, IL-6, IL-8, IL-12β, IFN-γ, and TNF-α) and pIgR mRNA levels in midgut and hindgut were up-regulated by dietary AX inclusion of 5-10% AX. Meanwhile, the mRNA levels of p38 MAPK, IκBα, and NF-κB p65 in midgut and hindgut raised gradually with the increasing dietary AX content. The Western blot results showed that the protein expression levels of p38 MAPK and NF-κB generally increased with the rising dietary AX content. Dietary treatment with 0.03% arabinoxylanase did not affect the growth performance and intestinal health of rainbow trout (P > 0.05). In conclusion, excessive dietary AX inclusion (5-10%) increased the intestinal permeability and induced the intestinal inflammatory response via activating MAPK/NF-κB signaling pathway, and ultimately damaged the intestinal barrier function of rainbow trout.

Immuno-physiological effects of dietary reishi mushroom powder as a source of beta-glucan on Rohu, Labeo rohita challenged with Aeromonas veronii

Beta-glucans have immense potential to stimulate immune modulation in fish by being injected intramuscularly, supplemented with feed or immersion routes of administration. We studied how supplementing Labeo rohita's diet with reishi mushroom powder containing beta-glucan influenced immunological function. A supplemented diet containing 10% reishi mushroom powder was administered for 120 days. Afterwards, analyses were conducted on different immunological parameters such as antioxidants, respiratory burst, reactive oxygen species (ROS), alternative complement activity, and serum immunoglobulin, which resulted significant increases (p < 0.05; p < 0.01) for the reishi mushroom-fed immune primed L. rohita. Additionally, analyzing various hematological parameters such as erythrocytes and leukocytes count were assessed to elucidate the immunomodulatory effects, indicating positive effects of dietary reishi mushroom powder on overall fish health. Furthermore, the bacterial challenge-test with 1.92 × 104 CFU/ml intramuscular dose of Aeromonas veronii showed enhanced disease-defending system as total serum protein and lysozyme activity levels accelerated significantly (p < 0.01). Nevertheless, reishi mushroom powder contained with beta-glucan ameliorated the stress indicating parameters like acetylcholinesterase (AChE), serum-glutamic pyruvic transaminase (SGPT) and serum-glutamic oxaloacetic transaminase (SGOT) enzyme activities results suggested the fish's physiology was unaffected. Therefore, the results indicated that adding dietary reishi mushroom as a source of beta-glucan could significantly boost the immune responses in Rohu.

In vivo antibacterial activity of medicinal plant Sophora flavescens against Streptococcus agalactiae infection

Streptococcosis disease caused by Streptococcus agalactiae (Group B Streptococcus, GBS) results in a huge economic loss of tilapia culture. It is urgent to find new antimicrobial agents against streptococcosis. In this study, 20 medicinal plants were evaluated in vitro and in vivo to obtain medicinal plants and potential bioactive compounds against GBS infection. The results showed that the ethanol extracts of 20 medicinal plants had low or no antibacterial properties in vitro, with a minimal inhibitory concentration ≥256 mg/L. Interestingly, in vivo tests showed that 7 medicinal plants could significantly inhibit GBS infection in tilapia, and Sophora flavescens (SF) had the strongest anti-GBS activity in tilapia, reaching 92.68%. SF could significantly reduce the bacterial loads of GBS in different tissues (liver, spleen and brain) of tilapia after treated with different tested concentrations (12.5, 25.0, 50.0 and 100.0 mg/kg) for 24 h. Moreover, 50 mg/kg SF could significantly improve the survival rate of GBS-infected tilapia by inhibiting GBS replication. Furthermore, the expression of antioxidant gene cat, immune-related gene c-type lysozyme and anti-inflammatory cytokine il-10 in liver tissue of GBS-infected tilapia significantly increased after treated with SF for 24 h. Meanwhile, SF significantly reduced the expression of immune-related gene myd88 and pro-inflammatory cytokines il-8 and il-1β in liver tissue of GBS-infected tilapia. The negative and positive models of UPLC-QE-MS, respectively, identified 27 and 57 components of SF. The major components of SF extract in the negative model were α, α-trehalose, DL-malic acid, D- (-)-fructose and xanthohumol, while in the positive model were oxymatrine, formononetin, (-)-maackiain and xanthohumol. Interestingly, oxymatrine and xanthohumol could significantly inhibit GBS infection in tilapia. Taken together, these results suggest that SF can inhibit GBS infection in tilapia, and it has potential for the development of anti-GBS agents.

Dietary Supplementation of Chlorella vulgaris Effectively Enhanced the Intestinal Antioxidant Capacity and Immune Status of Micropterus salmoides

An M. salmoides fish meal diet was supplemented with 0 (CHL0, Control), 38 (CHL38), 76 (CHL76), 114 (CHL114), and 152 (CHL152) mg/kg C. vulgaris for 60 days, and their serum and intestinal samples were analyzed. The results showed that the albumin (ALB) and total protein (TP) contents were observably enhanced in the CHL76 group compared with the Control group. The intestinal glutathione (GSH) and glutathione peroxidase (GSH-Px) contents were enhanced significantly in the CHL76 group, while the total antioxidant capacity (T-AOC) was enhanced in the CHL38 group, compared with the Control group. However, supplementation of >76 g/kg C. vulgaris significantly inhibited the superoxide dismutase (SOD) activity in the intestines of M. salmoides. Moreover, the malondialdehyde (MDA) content was observably dropped in the CHL-supplemented groups compared with the Control group. Transcriptome analysis of the CHL76 and Control groups displayed a total of 1384 differentially expressed genes (DEGs). KEGG analysis revealed that these DEGs were enriched in apoptosis, cytokine-cytokine receptor interaction, tight junction (TJ), and phagosome signaling pathways, which were associated with improved intestinal immunity in the CHL76 group. Additionally, the DEGs enriched in the above pathways were also correlated with the antioxidant parameters, such as catalase (CAT), GSH, GSH-Px, SOD, T-AOC, and MDA. Therefore, our study found that dietary supplementation of C. vulgaris effectively enhanced the intestinal antioxidant capacity of M. salmoides by increasing antioxidant enzyme activity and decreasing MDA content. Additionally, dietary supplementation of C. vulgaris improved the intestinal immune status of M. salmoides by reducing proapoptotic and proinflammatory factors, increasing intestinal TJs- and phagosome-related genes expressions, and increasing the serum ALB and TP contents. Lastly, quadratic regression analysis of the serum biochemical indices (ALB and TP) and intestinal antioxidant parameters (GSH-Px and GSH) revealed that the optimal supplemental level of C. vulgaris in the M. salmoides diet was 58.25-77.7 g/kg.

In Vitro Mutagenic and Genotoxic Assessment of Anatoxin-a Alone and in Combination with Cylindrospermopsin

Anatoxin-a (ATX-a) is a cyanobacterial toxin whose occurrence has been reported worldwide and has attracted increasing scientific interest due to its toxicity. Moreover, in nature, ATX-a usually appears together with other cyanotoxins, such as cylindrospermopsin (CYN), so possible interaction phenomena could happen and should be considered for risk assessment purposes. For this reason, the aim of this work was to explore the potential mutagenicity and genotoxicity of pure ATX-a and an ATX-a/CYN mixture using a battery of in vitro assays, including the bacterial reverse-mutation assay in Salmonella typhimurium (OECD 471) and the micronucleus test (MN) (OECD 487) on L5178Y Tk+/- cells. The results showed that ATX-a was not mutagenic either alone or in combination with CYN under the conditions tested. Nevertheless, genotoxic effects were observed for both ATX-a and its mixture with CYN following the in vitro MN assay. The genotoxicity exhibited by ATX-a was only observed in the absence of S9 mix, whereas in the cyanotoxin mixture the concentration-dependent genotoxicity of ATX-a/CYN in vitro was observed only in the presence of S9. Thus, the toxicity induced by cyanotoxin mixtures may vary from that produced by toxins alone, and consequently more studies are necessary in order to perform more realistic risk assessments.

Acute toxic effects of microcystin-LR on crayfish (Procambarus clarkii): Insights from antioxidant system, histopathology and intestinal flora

To study the toxic effects of microcystin-LR (MC-LR) on crayfish, adult male Procambarus clarkii were exposed to different concentrations of MC-LR for 96 h. In the meantime, the accumulation characteristics of MC-LR and the alternations of antioxidant system, histopathology and intestinal flora of P. clarkii were investigated. The results demonstrated that the hepatopancreas, gills and intestines of P. clarkii could effectively accumulate MC-LR. Antioxidant-related genes such as Mn-sod, cat, gst, gpx, mt and hsp70 showed different expression trends in different organs to respond to MC-LR-induced oxidative stress. MC-LR led to histological changes in the hepatopancreas, gills and intestines, thus affecting their corresponding physiological functions. Additionally, the abundances of bacterial phyla including Firmicutes and Planctomycetes and genera including Dysgonomonas, Brevundimonas and Anaerorhabdus in the intestine were significantly changed after MC-LR exposure, and the disruption of intestinal flora might further cause abnormal intestinal microbial metabolism and genetics in P. clarkii. This study provides novel mechanistic insights into the toxic impacts of microcystins on aquatic crustaceans. HIGHLIGHTS: • MC-LR was significantly accumulated in the hepatopancreas, gills and intestines of P. clarkii. • MC-LR induced the differential expression of antioxidant-related genes of P. clarkii. • MC-LR caused histological alterations in the hepatopancreas, gills and intestines of P. clarkii. • MC-LR affected the intestinal microbial composition and function of P. clarkii.

