Dietary effects of succinic acid on the growth, digestive enzymes, immune response and resistance to ammonia stress of Litopenaeus vannamei

Interaction Between Liver Metabolism and Gut Short-Chain Fatty Acids via Liver-Gut Axis Affects Body Weight in Lambs

The gut-liver axis and its interactions are essential for host physiology. Thus, we examined the jejunal microbiota, fermentation parameters, digestive enzymes, morphology, and liver metabolic profiles in different growth development lambs to investigate the liver-gut axis's role in their development. One hundred male Hu lambs of similar birth weight and age were raised under the same conditions until they reached 180 days of age. Subsequently, the eight lambs with the highest (HADG) and lowest (LADG) average daily weight gains were slaughtered for index assessment. The study indicates that the body weight, carcass weight, propanoic acid, butyric acid, propanoic acid ratio, butyric acid ratio, and digestive enzymes (beta-glucosidase, microcrystalline cellulase, xylanase, and carboxymethyl cellulase) were significantly higher in HDAG lambs than in LADG lambs (p < 0.05). Additionally, there were no significant differences in the jejunal microbiota's structure and function among lambs at different growth development stages (p > 0.05). Overall, our analysis revealed that HADG lambs compared to LADG lambs exhibited an up-regulation of metabolites (such as spermine, cholic acid, succinic acid, betaine, etc.) that were positively correlated with the butyric acid ratio, propanoic acid ratio, propanoic acid, xylanase, microcrystalline cellulase, beta-glucosidase, amylase, carboxymethyl cellulase, carcass weight, and body weight, while these metabolites were negatively correlated with the kidney, acetic acid, acetic acid/ propanoic acid, and acetic acid ratio. Furthermore, there was a significant correlation between liver metabolism and jejunal microbiota. This study revealed significant differences in hepatic metabolites and jejunal fermentation among lambs at different growth stages, which may inform targeted regulation strategies to enhance lamb productivity.

Effects of ammonia exposure and post-exposure recovery in pacific white shrimp, Litopenaeus vannamei: Histological, physiological and molecular responses

The toxic effects of ammonia exposure on Litopenaeus vannamei have been widely reported, including tissue damage, oxidative stress, and metabolic disorders, but the ability of L. vannamei to recover from ammonia damage is still unclear. To further understand the adaptation mechanism of L. vannamei to ammonia, this study explored the effects of ammonia exposure and recovery on histopathology, physiological indicators, and transcriptomic responses. In the ammonia exposure (NH4+-N 25 mg/L) and recovery experiment, shrimp were sampled at 0 h, 24 h, 48 h of exposure, and 24 h, 48 h of recovery. The results showed that histopathological damage to the hepatopancreas and gills caused by short-term ammonia exposure could be alleviated after recovery. Ammonia exposure inhibited superoxide dismutase (SOD) and catalase (CAT) activities, decreased total antioxidant capacity (T-AOC), and increased malondialdehyde (MDA) in shrimp. Restoration of the antioxidant system after exposure mitigated oxidative damage and reduced MDA levels. The inhibition of acid phosphatase (ACP) and alkaline phosphatase (AKP) activities in shrimp caused by ammonia exposure was reversible. Ammonia excretion and metabolism attenuate ammonia toxicity and promote recovery in L. vannamei. Transcriptome analysis identified 1690, 1568, and 1463 differentially expressed genes (DEGs) in the hepatopancreas at 48 h of stress, 24 h, and 48 h of recovery, respectively. KEGG enrichment analysis revealed that ammonia exposure induced oxidative damage, resulting in apoptosis. Furthermore, activation of antioxidant-related pathways, such as glutathione metabolism and peroxisomes, helped reduce oxidative damage during the post-exposure recovery period. The addition of exogenous spermine and spermidine may contribute to post-exposure recovery and enhance ammonia acclimation in L. vannamei. Differential expression of the inflammatory gene STEAP4 in the ammonia stress and recovery phases, as screened by transcriptome analysis, may play a positive role in post-stress recovery. This study demonstrated the reversibility of the toxic effects of ammonia exposure on L. vannamei, complemented the knowledge of the mechanisms of adaptation of shrimp under ammonia exposure, and provided a basis for subsequent ammonia tolerance studies in crustaceans.