A Review of Common Cyanotoxins and Their Effects on Fish

Global warming and human-induced eutrophication drive the occurrence of various cyanotoxins in aquatic environments. These metabolites reveal diversified mechanisms of action, encompassing cyto-, neuro-, hepato-, nephro-, and neurotoxicity, and pose a threat to aquatic biota and human health. In the present paper, we review data on the occurrence of the most studied cyanotoxins, microcystins, nodularins, cylindrospermopsin, anatoxins, and saxitoxins, in the aquatic environment, as well as their potential bioaccumulation and toxicity in fish. Microcystins are the most studied among all known cyanotoxins, although other toxic cyanobacterial metabolites are also commonly identified in aquatic environments and can reveal high toxicity in fish. Except for primary toxicity signs, cyanotoxins adversely affect the antioxidant system and anti-/pro-oxidant balance. Cyanotoxins also negatively impact the mitochondrial and endoplasmic reticulum by increasing intracellular reactive oxygen species. Furthermore, fish exposed to microcystins and cylindrospermopsin exhibit various immunomodulatory, inflammatory, and endocrine responses. Even though cyanotoxins exert a complex pressure on fish, numerous aspects are yet to be the subject of in-depth investigation. Metabolites other than microcystins should be studied more thoroughly to understand the long-term effects in fish and provide a robust background for monitoring and management actions.

Effects of dietary tryptophan on the antioxidant capacity and immune response associated with TOR and TLRs/MyD88/NF-κB signaling pathways in northern snakehead, Channa argus (Cantor, 1842)

Introduction

Dietary tryptophan (Trp) has been shown to influence fish feed intake, growth, immunity and inflammatory responses. The purpose of this study was to investigate the effect and mechanism of Trp on immune system of juvenile northern snakehead (Channa argus Cantor, 1842).

Methods

A total of 540 fish (10.21 ± 0.11 g) were fed six experimental diets containing graded levels of Trp at 1.9, 3.0, 3.9, 4.8, 5.9 and 6.8 g/kg diet for 70 days, respectively.

Results and Discussion

The results showed that supplementation of 1.9-4.8 g/kg Trp in diets had no effect on the hepatosomatic index (HSI) and renal index (RI), while dietary 3.9 and 4.8 g/kg Trp significantly increased spleen index (SI) of fish. Dietary 3.9, 4.8, 5.9 and 6.8 g/kg Trp enhanced the total hemocyte count (THC), the activities of total antioxidant capacity (T-AOC) and superoxide dismutase (SOD). Malondinaldehyde (MDA) levels in the blood were significantly decreased by consuming 3.9 and 4.8 g/kg Trp. Fish fed with 3.0 and 3.9 g/kg Trp diets up-regulated interleukin 6 (il-6) and interleukin 8 (il-8) mRNA levels. The expression of tumor necrosis factor α (tnf-α) was highest in fish fed with 3.0 g/kg Trp diet, and the expression of interleukin 1β (il-1β) was highest in fish fed with 3.9 g/kg Trp diet. Dietary 4.8, 5.9 and 6.8 g/kg Trp significantly decreased il-6 and tnf-α mRNA levels in the intestine. Moreover, Trp supplementation was also beneficial to the mRNA expression of interleukin 22 (il-22). Additionally, the mRNA expression levels of target of rapamycin (tor), toll-like receptor-2 (tlr2), toll-like receptor-4 (tlr4), toll-like receptor-5 (tlr5) and myeloid differentiation primary response 88 (myd88) of intestine were significantly up-regulated in fish fed 1.9, 3.0 and 3.9 g/kg Trp diets, and down-regulated in fish fed 4.8, 5.9 and 6.8 g/kg Trp diets. Dietary 4.8 and 5.9 g/kg Trp significantly increased the expression of inhibitor of nuclear factor kappa B kinase beta subunit (ikkβ) and decreased the expression of inhibitor of kappa B (iκbα), but inhibited nuclear transcription factor kappa B (nf-κb) mRNA level. Collectively, these results indicated that dietary 4.8 g/kg Trp could improve antioxidant capacity and alleviate intestinal inflammation associated with TOR and TLRs/MyD88/NF-κB signaling pathways.

Toxic Effects Produced by Anatoxin-a under Laboratory Conditions: A Review

The presence of cyanotoxins and its bioaccumulation in the food chain is an increasingly common problem worldwide. Despite the toxic effects produced by Anatoxin-a (ATX-a), this neurotoxin has been less studied compared to microcystins (MCs) and cylindrospermopsin (CYN). Studies conducted under laboratory conditions are of particular interest because these provide information which are directly related to the effects produced by the toxin. Currently, the World Health Organization (WHO) considers the ATX-a toxicological database inadequate to support the publication of a formal guideline reference value. Therefore, the aim of the present work is to compile all of the in vitro and in vivo toxicological studies performed so far and to identify potential data gaps. Results show that the number of reports is increasing in recent years. However, more in vitro studies are needed, mainly in standardized neuronal cell lines. Regarding in vivo studies, very few of them reflect conditions occurring in nature and further studies with longer periods of oral exposure would be of interest. Moreover, additional toxicological aspects of great interest such as mutagenicity, genotoxicity, immunotoxicity and alteration of hormonal balance need to be studied in depth.

Incorporating Microbial Species Interaction in Management of Freshwater Toxic Cyanobacteria: A Systems Science Challenge

Water resources are critically important, but also pose risks of exposure to toxic and pathogenic microbes. Increasingly, a concern is toxic cyanobacteria, which have been linked to the death and disease of humans, domesticated animals, and wildlife in freshwater systems worldwide. Management approaches successful at reducing cyanobacterial abundance and toxin production have tended to be short-term solutions applied on small scales (e.g., algaecide application) or solutions that entail difficult multifaceted investments (e.g., modification of landscape and land use to reduce nutrient inputs). However, implementation of these approaches can be undermined by microbial species interactions that (a) provide toxic cyanobacteria with protection against the method of control or (b) permit toxic cyanobacteria to be replaced by other significant microbial threats. Understanding these interactions is necessary to avoid such scenarios and can provide a framework for novel strategies to enhance freshwater resource management via systems science (e.g., pairing existing physical and chemical approaches against cyanobacteria with ecological strategies such as manipulation of natural enemies, targeting of facilitators, and reduction of benthic occupancy and recruitment). Here, we review pertinent examples of the interactions and highlight potential applications of what is known.

Fish Meal Replacement by Mixed Plant Protein in the Diets for Juvenile Yellow Catfish Pelteobagrus fulvidraco: Effects on Growth Performance and Health Status

Increasing dietary replacement levels of fish meal by alternative plant proteins are of value for aquaculture. Here, a 10-week feeding experiment was undertaken to explore the effects of fish meal replacement by mixed plant protein (at a 2 : 3 ratio of cottonseed meal to rapeseed meal) on growth performance, oxidative and inflammatory responses, and mTOR pathway of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (2.38 ± 0.1 g, mean ± SEM) were randomly divided into 15 indoors fiberglass tanks, 30 fish each tank, and fed five isonitrogenous (44% crude protein) and isolipidic (9% crude fat) diets with fish meal replaced by mixed plant protein at 0% (the control), 10% (RM10), 20% (RM20), 30% (RM30), and 40% (RM40), respectively. Among five groups, fish fed the control, and RM10 diets tended to have higher growth performance, higher protein content, and lower lipid content in livers. Dietary mixed plant protein substitute increased hepatic free gossypol content and damaged liver histology and reduced the serum total essential amino acids, total nonessential amino acids, and total amino acid contents. Yellow catfish fed the control, and RM10 diets tended to have higher antioxidant capacity. Dietary mixed plant protein replacement tended to promote proinflammatory responses and inhibited mTOR pathway. Based on the second regression analysis of SGR against mixed plant protein substitutes, the optimal replacement level of fish meal by mixed plant protein was 8.7%.

Exploring the Interactive Effects of Thymol and Thymoquinone: Moving towards an Enhanced Performance, Gross Margin, Immunity and Aeromonas sobria Resistance of Nile Tilapia (Oreochromis niloticus)

Plant-derived bioactive compounds with promising nutritional and therapeutic attributes (phytogenics) are among the top priorities in the aquaculture sector. Therefore, the impact of thymol (Thy) and/or thymoquinone (ThQ) on the growth, immune response antioxidant capacity, and Aeromonas sobria (A. sobria) resistance of Nile tilapia was investigated. Four fish groups were fed a control diet and three basal diets supplemented with 200 mg/kg diet of Thy or ThQ and a blend of both Thy and ThQ at a level of 200 mg/kg diet each. At the end of the feeding trial (12 weeks), the tilapias were challenged intraperitoneally with virulent A. sobria (2.5 × 108 CFU/mL) harboring aerolysin (aero) and hemolysin (hly) genes. The results revealed that tilapias fed diets fortified with a combination of Thy and ThQ displayed significantly enhanced growth rate and feed conversion ratio. Notably, the expression of the genes encoding digestive enzymes (pepsinogen, chymotrypsinogen, α-amylase and lipase) and muscle and intestinal antioxidant enzymes (glutathione peroxidase, catalase and superoxide dismutase) was significantly upregulated in Thy/ThQ-fed fish. An excessive inflammatory response was subsided more prominently in the group administrated Thy/ThQ as supported by the downregulation of il-β, il-6 and il-8 genes and in contrast, the upregulation of the anti-inflammatory il-10 gene. Remarkably, dietary inclusion of Thy/ThQ augmented the expression of autophagy-related genes, whilst it downregulated that of mtor gene improving the autophagy process. Furthermore, Thy/ThQ protective effect against A. sobria was evidenced via downregulating the expression of its aero and hly virulence genes with higher fish survival rates. Overall, the current study encouraged the inclusion of Thy/ThQ in fish diets to boost their growth rates, promote digestive and antioxidant genes expression, improve their immune responses and provide defense against A. sorbia infections with great economic benefits.

The Protective Effect of Mulberry Leaf Flavonoids on High-Carbohydrate-Induced Liver Oxidative Stress, Inflammatory Response and Intestinal Microbiota Disturbance in Monopterus albus

An 8-week feeding trial with high-carbohydrate- and 100, 200 and 300 mg/kg mulberry leaf flavonoids (MLF)-supplemented diets (HCF1, HCF2 and HCF3, respectively) was conducted to evaluate the protective effect of MLF on oxidized high-carbohydrate-induced glucose metabolism disorder, liver oxidative damage and intestinal microbiota disturbance in Monopterus albus. The results showed that HC diets had significant negative effects on growth, glucose metabolism, liver antioxidant and immunity, as well as intestinal microbiota, in comparison to CON diets. However, WGR and SR in the HCF3 group dramatically increased compared to the HC group. With the increase of MLF in the HC diet, the activities of glycolysis and antioxidant enzymes in the liver tended to increase, while the changes of gluconeogenesis-related enzyme activities showed the opposite trend and significantly changed in the HCF3 group. Additionally, MLF supplementation dramatically increased the mRNA expression involved in glycolysis, antioxidative enzymes and anti-inflammatory cytokines in comparison with the HC group. Furthermore, gluconeogenesis and pro-inflammatory cytokine genes’ expression dramatically decreased. Furthermore, the proportion of Clostridium and Rhodobacter in the HC group dramatically declined, and the proportion of Lactococcus dramatically increased, compared to the HC group. In addition, 300 mg/kg MLF supplementation significantly improved the species composition and homeostasis of intestinal microbiota. These results indicate that MLF can alleviate the negative effects of low growth performance, glucose metabolism disorder, liver oxidative damage and intestinal microbiota disturbance caused by HC diets, and the relief of MLF is dose-related.

Developmental toxicity of glyphosate on embryo-larval zebrafish (Danio rerio)

Glyphosate (GLY) induces developmental toxicity in fish, but research on the toxicity mechanism is limited. In this study, zebrafish embryos were exposed for 120 hpf to 0.7, 7, and 35 mg L-1 GLY. The results show that GLY treatment induced developmental toxicity in the fish, including premature hatching, reduced heartbeats, pericardial and yolk sac oedema, swim bladder deficiency, and shortened body length, which was possibly due to a significantly decreased triiodothyronine (T3)/thyroxine (T4) ratio and the abnormal expression patterns of hypothalamic-pituitary-thyroid (HPT) (crh, tshβ, tr α, tr β, and t tr ) and growth hormone/insulin-like growth factor (GH/IGF) axis-related genes (gh, ghrα, ghrβ, igf1, igf1rα, and igf1rβ) in larvae exposed to GLY. In addition, GLY exposure altered the levels of SOD and CAT, increased ROS, promoted malondialdehyde (MDA) content, and significantly altered the levels of endoplasmic reticulum (ER) stress signalling pathway factors (perk, eif2α, gadd34, atf4, ire1α, xbp1, atf6, hspa5, and chop), suggesting that GLY treatment induced oxidative injury and ER stress in the larvae. Further research showed that treatment with a higher concentration of GLY upregulated the levels of iNOS, IL-1β, and TNF-α while inhibiting the expression of IL-10 and TGF-β, suggesting that GLY causes an inflammatory reaction in the larvae. In addition, we also found that apoptosis was induced in the larvae, which was determined by acridine orange staining and abnormal expression of p53, caspase-3, -8, and -9. Taken together, our results demonstrate that GLY exposure altered the T3/T4 ratio, disturbed the expression patterns of HPT and GH/IGF axis-related genes, and induced oxidative and ER stress, inflammatory reactions, and apoptosis in the zebrafish larvae. This investigation contributes to improved understanding of the developmental toxicity mechanism of GLY in fish.

Interactive effects of dietary quercetin nanoparticles on growth, flesh antioxidant capacity and transcription of cytokines and Aeromonas hydrophila quorum sensing orchestrating genes in Nile tilapia (Oreochromis niloticus)

Recently, the concept of incorporating natural products into nanocarriers has been intended to promote fish growth and health via modulating their stability and bioavailability. In this concern, the potential role of reformulated quercetin into nanocarriers was examined, for the first time, on Nile tilapia's performance and immunity, flesh quality and antioxidant indices and disease resistance. Five hundred fish assigned into five experimental groups with formulated diets containing quercetin nanoparticles (QT-NPs) at levels of 0, 100, 200, 300 and 400 mg/kg were challenged with Aeromonas hydrophila (A. hydrophila) after 12 weeks feeding trial. Fish final body weight gain and feed efficiency were significantly maximized in groups enriched with 300 and 400 mg/kg of QT-NPs. Significant reduction in total saturated fatty acids and an elevation in polyunsaturated fatty acids' contents were noticed in fish fed higher QT-NPs doses. The levels of Hydrogen peroxide, reactive oxygen species and malondialdehyde, the markers of meat antioxidant capacity, were reduced by higher inclusion levels of QT-NPs. Accordingly, serum activities and transcriptional levels of GSH-Px, CAT and SOD genes were increased with elevated QT-NPs levels. Immune responses mediated by upregulation of IL-10 and TGF-β and downregulation of IL-1β, IL-8 and TNF-α mRNA levels were found to be positively affected by QT-NPs. Dietary QT-NPs downregulated the expression of ahyI and ahyR quorum sensing genes conferring protection against A. hydrophila challenge. This study concluded that supplementation of quercetin in encapsulated nanoparticles could improve its efficacy making it as a compelling approach to improve fish performance and as a promising drug candidate against A. hydrophila virulence.

Alterations in blood parameters, DNA damage, oxidative stress and antioxidant enzymes and immune-related genes expression in Nile tilapia (Oreochromis niloticus) exposed to glyphosate-based herbicide

In this study, effects of different concentrations (0, 5, 10, 20, 30, and 40 mg/L) of glyphosate-based herbicide (GBH) on Nile tilapia (Oreochromis niloticus) were investigated after a 14-day of exposure. After determination of LC50 value, effects of GBH on hematological and serum biochemical parameters in blood samples, DNA damage, lipid peroxidation and catalase activity in liver tissues, expression levels of antioxidant enzyme-related genes (SOD, CAT, GPx, and GST) and immune-related genes (TGF-β, TGF-α and IL1-β) were evaluated. The LC50 value has been found as 44.4 mg/L for GBH. GBH exposure at all concentrations caused alterations in blood parameters. GBH induced oxidative stress in liver and DNA damage in blood. Antioxidant enzyme-related genes were significantly up-regulated to suppress oxidative stress. On the other hand, the expression levels of immune-related genes decreased in fish exposure to particularly ≥20 mg/L GBH.

Microcystin-Induced Immunotoxicity in Fishes: A Scoping Review

Cyanobacteria (blue-green algae) have been present on Earth for over 2 billion years, and can produce a variety of bioactive molecules, such as cyanotoxins. Microcystins (MCs), the most frequently detected cyanotoxins, pose a threat to the aquatic environment and to human health. The classic toxic mechanism of MCs is the inhibition of the protein phosphatases 1 and 2A (PP1 and PP2A). Immunity is known as one of the most important physiological functions in the neuroendocrine-immune network to prevent infections and maintain internal homoeostasis in fish. The present review aimed to summarize existing papers, elaborate on the MC-induced immunotoxicity in fish, and put forward some suggestions for future research. The immunomodulatory effects of MCs in fish depend on the exposure concentrations, doses, time, and routes of exposure. Previous field and laboratory studies provided strong evidence of the associations between MC-induced immunotoxicity and fish death. In our review, we summarized that the immunotoxicity of MCs is primarily characterized by the inhibition of PP1 and PP2A, oxidative stress, immune cell damage, and inflammation, as well as apoptosis. The advances in fish immunoreaction upon encountering MCs will benefit the monitoring and prediction of fish health, helping to achieve an ecotoxicological goal and to ensure the sustainability of species. Future studies concerning MC-induced immunotoxicity should focus on adaptive immunity, the hormesis phenomenon and the synergistic effects of aquatic microbial pathogens.