Effects of dietary succinic acid supplementation on growth performance, digestive ability, intestinal development and immunity of large yellow croaker (Larimichthys crocea) larvae

The application of artificial micro-diet is an effective way to improve and standardize the quality of aquatic animal larvae. However, the widespread adoption of micro-diet faces a bottleneck due to the limited utilization capacity of the larvae. A 30-day feeding experiment was carried out to investigate the effect of dietary succinic acid (SA) on the growth performance, digestive ability, intestinal development, and immunity of large yellow croaker larvae (initial body weight 11.33 ± 0.57 mg). Four isonitrogenous and isolipidic diets were formulated, incorporating 0.00 %, 0.01 %, 0.02 % and 0.03 % SA separately. The results showed that a diet with 0.02 % SA significantly increased both the final body weight and the specific growth rate of the larvae. Regarding digestive ability, 0.01 % SA supplementation significantly enhanced trypsin activity in both intestinal and pancreatic segments. In addition, 0.01 % SA supplementation notably improved amylase activity in the intestinal segment, while diets with 0.01%-0.02 % SA significantly improved lipase activity in the pancreatic segment. In terms of intestinal development, 0.01 % SA supplementation remarkably boosted the activities of alkaline-phosphatase and leucine-aminopeptidase on brush border membrane in intestine. Furthermore, 0.03 % SA supplementation significantly increased the expression of occludin. In terms of immunity, larvae fed diets with 0.01%-0.02 % SA exhibited significantly higher lysozyme activity compared to the control group. Supplementation with 0.01 % SA also significantly increased both iNOS activity and NO content. In summary, the findings of this study suggested that supplementing 0.02 % SA can improve the growth performance of large yellow croaker larvae by improving digestive enzymes activities, promoting intestinal development, and enhancing nonspecific immunity.

An Overview of the Biological Functions and Mechanisms of Action of Medicinal Plants and Seaweeds in the Shrimp Culture

Diseases are major constraints to developing large-scale aquaculture practices in many countries. For decades, synthetic chemotherapeutic agents have been widely applied both as prophylactics and therapeutics to inhibit and control aquatic disease outbreaks. However, their use has become more restricted due to the negative impacts they have on the environment, the host and humans, as well as their limitations in preventing the emergence of antimicrobial-resistant bacteria. Therefore, there is a growing interest in the use of medicinal plants and seaweeds as potential alternatives to antibiotics and other synthetic chemotherapeutics. Medicinal plants and seaweeds can enhance the immune systems of animals, thereby providing protection against numerous diseases while minimizing the adverse effects associated with synthetic chemotherapeutics. Furthermore, the advantages of medicinal plants and seaweeds, such as their effectiveness, easy availability and ability to be applied on a large scale, make them appealing for use in the aquaculture industry. The main goal of this study was to review the existing knowledge of the effects of medicinal plants and seaweeds, as well as their extracts, on shrimp growth, immune response and disease resistance against bacterial and viral agents. Moreover, this paper discusses the application of seaweeds in shrimp culture. We also conducted a literature review to identify gaps in the research and provide recommendations for further advancement in this field of study. Further studies should focus on evaluating other physiological aspects, such as feed and mineral utilization, enzyme activities and histological examination.

Dietary supplementation with succinic acid improves growth performance and flesh quality of adult Nile tilapia (Oreochromis niloticus) fed a high-carbohydrate diet

To evaluate the effects of dietary supplementation with succinic acid on growth performance, flesh quality, glucose, and lipid metabolism of Nile tilapia (Oreochromis niloticus) fed a high-carbohydrate diet (HCD), five iso-nitrogenous and iso-lipidic diets were prepared as follows: HCD (control group) consisting of 55% corn starch and HCD supplemented with 0.5%, 1.0%, 2.0%, and 4.0% succinic acid, respectively. Tilapia with an initial body weight of 204.90 ± 1.23 g randomly assigned to 15 tanks with 3 replicates per group and 10 fish per tank fed for 8 weeks. Increasing dietary succinic acid supplementation resulted in significant second-order polynomial relationship in the weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency rate (PER), viscerosomatic index, condition factor, and contents of muscular crude lipid and glycogen (P < 0.05). The hepatosomatic index, mesenteric fat index, liver glycogen content and crude lipid contents of the whole-body and liver demonstrated significantly linear and second-order polynomial relationship (P < 0.05). Quadratic curve model analysis based on WGR, SGR, PER, and FCR demonstrated that optimal supplementation with succinic acid in the HCD of Nile tilapia ranged from 1.83% to 2.43%. Fish fed with 1.0% succinic acid had higher muscular hardness, increased the contents of alkali-soluble hydroxyproline in collagen, docosahexaenoic acid (DHA) and n-3 polyunsaturated fatty acid (n-3PUFA) in muscle, and lower total fatty acid content in muscle (P < 0.05) compared with the control group. Compared to the control group, dietary supplementation with 1.0% succinic acid significantly increased the contents of total bounding amino acid (arginine, histidine, isoleucine, lysine, methionine, alanine, proline), total flavor amino acid (free aspartic acid), the catalase (CAT) activity and total antioxidant capacity, and the mRNA relative expression levels of CAT, superoxide dismutase (SOD), and nuclearfactor erythroidderived 2-like 2 (Nrf2) in muscle (P < 0.05). Furthermore, succinic acid supplementation significantly up-regulated mRNA relative expression levels of glycolysis genes (hexokinase 2 [HK2], phosphofructokinase, muscle-A [PFKMA], and phosphofructokinase, muscle-B [PFKMB]), a key glycogen synthesis gene (glycogen synthase [GYS]), and lipid catabolism genes (carnitine palmitoyltransferase-1B [CPT1B], hormone sensitive lipase [HSL], and lipoprotein lipase [LPL]), while down-regulating the mRNA relative expression level of fatty acid synthase (FASN) in muscle (P < 0.05). In conclusion, dietary supplementation with 1.83% to 2.43% succinic acid improved muscle quality by increasing muscle antioxidant capacity and hardness, changing muscle amino acid and fatty acid composition, and regulating muscle glucose and lipid metabolism.

Effects of Low-Salinity Stress on Histology and Metabolomics in the Intestine of Fenneropenaeus chinensis

Metabolomics has been used extensively to identify crucial molecules and biochemical effects induced by environmental factors. To understand the effects of acute low-salinity stress on Fenneropenaeus chinensis, intestinal histological examination and untargeted metabonomic analysis of F. chinensis were performed after exposure to a salinity of 15 ppt for 3, 7, and 14 d. The histological examination revealed that acute stress resulted in most epithelial cells rupturing, leading to the dispersion of nuclei in the intestinal lumen after 14 days. Metabolomics analysis identified numerous differentially expressed metabolites (DEMs) at different time points after exposure to low-salinity stress, in which some DEMs were steadily downregulated at the early stage of stress and then gradually upregulated. We further screened 14 overlapping DEMs, in which other DEMs decreased significantly during low-salinity stress, apart from L-palmitoylcarnitine and vitamin A, with enrichments in phenylalanine, tyrosine and tryptophan biosynthesis, fatty acid and retinol metabolism, and ABC transporters. ABC transporters exhibit significant abnormalities and play a vital role in low-salinity stress. This study provides valuable insights into the molecular mechanisms underlying the responses of F. chinensis to acute salinity stress.