The Protective Effect of Taurine on Oxidized Fish-Oil-Induced Liver Oxidative Stress and Intestinal Barrier-Function Impairment in Juvenile Ictalurus punctatus

Dietary lipids provide energy for growth and development and provide fatty acids necessary for normal structure and biological function. However, oxidized lipids cause oxidative stress and intestinal damage. An 8-week feeding trial with fresh fish oil (FFO, control group), oxidized fish oil (OFO), and taurine-supplemented diets (OFOT, OFO + 0.2% of taurine) was conducted to evaluate the protective effect of taurine on oxidized fish-oil-induced liver oxidative stress and intestine impairment in juvenile Ictaluruspunctatus. The results showed that (1) Growth performance was significantly lower in fish fed OFO than in those fed other diets, whereas the opposite occurred in the hepatosomatic index. (2) OFO-feeding significantly increased lipid deposition compared with the FFO group. The addition of taurine ameliorated the OFO-induced increase in lipid vacuolization in the liver, significantly upregulated lpl mRNA expression, and downregulated fas and srebp1 mRNA expression. (3) OFO-feeding significantly reduced oxidative damage of liver. Compared with the OFO group, the OFOT group remarkably upregulated antioxidant enzyme mRNA expression through the Nrf2-Keap1 signaling pathway based on the transcriptional expression. (4) OFO diets induced intestinal physical and immune barrier damage. Compared with the OFO group, OFOT diets remarkably downregulated il-1β, il-6, tnf-α, and il-8 mRNA expression and upregulated tgf-β mRNA expression through the NF-κB signaling pathway. Besides, the addition of taurine to OFO diets significantly upregulated zo-2 and zo-1 mRNA expression, and downregulated claudin-15 and claudin-12 mRNA expression. In conclusion, oxidized-fish-oil diets can cause negative physiological health effects in Ictaluruspunctatus, while adding taurine can increase growth and antioxidant ability, reduce lipid deposition, and improve intestinal health.

Immunotoxic Effects Induced by Microcystins and Cylindrospermopsin: A Review

Cyanotoxin occurrence is gaining importance due to anthropogenic activities, climate change and eutrophication. Among them, Microcystins (MCs) and Cylindrospermopsin (CYN) are the most frequently studied due to their ubiquity and toxicity. Although MCs are primary classified as hepatotoxins and CYN as a cytotoxin, they have been shown to induce deleterious effects in a wide range of organs. However, their effects on the immune system are as yet scarcely investigated. Thus, to know the impact of cyanotoxins on the immune system, due to its importance in organisms’ homeostasis, is considered of interest. A review of the scientific literature dealing with the immunotoxicity of MCs and CYN has been performed, and both in vitro and in vivo studies have been considered. Results have confirmed the scarcity of reports on the topic, particularly for CYN. Decreased cell viability, apoptosis or altered functions of immune cells, and changed levels and mRNA expression of cytokines are among the most common effects reported. Underlying mechanisms, however, are still not yet fully elucidated. Further research is needed in order to have a full picture of cyanotoxin immunotoxicity.

Ammonia stress influences intestinal histomorphology, immune status and microbiota of Chinese striped-neck turtle (Mauremys sinensis)

Ammonia is one of major pollutants in aquatic environment that induces severe stress and toxicity to organisms in aquatic system. The intestine acts a major defense line that protects living organisms from biotic and abiotic stresses. In the current study, we examined the effects of ammonia on intestinal histomorphology, transcriptional levels of intestinal barrier functioning genes and intestinal microbiota of Chinese striped-neck turtle (Mauremys sinensis). Thus, the turtles were placed in water with addition of ammonia at 0 (control), 100, 200 mg L^-1 for 30 days. Our findings showed that ammonia reduced the villus length and induced the inflammatory cells appearance. In addition, the epithelial tight junction genes, claudin and zonola occludin significantly downregulated in ammonia exposed groups as compared to control group (P < 0.05). Similarly, the mRNA expression levels of MUC-2 gene also significantly decreased in ammonia treated groups (P < 0.05). However, the expression levels of intestinal immune related genes such as IL-10, IL-12, TGF-β1, TNF-α and IFN-γ significantly increased (P < 0.05). Furthermore, ammonia changed gut microbial diversity variedly. At the phylum levels, Firmicutes increased, whereas Bacteroidota, Desulfobacterota and Synergistota decreased significantly. Likewise, Lachnospiraceae, Bacteroides, Eubacteriaceae, Desulfovibrio, Muribaculaceae, Bilophila, Cloacibacillus, Christensenellaceae, Ruminococcus and Parabacteroides decreased while, Romboutsia and Turicibacter increased in ammonia exposed groups. In conclusion, ammonia at 100 and 200 mg L^-1 could alter the intestinal barrier function and change the composition of intestinal microbiota, leading to bad health status in M. sinensis.

Negative impacts of microcystin-LR and glyphosate on zebrafish intestine: Linked with gut microbiota and microRNAs?

Microcystin-LR (MC-LR) and glyphosate (GLY) have been classified as a Group 2B and Group 2A carcinogens for humans, respectively, and frequently found in aquatic ecosystems. However, data on the potential hazard of MC-LR and GLY exposure to the fish gut are relatively scarce. In the current study, a subacute toxicity test of zebrafish exposed to MC-LR (35 μg L-1) and GLY (3.5 mg L-1), either alone or in combination was performed for 21 d. The results showed that MC-LR or/and GLY treatment reduced the mRNA levels of tight junction genes (claudin-5, occludin, and zonula occludens-1) and altered the levels of diamine oxidase and D-lactic, indicating increased intestinal permeability in zebrafish. Furthermore, MC-LR and/or GLY treatment remarkably increased the levels of intestinal IL-1β and IL-8 but decreased the levels of IL-10 and TGF-β, indicating that MC-LR and/or GLY exposure induced an inflammatory response in the fish gut. MC-LR and/or GLY exposure also activated superoxide dismutase and catalase, generally upregulated the levels of p53, bax, bcl-2, caspase-3, and caspase-9, downregulated the levels of caspase-8 and caused notable histological injury in the fish gut. Moreover, MC-LR and/or GLY exposure also significantly altered the microbial community in the zebrafish gut and the expression of miRNAs (miR-146a, miR-155, miR-16, miR-21, and miR-223). Chronic exposure to MC-LR and/or GLY can induce intestinal damage in zebrafish, and this study is the first to demonstrate an altered gut microbiome and miRNAs in the zebrafish gut after MC-LR and GLY exposure.

Effects of harmful algal blooms on stress levels and immune functioning in wetland-associated songbirds and reptiles

Harmful algal blooms (HABs), caused primarily by nutrient input from agricultural runoff, are a threat to freshwater systems worldwide, and are further predicted to increase in size, frequency, and intensity due to climate change. HABs occur annually in the Western Basin of Lake Erie (Ohio, USA), and these blooms become toxic when dominated by cyanobacteria that produce the liver toxin microcystin. Although we are making substantial inroads toward understanding how microcystin affects human health, less is known about effects of microcystin on wildlife exposed to HABs. Wetland-associated songbirds (barn swallows, Hirundo rustica, and red-winged blackbirds, Agelaius phoeniceus) and reptiles (Northern watersnakes, Nerodia sipedon, and painted turtles, Chrysemys picta) were sampled from wetlands exposed to chronically high microcystin levels due to a prolonged HAB event, and from unexposed, control wetlands. Physiological stress levels and several measures of immune functioning were compared between the HAB-exposed and control populations. Physiological stress levels, measured as heterophil:lymphocyte ratios, were higher in barn swallows, red-winged blackbirds, and Northern watersnakes exposed to a chronic HAB compared to unexposed, control individuals, but painted turtles did not differ in physiological stress levels between HAB-exposed and control individuals. Neither barn swallows nor red-winged blackbirds differed in immune functioning between populations, but HAB-exposed watersnakes had higher bactericidal capacity than control snakes, and HAB-exposed painted turtles had lower bactericidal capacity than control turtles. These results suggest that even when HABs do not cause direct mortality of exposed wildlife, they can potentially act as a physiological stressor across several taxa, and furthermore may compromise immune functioning in some species.

Characterization of ayu (Plecoglossus altivelis) urocortin: The function of an endocrine factor in monocyte/macrophage regulation

Urocortin (UCN) is a hormone in the hypothalamic-pituitary-adrenal axis that is expressed in various immune cells. However, the function of teleost UCN in the immune system remains unclear. In this study, we cloned the cDNA sequence of UCN from ayu Plecoglossus altivelis (PaUCN). Sequence and phylogenetic tree analyses showed that PaUCN clustered within the fish UCN 1 group and was most related to the rainbow trout (Oncorhynchus mykiss) UCN. PaUCN was expressed in all tested tissues and its expression increased in the liver, spleen, head kidney, and gill upon Vibrio anguillarum infection. Mature PaUCN protein (mPaUCN) treatment affected the phagocytosis and bacterial killing of monocytes/macrophages (MO/MФ). mPaUCN reduced pro-inflammatory cytokine expression in MO/MФ, which was partially mediated via interaction with ayu interleukin-6. mPaUCN reduced bacterial load and increased the survival of V. anguillarum-infected ayu. Overall, UCN as an endocrine factor regulates the immune response of ayu after infection by activating MO/MФ, thus contributing to enhance fish survival.