Salicornia ramosissima Biomass as a Partial Replacement of Wheat Meal in Diets for Juvenile European Seabass (Dicentrarchus labrax)

The green tips of Salicornia ramosissima are used for human consumption, while, in a production scenario, the rest of the plant is considered a residue. This study evaluated the potential of incorporating salicornia by-products in diets for juvenile European seabass, partially replacing wheat meal, aspiring to contribute to their valorization. A standard diet and three experimental diets including salicornia in 2.5%, 5% and 10% inclusion levels were tested in triplicate. After 62 days of feeding, no significant differences between treatments were observed in fish growth performances, feeding efficiency and economic conversation ratio. Nutrient digestibility of the experimental diets was unaffected by the inclusion of salicornia when compared to a standard diet. Additionally, salicornia had significant modulatory effects on the fish muscle biochemical profiles, namely by significantly decreasing lactic acid and increasing succinic acid levels, which can potentially signal health-promoting effects for the fish. Increases in DHA levels in fish fed a diet containing 10% salicornia were also shown. Therefore, the results suggest that salicornia by-products are a viable alternative to partially replace wheat meal in diets for juvenile European seabass, contributing to the valorization of a residue and the implementation of a circular economy paradigm in halophyte farming and aquaculture.

Effects of Ammonia and Salinity Stress on Non-Volatile and Volatile Compounds of Ivory Shell (Babylonia areolata)

In this study, the flavor compounds of ivory shell (Babylonia areolata) and their changes caused by ammonia and salinity stresses were studied. Ammonia stress improved the contents of free amino acids (FAAs), 5'-adenosine monophosphate (AMP), citric acid, and some mineral ions such as Na+, PO43-, and Cl-. The FAA contents decreased with increasing salinity, while the opposite results were observed in most inorganic ions (e.g., K+, Na+, Mg2+, Mn2+, PO43-, and Cl-). Hyposaline and hypersaline stresses increased the AMP and citric acid contents compared to the control group. The equivalent umami concentration (EUC) values were 3.53-5.14 g monosodium glutamate (MSG)/100 g of wet weight, and the differences in EUC values among treatments were mainly caused by AMP. Hexanal, butanoic acid, and 4-(dimethylamino)-3-hydroxy- and (E, E)-3,5-octadien-2-one were the top three volatile compounds, and their profiles were significantly affected when ivory shells were cultured under different ammonia and salinity conditions.

Scutellaria polysaccharide mediates the immunity and antioxidant capacity of giant freshwater prawn (Macrobrachium rosenbergii)

The giant freshwater prawn (Macrobrachium rosenbergii) is a commercially valuable freshwater crustacean species that frequently appears a death affected by various diseases, resulting in substantial economic losses. Improving the survival rate of M. rosenbergii is a hot and essential issue for feeding the prawns. Scutellaria polysaccharide (SPS) extracted from Scutellaria baicalensis (a Chinese medicinal herb) is conducive to the survival rate of organisms by enhancing immunity and antioxidant ability. In this study, M. rosenbergii was fed 50, 100, and 150 mg/kg of SPS. The immunity and antioxidant capacity of M. rosenbergii were tested by mRNA levels and enzyme activities of related genes. The mRNA expressions of NF-κB, Toll-R, and proPO (participating in the immune response) in the heart, muscle, and hepatopancreas were decreased after four weeks of SPS feeding (P < 0.05). This indicated that long-term feeding of SPS could regulate the immune responses of M. rosenbergii tissues. The activity levels of antioxidant biomarkers, alkaline phosphatase (AKP), and acid phosphatase (ACP) had significant increases in hemocytes (P < 0.05). Moreover, catalase (CAT) activities in the muscle and hepatopancreas, as well as superoxide dismutase (SOD) activities in all tissues, significantly decreased after four weeks of culture (P < 0.05). The results demonstrated that long-term feeding of SPS could improve the antioxidant capacity of M. rosenbergii. In summary, SPS was conducive to regulating the immune capacity and enhancing the antioxidant capacity of M. rosenbergii. These results provide a theoretical basis for supporting SPS addition to the feed of M. rosenbergii.

3-Hydroxybutyrate helps crayfish resistant to Vibrio parahaemolyticus infection in versatile ways

The bacterial storage compound poly-β-hydroxybutyrate (PHB) is a potential bio-control agent in aquaculture. It has been reported that PHB benefit to the survival and growth, and improve their immunity of aquatic animals. However, the cellular and molecular regulation mechanisms of PHB in immunity process remain unclear. This study investigated the immune mechanism of hemocytes regulated by Halomonas-PHB (PHB-HM) and PHB monomer 3-HB. Red claw crayfish Cherax quadricarinatus was used as the experimental animal in cytological study. Fluorescence microscopy and flow cytometry (FCM) analysis indicated that PHB-HM labeled with fluorescein isothiocyanate (FITC) could be engulfed by granulocytes (Gs) and semi-granulocytes (SGs) upon in vitro incubation. Transmission electron microscopy (TEM) further showed the ongoing degradation of PHB granules inside Gs and SGs after the injection of PHB-HM into crayfish sinus, but phagocytosis of PHB-HM by hyalinocyte (H) was not observed. Therefore, Gs and SGs are considered the main effector cells of cellular immunity induced by PHB-HM, and SGs likely played a particular important role in this process. To study the biosafety and molecular mechanism of PHB monomer 3-HB, hemocyte viability and expression of the related genes were determined after being exposed to 0-1 mg/mL of 3-HB, and Vibrio parahaemolyticus (VP) was used as the pathogenic bacterium. The results confirmed that 3-HB had no toxic effect on hemocytes by means of cell viability assay, and supplementation with 1 mg/mL of 3-HB suppressed the growth rate of VP in TSB medium. Moreover, injection of 3-HB into the blood sinus of crayfish remarkably improved the phagocytic rate of Gs and SGs on VP. Furthermore, transcriptome assay was designed to illuminate the molecular mechanism of 3-HB regulation using red swamp crayfish Procambarus clarkii as experimental animals. RNA-seq analysis and qRT-PCR verification revealed that the microtubule and cytoskeleton-related genes were high expressed 3 h after 3-HB injection, indicating both genes might involve in building up the innate immunity. In summary, bacterial storage PHB could be phagocytosed by main effector blood cells and likely to be degraded within the cells. 3-HB helped the crayfish resistant to pathogens through improving phagocytosis, suppressing the growth of pathogenic bacteria, and increasing the expression of microtubule-related genes. The findings in this work provide cytological and molecular evidence which will facilitate the application of PHB and 3-HB as immune-control agents in farming of aquatic animals.

The associative induction of succinic acid and hydrogen sulfide for high-producing biomass, astaxanthin and lipids in Haematococcus pluvialis

To obtain higher yield of natural astaxanthin, the present study aims to develop a viable and economic induction strategy for astaxanthin production comprising succinic acid (SA) combined with sodium hydrosulfide (NaHS). The biomass (1.33 g L^-1), astaxanthin concentration (44.96 mg L^-1), astaxanthin content (163.55 pg cell^-1), and lipid content (55.34%) were achieved under 1.0 mM SA and 100 μM NaHS treatment. These results were concomitant with enhanced hydrogen sulfide (H₂S) but diminished reactive oxide species (ROS). Further study discovered that endogenous H₂S could improve astaxanthin and lipid coproduction under SA induction by mediating related gene transcript levels and ROS signalling. Additionally, the concentrations of biomass and astaxanthin increased to 2.14 g L^-1 and 66.25 mg L^-1, respectively, under the induction of SA and NaHS in a scaled-up bioreactor. Briefly, the work proposed a novel feasible strategy for high yields of biomass and astaxanthin by H. pluvialis.