Cytotoxic and immunological responses of fish leukocytes to nodularin exposure in vitro

Nodularin (NOD) is a cyclic peptide released by bloom-forming toxic cyanobacteria Nodularia spumigena commonly occurring in brackish waters throughout the world. Although its hepatotoxic effects are well known, other negative effects of NOD have not yet been completely elucidated. The present study aims were to evaluate and compare the cytotoxic and immunotoxic effects of the toxin on primary leukocytes (from head kidney [HK]) and stable fish leukocytes (carp leucocyte cell line [CLC] cells). The cells were incubated with the cyanotoxin at concentrations of 0.001, 0.01, 0.05, or 0.1 μg/ml. After 24 h of exposure, the concentrations ≥0.05 μg/ml of toxin resulted in cytotoxicity in the primary cells, while in CLC cells, the toxic effect was obtained only with the highest concentration. Similarly, depending on the concentration, exposure to NOD causes a significant inhibition of chemotaxis of the phagocytic abilities of primary leukocytes and a significant reduction in the proliferation of lymphocytes isolated from the HKs. Moreover, CLC cells and HK leukocytes incubated with this toxin at all the mentioned concentrations showed an increased production of reactive oxygen and nitrogen species. NOD also evidently influenced the expression of genes of cytokine TNF-α and IL-10 and, to a minor extent, IL-1β and TGF-β. Notably, the observed changes in the mRNA levels of cytokines in NOD-exposed cells were evident, but not clearly dose-dependent. Interestingly, NOD did not affect the production and release of IL-1β of the CLC cells. This study provides evidence that NOD may exert cytotoxicity and immune-toxicity effects depending on cell type and toxin concentration.

Effects of chronic nitrate exposure on the intestinal morphology, immune status, barrier function, and microbiota of juvenile turbot (Scophthalmus maximus)

Coming along with high water reuse in sustainable and intensive recirculating aquaculture systems (RASs), the waste products of fish in rearing water is continuously accumulated. Nitrate, the final product of biological nitrification processes, which may cause aquatic toxicity to fish in different degrees when exposed for a long time. Therefore, the present study was conducted to evaluate the impact of chronic nitrate exposure on intestinal morphology, immune status, barrier function, and microbiota of juvenile turbot. For that, groups of juvenile turbot were exposed to 0 (control check, CK), 50 (low nitrate, L), 200 (medium nitrate, M), and 400 (high nitrate, H) mg L^-1 nitrate-N in small-sized recirculating aquaculture systems. After the 60-day experiment period, we found that exposure to a high concentration of nitrate-N caused obvious pathological damages to the intestine; for instance, atrophy of intestinal microvilli and necrosis in the lamina propria. Quantitative real-time PCR analysis revealed a significant downregulation of the barrier forming tight junction genes like occludin, claudin-like etc. under H treatment (P < 0.05). Intestinal MUC-2 expression also decreased significantly in the nitrate treatment groups compared to that in the control (P < 0.05). Additionally, the expression of HSP70 and HSP90 heat-shock proteins, toll-like receptor-3 (TLR-3), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) significantly increased (P < 0.05), whereas that of transforming growth factor-β (TGF-β), lysozyme (LYS), and insulin-like growth factor-I (IGF-I) significantly decreased with H treatment (P < 0.05). The results also revealed that intestinal microbial community was changed following nitrate exposure and could alter the α-diversity and β-diversity. Specifically, the proportion of intrinsic flora decreased, whereas that of the potential pathogens significantly increased with M and H treatments (P < 0.05). In conclusion, chronic nitrate exposure could weaken the barrier function and disturb the composition of intestinal microbiota in marine teleosts, thereby harming their health condition.

Effects of dietary leucine levels on intestinal antioxidant status and immune response for juvenile golden pompano (Trachinotus ovatus) involved in Nrf2 and NF-κB signaling pathway

The aim of the study was to evaluate the effects of dietary leucine level on growth performance, intestinal antioxidant status and immune response involved in Nrf2 and NF-κB signaling pathway in juvenile golden pompano (Trachinotus ovatus). A total of 450 juvenile golden pompano (9.15 ± 0.04 g) were fed three isonitrogenous diets with graded leucine levels [1.25% (control), 2.77% and 5.84%] for 8 weeks. The results showed that, compared with the control group, the WG was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05), and the 5.84% dietary leucine group had a tendency to increase. Compared to control group, 5.84% dietary leucine group significantly decreased the moisture and ash contents of whole body (P < 0.05), meanwhile, 2.77% dietary leucine group significantly decreased moisture content of whole body, but significantly improved the whole body crude lipid content (P < 0.05). Compared with the control group, the ALP level was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). Inversely, the AST and ALT activities were significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). Compared with the control group, GPx, T-AOC, SOD activities in group of 2.77% dietary arginine level were significantly increased (P < 0.05). However, MDA level showed a reverse trend, which was significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). 2.77% dietary leucine levels significantly increased the relative expressions of Nrf2, HO-1, Cu/Zn-SOD, Mn-SOD and CAT (P < 0.05). In contrast, the relative expression of Keap1 showed a converse trend. Compared with the control group, the relative expressions of NF-κB, TNF-α and IL1-β were significantly lowered in fish fed with 2.77% of dietary leucine (P < 0.05). Additionally, 2.77% dietary leucine level significantly improved the relative expressions of TGF-β and IL-10 (P < 0.05). The 2.77% dietary leucine level significantly increased the muscular thickness compared with 5.84% dietary leucine level (P < 0.05). Furthermore, compared with the control group, the villus height and goblet cell counts were significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). These results indicated that the optimum dietary leucine plays an important role in promoting growth, enhancing antioxidant and immunity to maintain the intestinal health status of juvenile golden pompano.

Gut immune functions and health in Atlantic salmon (Salmo salar) from late freshwater stage until one year in seawater and effects of functional ingredients: A case study from a commercial sized research site in the Arctic region

The present study was conducted to strengthen the knowledge on gut immune functions and health in Atlantic salmon under large scale, commercial conditions in the Arctic region of Norway. Two groups of fish were monitored, one fed a series of diets without functional ingredients (Ref) and the other diets with functional ingredients (Test). The nutritional composition of the two diet series varied in parallel according to the nutrient requirements of the fish during the observation time. The content of functional ingredients in the Test diets, i.e. nucleotides, yeast cell walls, a prebiotic and essential fatty acids, varied in accordance with a strategy developed by the feed company. The fish were observed at four sampling time points, the first (FW) in May 2016 two weeks before seawater transfer, the other three throughout the following seawater period until the fish reached a size of about 2 kg, i.e. in June, four weeks after seawater transfer (SW1); in November (SW2), and in April the following year (SW3). Gut health was assessed based on histopathological indicators of lipid malabsorption and gut inflammation, expression of gut immune, barrier and other health related genes, plasma biomarkers, somatic indices of intestinal sections, as well as biomarkers of digestive functions. Seawater transfer of the fish (SW1 compared to FW) caused a marked lowering of expression of genes related to immune and barrier functions in the distal intestine, i.e. cytokines (il1β, il10, tgfβ, ifnγ), T-cell markers (cd3γδ), myd88 and tight junction proteins (zo-1, claudin-15, claudin-25b), indicating suppressed immune and barrier functions. At SW2 and SW3, most of the immune biomarkers showed values similar to those observed at FW. The development of plasma cholesterol and triglyceride levels showed similar picture, with markedly lower levels after seawater transfer. Lipid malabsorption was observed in particular in fish from SW1 and SW2, as indicated by hyper-vacuolation of the pyloric caeca enterocytes with concurrently increased expression levels of plin2. Regarding effects of functional ingredients, significantly lower condition factor and plasma triglyceride level were observed for Test-fed fish at SW2, indicating a metabolic cost of use of a mixture of nucleotides, yeast cell walls and essential fatty acids. No clear effects of functional ingredients on expression of gut immune genes and other health indexes were observed through the observation period. The great, temporary lowering of expression of gut immune and barrier genes at SW1 is suggested to be an important factor underlying the increased vulnerability of the fish at this time point. Our findings regarding supplementation with functional ingredients raise questions whether some of these ingredients overall are beneficial or might come with a metabolic cost. Our results highlight the need for a better understanding of the cause and consequences of the suppression of gut immune functions of farmed Atlantic salmon just after seawater transfer, and the use of functional ingredients under commercial conditions.

Quercetin affects shoaling and anxiety behaviors in zebrafish: Involvement of neuroinflammation and neuron apoptosis

Quercetin, a potential fish food supplement, has been reported to process many beneficial properties. However, some negative effects of quercetin have been observed, which pointed out necessity for additional studies to evaluate its safety. Therefore, the present study investigated effects of quercetin (0.01, 0.1, 1, 10, 100 and 1000 μg/L) on shoaling and anxiety behaviors through novel tank tests in zebrafish (Danio rerio). Furthermore, oxidative stress, neuroinflammation and apoptosis in the brains were examined to learn more about mechanisms of action related to quercetin. The results showed that quercetin at the lower concentrations exerted beneficial effects on shoaling and anxiety behaviors. On the contrary, when quercetin was up to 1000 μg/L, it exerted detrimental effects shown as decreases of movement and increases of anxiety behaviors. Generally, U-shaped responses of antioxidant enzyme activities (superoxide dismutase and catalase), and inversed U-shaped responses of inflammatory mediators (cyclooxygenase-2) and cytokines (interleukin-1β, interleukin-6, interleukin-10, and tumor necrosis factor α) to quercetin treatment were found in the brains. In addition, quercetin at the lower concentrations attenuated cell apoptosis, while even more apoptosis was found at the 1000 μg/L quercetin group. In conclusion, quercetin could exert beneficial or detrimental effects on the shoaling and anxiety behaviors depending on the treatment concentrations, and the underlying mechanisms are potentially associated with neuroinflammation and neuron apoptosis.

Effects of Dietary Andrographolide Levels on Growth Performance, Antioxidant Capacity, Intestinal Immune Function and Microbioma of Rice Field Eel (Monopterus Albus)

An eight-week feeding trial was conducted to investigate the effects of dietary andrographolide on the growth performance, antioxidant capacity in the liver, intestinal inflammatory response and microbiota of Monopterus albus. A total of 900 health fish (25.00 ± 0.15 g) were randomly divided into five groups: AD1 (the basal diet) as the control, and AD2, AD3, AD4 and AD5 groups, which were fed the basal diet supplemented with 75, 150, 225 and 300 mg/kg andrographolide, respectively. The results showed that compared with the control group, dietary andrographolide supplementation (1) significantly increased trypsin and lipase activities in the intestine, and increased the weight gain rate but not significantly; (2) significantly increased the levels of glutathione reductase (GR), glutathione (GSH) and glutathione peroxidase (GPx) and the content of in the liver; significantly decreased the contents of reactive oxygen species (ROS) and malondialdehyde (MDA); remarkably upregulated the Nrf2, SOD1, GSTK and GSTO mRNA levels in the liver; downregulated the Keap1 mRNA level; (3) significantly increased the villi length and goblet cell numbers in the intestine, remarkably upregulated the Occludin mRNA level in the intestine, downregulated the Claudin-15 mRNA level; (4) remarkably upregulated the IL-10, TGF-β1 and TGF-β3 mRNA levels in the intestine; downregulated the IL-12β and TLR-3 mRNA levels; (5) significantly decreased the richness and diversity of the intestinal microbioma, increased the percentages of Fusobacteria and Firmicutes and significantly decreased the percentages of Cyanobacteria and Proteobacteria. In conclusion, these results showed that dietary low-dose andrographolide (75 and 150 mg/kg) promoted growth and antioxidant capacity, regulated the intestinal microbioma, enhanced intestinal physical and immune barrier function in rice field eel.

Effects of extreme ambient temperature in European seabass, Dicentrarchus labrax acclimated at different salinities: Growth performance, metabolic and molecular stress responses

Extreme weather events are becoming more intense and frequent as a result of climate change. The modulation of hemato-physiological potential as a compensatory response to extreme warm events combined with different salinities is poorly understood. This study aimed to assess the hemato-physiological and molecular response of European seabass, Dicentrarchus labrax exposed to extreme warm temperature (33 °C) after prior acclimatization at 32 psu, 12 psu, 6 psu, and 2 psu water. Fish were acclimated to 32 psu, 12 psu, 6 psu, and 2 psu followed by 10 days extreme warm (33 °C) exposure. Along with growth performance and survival, hemato-physiological response and molecular response of fish were recorded. Fish held at 32 psu and 2 psu exhibited significantly lower growth performance and survival than those at 12 psu and 6 psu (p < 0.05). Red blood cells (RBC), hematocrit, and hemoglobin content were significantly decreased, while white blood cells (WBC), erythrocytic cellular abnormalities (ECA) and erythrocytic nuclear abnormalities (ENA) were found to increase significantly in 32 psu and 2 psu fish (p < 0.05). Plasma lactate was found to increase significantly in 32 psu fish on day 10 (p < 0.05). Activities of glutathione peroxidase (GPx), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and TNF-α expression increased significantly in 32 psu and 2 psu fish (p < 0.05). Most of the repeated measured parameters indicated limited acclimation capacity during the extreme warm exposure at all four salinity groups. However, overall results indicate that European seabass acclimatized at 12 psu and 6 psu salinities, can cope better during extreme warm exposure (33 °C).

Effects of dietary fish meal replacement by fermented moringa (Moringa oleifera Lam.) leaves on growth performance, nonspecific immunity and disease resistance against Aeromonas hydrophila in juvenile gibel carp (Carassius auratus gibelio var. CAS III)

This study was aimed to evaluate the effects of partial replacement of fish meal by fermented moringa leaves (FMLs) on growth performance, serum biochemistry, antioxidant status, nonspecific immunity, and resistance against Aeromonas hydrophila in juvenile gibel carp (Carassius auratus gibelio var. CAS III). Four isonitrogenous and isoenergetic balanced diets, including three FML diets (substituting 20%, 40%, 60% of the fish meal in basal diet, F20, F40 and F60, respectively) and a basal diet (a diet containing 10% fish meal) were used. Each diet was randomly allocated to four fish groups (F20, F40, F60 and control) reared in a recirculating system. After 50 days of the feeding trial, fish were challenged by A. hydrophila. The result revealed that final mean body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), feed efficiency (FE) and survival rate (SR) were significantly increased (P < 0.05) in F20 and F40 groups compared with the control group. Decreased hepatosomatic index (HSI), body crude lipid, serum aspartate transaminase (AST) and serum alanine aminotransferase (ALT) activities, and increased serum alkaline phosphatase (AKP) and serum glutathione peroxidase (GPx) activities were observed in F40 and F60 groups compared with the control and F20 groups. All FMLs-supplemented groups increased (P < 0.05) serum superoxide dismutase (SOD), catalase (CAT) and lysozyme activities, complement component 3 (C3) and serum immunoglobulin M (IgM) concentration, or decreased serum malondialdehyde (MDA) and protein carbonyl (PCC) contents (P < 0.05). After the challenge test, the significant downregulation of toll-like receptors2 (TLR2), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-8 mRNA transcription levels was observed in spleens of FMLs supplemented groups. Dietary F40 and F60 showed higher (P < 0.05) relative percent survival (RPS) (48.72% and 43.59%, respectively) against A. hydrophila infection than control. These results indicate that, as a dietary fish meal substitute, FMLs enhance the growth, and antioxidant and immune response, and regulate the expression of immune-related genes and increase disease resistance against A. hydrophila via TLR2 pathway in gibel carp, with greatest effects of 40% fish meal substitution.

The effects of the neurotoxic agent emamectin benzoate on the expression of immune and stress-related genes and blood serum profiles in the Rainbow trout

Emamectin, a neurotoxic agent, is a semi-synthetic insecticide that belongs to the Avermectin family and is used against helmintic infections in the Salmonidae family. Its secondary effects are not clear; thus, the aim of this study was to investigate the only effects of emamectin benzoate on various biochemical parameters (AST, ALT, GGT, total protein, albumin and glucose) in serum and expressional changes of IL-1β, TNF-α, HSP70 and IL-8 in liver and spleen. For the purpose stated above, rainbow trout (n = 15) were administered 50 μg EB per kg fish daily for 7, 14 and 21 days. The results indicated that weight gains did not change (p  >  0.05), AST increased at day 21 (p < 0.05), while the changes of other biochemical parameters were not significant (p > 0.05). The changes in expression of IL-1β, TNF-α and HSP70 were significant (p < 0.05), while the changes of IL-8 expressions were not significant (p ˃ 0.05). In a conclusion, EB changed immun and stress-related gene expression in liver and spleen, and furthermore, AST changed in a dose- and time-dependent manner. The results imply that emamectin benzoate cause stress. This study is helpful to understand the effects of avermectin pharmaceutical family.

Dietary selenium enhances the growth and anti-oxidant capacity of juvenile blunt snout bream (Megalobrama amblycephala)

Sodium selenite was added to basal diet at five levels (0.10, 0.42, 0.67, 1.06 and 1.46 mg Se/kg) and fed fish for 8 weeks. The dietary selenium requirement of juvenile blunt snout bream (Megalobrama amblycephala) was quantified. Dietaryseleniums at 0.67-1.06 mg Se/kg improved weight gain rate, specific growth rate and feed efficiency. The optimal amount was 0.96 mg/kg, for which the specific growth rate was 1.798%/day and the weight gain rate was 173.852% (p < 0.05). Se deposition in muscle was increased (p < 0.05) at ≥0.67 mg/kg, but moisture, protein, lipid and ash content were not affected. Physiological status and lipid metabolism were improved by 1.06-1.46 mg/kg dietary selenium based on total protein and albumin in plasma, and total cholesterol and triglycerides (p < 0.05). Activities of hepatic anti-oxidant enzymes catalase, total superoxide dismutase, glutathione peroxidase and reduced glutathione were enhanced at Se1.06 (p < 0.05). However, malondialdehyde content was lowered at Se1.06 (p < 0.05). Expression of anti-inflammatory cytokines, nuclear factor erythroid 2-related factor 2 (Nrf2) and kelch-like ECH-associated protein 1 (Keap-1) in liver were elevated at Se1.06 (p < 0.05), as were mRNA levels of glutathione peroxidase, copper zinc superoxide dismutase and catalase. Expression of pro-inflammatory cytokines, interleukin 8, tumour necrosis factor-α and transforming growth factor-β were inhibited at 0.67-1.46 mg/kg (p < 0.05). In general, 0.96 mg/kg was optimal, and optimal selenium enhanced antioxidant stress tolerance and anti-inflammatory ability.