Beneficial Changes in Growth Performance, Antioxidant Capacity, Immune Response, Hepatic Health, and Flesh Quality of Trachinotus ovatus Fed With Oedocladium carolinianum

The purpose of this study is to assess the feasibility of astaxanthin-rich Oedocladium carolinianum as an immunostimulant in the diet for Trachinotus ovatus. Three experimental diets containing 0% (OC0), 1% (OC1), and 5% (OC5) O. carolinianum powder were formulated for 6-week feeding trials. The results indicated that the OC5 diet boosted the growth performance through decreasing the feed conversion ratio and increasing digestive enzyme activities and intestinal villus length. Meanwhile, fish fed with the OC5 diet promoted antioxidant ability via stimulating the Nrf2-ARE signal pathway and enhancing antioxidant enzyme activities. Furthermore, the OC5 diet exerted hepatoprotective effects by suppressing the lipid deposition and inflammation response and enhancing the transport capacity of cholesterol. Besides, the OC5 diet improved the non-specific immunity by activating the lysozyme and complement system and increasing the nitric oxide content and total nitric oxide synthase activity. Dietary O. carolinianum supplementation promoted the deposition of astaxanthin in the whole body. Therefore, a diet supplemented with 5% O. carolinianum is recommended to boost the growth, antioxidant capacity, immune response, and flesh quality of T. ovatus.

Effects of Barranca yajiagengensis Powder in the Diet of Trachinotus ovatus on the Growth Performance, Antioxidant Capacity, Immunity and Morphology of the Liver and Intestine

Barranca yajiagengensis, a novel filamentous microalga, can accumulate lutein under high-light and low-nitrogen conditions. It is well known that lutein has antioxidant, anti-inflammatory and immune-modulating properties. The purpose of this study is to evaluate the effects of including lutein-rich B. yajiagengensis powder in the diet of Trachinotus ovatus on the growth performance, antioxidant capacity, immunity, liver, and intestinal morphology. For this aim, three experimental diets containing 0% (BY0), 1% (BY1), and 5% (BY5) B. yajiagengensis powder were formulated for six-week feeding trials. The results indicated that growth performance, feed utilization, and intestinal morphology were not affected by different diet treatments. Fish fed with the BY5 diet promoted antioxidant ability by activating the Nrf2-ARE signal pathway and enhancing antioxidant enzymes activities. Furthermore, the BY5 diet improved non-specific immunity and antibacterial ability by activating lysozymes and the complement system and increasing the nitric oxide (NO) content and total nitric oxide synthase activity. Dietary B. yajiagengensis supplementation improved the liver morphology and exerted hepatoprotective effects. Therefore, as a natural source of lutein, B. yajiagengensis has the potential as a safe and non-toxic immunostimulant for T. ovatus. A diet supplemented with 5% B. yajiagengensis is recommended to improve the growth, antioxidant capacity, immune response, and liver health of T. ovatus.

Dietary Succinate Impacts the Nutritional Metabolism, Protein Succinylation and Gut Microbiota of Zebrafish

Succinate is widely used in the food and feed industry as an acidulant, flavoring additive, and antimicrobial agent. This study investigated the effects of dietary succinate on growth, energy budget, nutritional metabolism, protein succinylation, and gut microbiota composition of zebrafish. Zebrafish were fed a control-check (0% succinate) or four succinate-supplemented diets (0.05, 0.10, 0.15, and 0.2%) for 4 weeks. The results showed that dietary succinate at the 0.15% additive amount (S0.15) can optimally promote weight gain and feed intake. Whole body protein, fat, and energy deposition increased in the S0.15 group. Fasting plasma glucose level decreased in fish fed the S0.15 diet, along with improved glucose tolerance. Lipid synthesis in the intestine, liver, and muscle increased with S0.15 feeding. Diet with 0.15% succinate inhibited intestinal gluconeogenesis but promoted hepatic gluconeogenesis. Glycogen synthesis increased in the liver and muscle of S0.15-fed fish. Glycolysis was increased in the muscle of S0.15-fed fish. In addition, 0.15% succinate-supplemented diet inhibited protein degradation in the intestine, liver, and muscle. Interestingly, different protein succinylation patterns in the intestine and liver were observed in fish fed the S0.15 diet. Intestinal proteins with increased succinylation levels were enriched in the tricarboxylic acid cycle while proteins with decreased succinylation levels were enriched in pathways related to fatty acid and amino acid degradation. Hepatic proteins with increased succinylation levels were enriched in oxidative phosphorylation while proteins with decreased succinylation levels were enriched in the processes of protein processing and transport in the endoplasmic reticulum. Finally, fish fed the S0.15 diet had a higher abundance of Proteobacteria but a lower abundance of Fusobacteria and Cetobacterium. In conclusion, dietary succinate could promote growth and feed intake, promote lipid anabolism, improve glucose homeostasis, and spare protein. The effects of succinate on nutritional metabolism are associated with alterations in the levels of metabolic intermediates, transcriptional regulation, and protein succinylation levels. However, hepatic fat accumulation and gut microbiota dysbiosis induced by dietary succinate suggest potential risks of succinate application as a feed additive for fish. This study would be beneficial in understanding the application of succinate as an aquatic feed additive.