The effects of quercetin on immunity, antioxidant indices, and disease resistance in zebrafish (Danio rerio)

The main purpose of this study was to evaluate the immunity, antioxidant indices, and disease resistance of quercetin in zebrafish (Danio rerio). A total of 630 fish were assigned to 21 tanks with 30 fish/tank, and they were exposed to 0, 0.01, 0.1, 1, 10, 100, and 1000 μg/L quercetin, respectively, for 56 days. Results indicated that the immune indices including acid phosphatase (ACP), myeloperoxidase (MPO), lysozyme activities, and Complement 3 (C3), C4, IgM contents were significantly higher in 1 μg/L quercetin group than these parameters in the control group (P < 0.05). TNF-α and IL-8 mRNA expressions significantly decreased as the levels of quercetin increased up to 1 μg/L and increased thereafter (P < 0.05). 1 and 10 μg/L quercetin groups showed significantly lower TNF-α and IL-8 mRNA levels than the quercetin-free group. Transforming growth factor-β and IL-10 mRNA levels showed an obviously opposite trend with TNF-α expression. The SOD, GPX, CAT, T-AOC activities, and SOD and GPX gene expression in the liver were enhanced with increasing quercetin up to 1 μg/L, and decreased thereafter. MDA contents were affected by quercetin, in which 1 and 10 μg/L quercetin had a significantly lower level than that of the control group (P < 0.05). Defensin and Leap-II mRNA expression in the liver were the highest for fish exposed to 1 μg/L quercetin. The fish that exposed to 1 μg/L quercetin also showed a significantly higher survival rate than these of fish exposed to 0, 0.01, and 1000 μg/L quercetin (P < 0.05). In conclusion, the optimal level of quercetin promotes immunostimulant properties, antioxidant indices, and disease resistance of zebrafish.

Microcystin-LR-induced changes of hepatopancreatic transcriptome, intestinal microbiota, and histopathology of freshwater crayfish (Procambarus clarkii)

As a hepatotoxin, microcystin-LR (MC-LR) poses a great threat to aquatic organisms. In this research, the hepatopancreatic transcriptome, intestinal microbiota, and histopathology of Procambarus clarkii (P. clarkii) in response to acute MC-LR exposure were studied. RNA-seq analysis of hepatopancreas identified 372 and 781 differentially expressed genes (DEGs) after treatment with 10 and 40 μg/L MC-LR, respectively. Among the DEGs, 23 genes were immune-related and 21 genes were redox-related. GO functional enrichment analysis revealed that MC-LR could impact nuclear-transcribed mRNA catabolic process, cobalamin- and heme-related processes, and sirohydrochlorin cobaltochelatase activity of P. clarkii. In addition, the only significantly enriched KEGG pathway induced by MC-LR was galactose metabolism pathway. Meanwhile, sequencing of the bacterial 16S rRNA gene demonstrated that MC-LR decreased bacterial richness and diversity, and altered the intestinal microbiota composition. At the phylum level, after 96 h, the abundance of Verrucomicrobia decreased after treatment with 10 and 40 μg/L MC-LR, while Firmicutes increased in the 40 μg/L MC-LR-treated group. At the genus level, the abundances of 15 genera were significantly altered after exposure to MC-LR. Our research demonstrated that MC-LR exposure caused histological alterations such as structural damage of hepatopancreas and intestines. This research provides an insight into the mechanisms associated with MC-LR toxicity in aquatic crustaceans.

Parental Transfer of Microcystin-LR-Induced Innate Immune Dysfunction of Zebrafish: A Cross-Generational Study

Transgenerational effects of microcystin-LR (MC-LR) released by cyanobacterial blooms have become a hot topic. In the present study, adult zebrafish pairs were exposed to 0, 0.4, 2, and 10 μg/L MC-LR for 60 days and the embryos (F1 generation) were hatched without or with continued MC-LR exposures at the same concentrations until 5 days postfertilization (dpf). The results showed the existence of MC-LR both in F0 gonads and in F1 embryos and indicated that MC-LR could be transferred directly from the F0 adult fish to F1 offspring. The adverse effects on sex hormone levels, sexual development, and fecundity in F0 generation along with abnormal development in F1 offspring were observed. Furthermore, downregulation of antioxidant genes (cat, mn-sod, gpx1a) and upregulation of innate immune-related genes (tlr4a, myd88, tnfα, il1β) as well as increased proinflammation cytokine contents (TNF-α, IL-1β, IL-6) were noticed in F1 offspring without/with continued MC-LR exposures. In addition, significant differences between the two F1 embryo treatments demonstrated that continuous MC-LR exposure could result in a higher degree of inflammatory response compared to those without MC-LR exposure. Our findings revealed that MC-LR could exert cross-generational effects of immunotoxicity by inhibiting the antioxidant system and activating an inflammatory response.

Effects of long-term crowding stress on neuro-endocrine-immune network of rainbow trout (Oncorhynchus mykiss)

Low levels of stresses cause eustress while high stressful situations result in distress. Female rainbow trout (Oncorhynchus mykiss) was reared under crowded conditions to mimic the stressful environment of intensive fishery production. Trout was stocked for 300 days with initial densities of 4.6 ± 0.02 (final: 31.1 ± 0.62), 6.6 ± 0.03 (final: 40.6 ± 0.77), and 8.6 ± 0.04 (final: 49.3 ± 1.09) kg/m³ as SD1, SD2 and SD3. We assessed molecular, cellular and organismal parameters to understand the flexibility of neuro-endocrine-immune network during stress. Trout with higher initial density (SD3) displayed the slightly activated hypothalamus-pituitary-interrenal (HPI) axis with positively increased antioxidant enzyme activities and anti-inflammatory cytokine transcriptions on day 60 or 120. These results indicated that low level of stress was capable of exerting eustress by activating neuro-endocrine-immune network with beneficial adaptation. Transition from eustress to distress was induced by the increased intensity and duration of crowding stress on day 240 and 300. The prolonged activation of HPI axis resulted in suppressed growth hormone-insulin-like growth factor (GH-IGF) axis, up-regulated cytokine transcriptions and severe reactive oxygen species stress. Stress means reset of neuro-endocrine-immune network with energy expenditure and redistribution. Digestive ability of trout with distress was also inhibited on day 240 and 300, indicating a decreased total energy supplement and energy distribution for functions are not necessary for surviving such as growth and reproduction. Consequently, we observed the dyshomeostasis of energy balance and neuro-endocrine-immune network of trout during long-term crowding conditions.

Effects of dietary fenugreek seed extracts on growth performance, plasma biochemical parameters, lipid metabolism, Nrf2 antioxidant capacity and immune response of juvenile blunt snout bream (Megalobrama amblycephala)

Dietary administration of some plant-derived substances have been proved of great economic value in aquaculture. In order to investigate the effects of dietary fenugreek seed extracts (FSE) on juvenile blunt snout bream (Megalobrama amblycephala), a feeding trial was conducted for 8 weeks. The results showed that final weight (FW), weight gain (WG), feed conversion ratio (FCR) and specific growth rate (SGR) were not significantly affected by dietary FSE levels. The whole body lipid contents of fish fed with 0.04%, 0.08% and 0.16% FSE diets were significantly lowered compared to the control group. Dietary FSE diets significantly affected plasma complement component 3 (C3), immunoglobulin M (IgM), albumin (ALB) and total protein (TP). The relative expressions of acetyl CoA carboxylase (ACC), fatty acid synthase (FAS) and sterol regulatory element binding protein-1 (SREBP1) mRNA in the liver of fish decreased significantly with increasing dietary FSE levels from 0% up to 0.04%. FSE supplementation diets lowered the liver pro-inflammatory genes expressions by regulating tumor necrosis factor-α (TNF-α) and interleukin 8 (IL-8) mRNA levels and increased anti-inflammatory genes expression by regulating transforming growth factor (TGF-β) and interleukin 10 (IL-10). FSE diets increased growth factor-1 (IGF-1) and target of rapamycin (TOR) mRNA levels from 0% up to 0.04%, 0.04% FSE diets significantly increased growth factor-1 (IGF-1) mRNA levels and S6 kinase-polypeptide 1 (S6K1) mRNA levels compared to the control group. 0.04% FSE diets significantly increased superoxide dismutase (SOD) activities and 0.08% FSE diets significantly increased catalase (CAT) and glutathione peroxidase (GPx) activities, 0.16% FSE diets significantly increased total antioxidant capacity (T-AOC) activities compared to the control group. Additionally, compared to the control group, 0.04% dietary FSE significantly up-regulated nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA levels and glutathione peroxidase-1 (GPx1) mRNA levels, at the same time, 0.02%, 0.04%, 0.08%, 0.16% FSE diets significantly down-regulated kelch-like ECH-associated protein 1 (Keap1) mRNA levels. However, no significant effects were observed on copper zinc superoxide dismutase (Cu/Zn-SOD) and manganese superoxide dismutase (Mn-SOD). Our study indicated that dietary FSE could improve plasma biochemical parameters, regulate lipid metabolism related genes, promote Nrf2 antioxidant capacity and enhance immune response of juvenile blunt snout bream.