Effect of garlic (Allium sativum) extract on growth, enzymological and biochemical responses and immune-related gene expressions in giant freshwater prawn (Macrobrachium rosenbergii)

In the current study, growth performance, biochemical constituents of muscle, activities of enzymes in the haemolymph, and expressions of immune-related genes were evaluated in the giant freshwater prawns Macrobrachium rosenbergii fed diets supplemented with aqueous garlic (Allium sativum) extract at 0, 5, 10 and 20 g/kg (w/w) for 60 days. At the end of the feeding trial, weight gain and specific growth rate were significantly improved in garlic-fed prawn groups compared with the control (p < 0.05). Moreover, feed conversion ratio was significantly lower in the garlic-fed groups than in the control (p < 0.05). Activities of catalase, superoxide dismutase and glutathione peroxidase in the hepatopancreas, activities of alanine aminotransferase, aspartate aminotransferase and levels of albumin and total protein in the hemolymph were significantly increased in the garlic treatments (p < 0.05). Furthermore, garlic supplemented diets improved muscle biochemical profiles, particularly contents of crude protein and total ash and upregulations of immune deficiency and heat shock proteins (HSP70) gene expression (p < 0.05). Therefore, garlic has positive effects on growth performance and physio-biochemical responses of M. rosenbergii, and thus, it can be used as an additive for stress resistance and as a growth promoter in sustainable aquaculture.

Adverse effects of dietary virgin (nano)microplastics on growth performance, immune response, and resistance to ammonia stress and pathogen challenge in juvenile sea cucumber Apostichopus japonicus (Selenka)

It has been well documented that micro- and nanoplastics are emerging pollutants in aquatic environments, and their potential toxic effects has attracted widespread concerns. Here, we evaluated the adverse effects of dietary polystyrene nanoplastics and microplastics (PS-N/MPs) on growth performance, oxidative stress induction, immune response, ammonia detoxification, and bacterial pathogen resistance of sea cucumber Apostichopus japonicus. After collection and acclimation, sea cucumbers were randomized into 3 groups (i.e., control, 100 nm PS-NPs and 20 µm PS-MPs at 100 mg kg^-1 diet) for 60-day feeding experiment. Every group contained 360 sea cucumbers which were equally divided into 3 aquaria as biological triplicates. The results showed that the specific growth rate and final weight of the sea cucumbers fed with diets containing PS-N/MPs were significantly lower than those of control group. Dietary virgin PS-N/MPs significantly increased the reactive oxygen species production and malondialdehyde content in coelomic fluid, causing oxidative stress and damage to the growth and development of A. japonicus. During the experiment, 100 nm PS-NPs significantly induced the depletion in cellular and humoral immune parameters. The calculated IBR values based on multi-level biomarkers revealed the size-dependent toxic differences of PS-NPs > PS-MPs. The relative expression levels of GDH and GS mRNA showed first rise and then fall trends after exposure to ammonia, and 100 nm PS-NPs had a more profound impact on suppressing ammonia detoxification compared with 20 µm PS-MPs. Moreover, the expression of Hsp90, Hsp70, CL, TLR, and CASP2 genes were all down-regulated by ammonia exposure. Taken together of IBR results, ammonia stress test and pathogen challenge, we deduced that dietary 100 nm PS-NPs are more potentially hazardous than 20 µm PS-MPs. These findings provide valuable information for understanding the size-dependent toxic effects of PS-N/MPs and early risk warning on marine invertebrates.