Biochemical and molecular impacts of glyphosate-based herbicide on the gills of common carp

Glyphosate (GLY)-based herbicide, one of the most widely used herbicides, might cause a series of environmental problems and pose a toxicological risk to aquatic organisms. However, data on the potential hazard and toxicity mechanism of GLY to fish gills are relatively scarce. In this study, a subacute toxicity test of common carp (Cyprinus carpio L.) treated with commercial GLY at 52.08 and 104.15 mg L-1 for 7 d was conducted. The results revealed that GLY exposure significantly inhibited Na+/K+-ATPase and increased AST and ALT activities in the fish gills. The biochemical assays results revealed that GLY treatment remarkably altered the transcriptional levels of HSP70 and HSP90; inhibited the activities of SOD, CAT, GPx, GR, and T-AOC; reduced the contents of GSH, but remarkably promoted MDA and PC contents, suggesting that GLY exposure induced oxidative stress and lipids and proteins damage in the carp gills. Further research revealed that GLY exposure also promoted expression of NF-κB, iNOS, IL-1β, IL-6, IL-8, and TNF-α; altered the levels of IL-10 and TGF-β, indicating that GLY exposure induced inflammatory response in the fish gills. Additionally, we found that GLY exposure activated apaf-1 and bax and inhibited bcl-2, induced caspase-9 and caspase-3 expression and caused remarkable histological damage in the fish gills. These results may further enriches the toxicity mechanistic theory of GLY to fish gills, which may be useful for the risk assessment of GLY and aquatic organism protection.

Chronic exposure to the ionic liquid [C8mim]Br induces inflammation in silver carp spleen: Involvement of oxidative stress-mediated p38MAPK/NF-κB signalling and microRNAs

The present study aimed to determine the chronic toxicity of 1-methyl-3-octylimidazolium bromide ([C₈mim]Br) on the silver carp to further reveal the toxicological mechanisms of ionic liquids. Chronic exposure of silver carp to [C₈mim]Br at concentrations of 1.095 and 4.380 mg/L for 60 d was conducted under laboratory conditions. The results revealed that chronic exposure to [C₈mim]Br inhibited the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) and reduced glutathione (GSH) levels while markedly increasing malondialdehyde (MDA) and protein carbonyl (PC) levels in fish spleen, indicating that [C₈mim]Br treatment induced oxidative stress. Additionally, long-term exposure to [C₈mim]Br markedly upregulated the expressions of nuclear factor-κB (NF-κB), inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), IL-6, tumour necrosis factor-α (TNF-α), and interferon-γ (IFN-γ); altered the levels of transforming growth factor-β (TGF-β); and increased the mRNA levels of p38MAPK, c-fos, c-jun, and c-myc, suggesting that long-term exposure to [C₈mim]Br might promote the inflammatory response in fish spleen and that p38MAPK/NF-κB signalling may potentially be involved in this process. Moreover, [C₈mim]Br-exposure altered lysozyme activity and complement 3 (C3) and immunoglobulin M (IgM) content, indicating that chronic [C₈mim]Br exposure also has immunotoxic effects on silver carp. Furthermore, we also found that [C₈mim]Br exposure reduced miR-125b levels, altered miR-143 levels, and upregulated miR-155 and miR-21 levels, suggesting that these miRNAs may be involved in the [C₈mim]Br-induced inflammatory response in fish spleen. In summary, the present study indicates that chronic exposure to [C₈mim]Br induces inflammation in fish spleen and that oxidative stress-mediated p38MAPK/NF-κB signalling and miRNAs may play a key role in this process.

Microcystin-LR affects the hypothalamic-pituitary-inter-renal (HPI) axis in early life stages (embryos and larvae) of zebrafish

Frequencies and durations of blooms of cyanobacteria are increasing. Some cyanobacteria can produce cyanotoxins including microcystins (MCs). MCs are the most common toxic products of hazardous algal blooms (HABs), with the greatest potential for exposure and to cause toxicity. Recently, MCs have been shown to disrupt endocrine functions. In this study, for the first time, effects of MC-LR on the hypothalamic-pituitary-inter-renal (HPI) axis during early embryonic development (embryos/larvae) of zebrafish (Danio rerio), were investigated. Embryos/larvae of zebrafish were exposed to 1, 10, 100, or 300 μg MC-LR/L during the period of 4-168 h post-fertilization (hpf). Exposure to 300 μg MC-LR/L resulted in significantly greater concentrations of whole-body cortisol than those in controls. Expressions of genes along the HPI axis and mineralocorticoid receptor (MR-) and glucocorticoid receptor (GR-) centered gene networks were evaluated by use of quantitative real-time PCR. Expression of mRNA for crh was significantly down-regulated by exposure to 300 μg MC-LR/L, while expressions of crhbp, crhr1, and crhr2 were significantly up-regulated, relative to controls. MC-LR caused significantly lesser levels of mRNA for steroidogenic genes including hmgra, star, and cyp17, but expression of mRNA for hsd20b was significantly greater than that of controls. Treatment with MC-LR also altered profiles of transcription of MR- and GR-centered gene networks, which might result in multiple responses. Taken together, these results demonstrated that MC-LR affected the corticosteroid-endocrine system of larvae of zebrafish. This study provided valuable insights into molecular mechanisms behind potential toxicity and endocrine disruption of MCs.

Effects of dietary arginine on antioxidant status and immunity involved in AMPK-NO signaling pathway in juvenile blunt snout bream

The present study assessed the effects of dietary arginine on antioxidant status and immunity involved in AMPK-NO signaling pathway in juvenile blunt snout bream. Fish were fed six practical diets with graded arginine levels ranging from 0.87% to 2.70% for 8 weeks. The results showed that compared with the control group (0.87% dietary arginine level), significantly higher mRNA levels of adenosine monophosphate activated protein kinase (AMPK) and nitric oxide synthetase (NOS), activities of total nitric oxide synthetase (T-NOS) and nitric oxide synthetase (iNOS), and plasma nitric oxide (NO) contents were observed in fish fed with 1.62%-2.70% dietary arginine levels. Significantly higher levels of NOS and iNOS were observed in fish fed with 1.62%-2.70% dietary arginine levels in enzyme-linked immune sorbent assay. At dietary arginine levels of 1.22%-2.70%, the mRNA levels of iNOS were significantly improved. Dietary arginine also significantly influenced plasma interleukin 8 (IL-8) and tumour necrosis factor-α (TNF-α) contents. Furthermore, dietary arginine significantly affected the activity and mRNA level of glutathione peroxidase (GPx), the mRNA levels of pro-inflammatory factor including IL-8 and TNF-α and plasma malondialdehyde (MDA) content. However, total superoxide dismutase (T-SOD) activity, plasma complement component 3 (C3) content, plasma immunoglobulin M (IgM) content, plasma interleukin 1β (IL-1β) content and the mRNA levels of copperzinc superoxide dismutase (Cu/Zn-SOD), manganese superoxide dismutase (Mn-SOD) and IL-1β were not significantly affected by dietary arginine. After Aeromonas hydrophila challenge, the death rate was significantly lowered in fish fed with 1.62%-1.96% dietary arginine levels. Furthermore, the mRNA levels of AMPK, NOS and iNOS, plasma NO content and the activities of T-NOS and iNOS showed an upward trend with increasing dietary arginine levels. Significantly higher levels of NOS and iNOS were observed in fish fed with 1.62%-2.70% dietary arginine levels in enzyme-linked immune sorbent assay. At dietary arginine levels of 1.96%-2.31%, T-SOD activities were significantly improved. Significantly higher GPx activities were observed in fish fed with 1.22%-2.70% dietary arginine levels. At dietary arginine levels of 1.22%-2.31%, the plasma TNF-α and IL-8 contents were significantly decreased. Significantly lower plasma IL-1β contents were observed in fish fed 1.62%-1.96% dietary arginine levels. Dietary arginine significantly influenced the mRNA levels of antioxidant and pro-inflammatory genes including Cu/Zn-SOD, Mn-SOD, GPx, IL-8, TNF-α and IL-1β. Significantly higher plasma C3 contents and significantly lower plasma MDA contents were observed in fish fed with 1.62%-1.96% arginine levels. Furthermore, plasma IgM contents were significantly improved at dietary arginine levels of 1.62%-2.31%. However, high dietary arginine group (2.70%) significantly improved the mRNA levels of pro-inflammatory genes including IL-8, TNF-α and IL-1β and plasma MDA, IL-8, TNF-α and IL-1β contents as compared with optimal dietary arginine levels (1.62% and 1.96%). The present results indicate that optimal arginine level (1.62% and 1.96%) could improve antioxidant capacity, immune response and weaken tissues inflammatory involved in arginine-AMPK-NO signaling pathway, while high arginine level resulted in excessive NO production, leading to increase oxidative stress damage and inflammatory response in juvenile blunt snout bream.