Effects of dietary tea tree oil on the growth, physiological and non-specific immunity response in the giant freshwater prawn (Macrobrachium rosenbergii) under high ammonia stress

This study aimed to investigate the effects of dietary tea tree oil (TTO) on the performance, intestinal antioxidant capacity, and non-specific immunity after ammonia nitrogen stress in Macrobrachium rosenbergii. Six experimental diets were formulated with 0, 25, 50, 100, 200, 400 mg/kg TTO, respectively. A total of 900 prawns (average initial weight, 0.39 ± 0.01 g) were randomly assigned to 6 groups in triplicate in 18 tanks. After an 8-week feeding trial, 20 prawns from each tank were changed with 20 mg/L ammonia stress for 24 h. The results showed that 100 mg/kg TTO significantly increased prawns performance and survival rate compared with the control group. Moreover, 100 and 200 mg/kg TTO significantly improved intestinal antioxidant capabilities by increasing SOD enzyme activities and decreasing MDA levels. In addition, the prawns fed with 100 mg/kg TTO diet showed the highest survival rate under ammonia stress. After ammonia stress, the group of 100 mg/kg TTO significantly improved antioxidant capacity by increasing hemolymph respiratory burst activity, as well as intestinal anti-superoxide anion activity and SOD. Coincidentally, 100 mg/kg TTO significantly upregulated the intestinal relative expression of antioxidant-related genes (peroxiredoxin-5). Further, it was found that 100 mg/kg TTO activated the toll-dorsal pathway in prawns, which performed the similar function as the classic NF-κB pathway by upregulating the TNF-α and IL-1. Finally, 100 mg/kg TTO increased the levels of iNOS activities and NO contents after ammonia stress and enhanced non-specific immunity. The results indicated that 100 mg/kg TTO could significantly improve the M. rosenbergii performance, antioxidant capacity and ammonia stress resistance. We suggested that the mechanisms may be attributed to that TTO enhanced the antioxidant capacity and non-specific immunity of M. rosenbergii via the NF-κB signal pathway.

Limosilactobacillus fermentum SWP-AFFS02 Improves the Growth and Survival Rate of White Shrimp via Regulating Immunity and Intestinal Microbiota

White shrimp Litopenaeus vannamei is an important species of farmed shrimp. Intestinal bacterial composition and immune activity play important roles in regulating the health condition of shrimp. Lactic acid bacteria Limosilactobacillus fermentum SWP-AFFS02 was isolated from the intestine of sea fish Rachycentron canadum, and the potential of its effect on growth, immunity, and intestinal microbiota of L. vannamei shrimp was investigated. Shrimps received feed with or without the addition of 8 log CFU/g L. fermentum SWP-AFFS02 thrice a day for 8 weeks. After 8-week treatment, weight gain, feed conversion rate, and survival rate of shrimp were greater in the L. fermentum SWP-AFFS02-feed group than in the control group. L. fermentum SWP-AFFS02 treatment increased the number of granular cells and semi-granular cells and decreased hyaline cell number when compared to the control group. L. fermentum SWP-AFFS02 promoted prophenoloxidase (PO) activity through increasing immune-associated gene expression in the hepatopancreas of shrimp. In addition, administration of feed containing L. fermentum SWP-AFFS02 regulated intestinal microbiota via decreasing the ratio of pathogenic bacteria, such as Vibrionaceae and Enterobacteriaceae, in the intestine of shrimp. This study demonstrated that administration of L. fermentum SWP-AFFS02 effectively prevented infection of L. vannamei shrimp by regulating intestinal microbiota and enhancing immunity in shrimp to increase the growth and improve their health status, which acted as a probiotic and provided beneficial effects on shrimp.

Reconstruction of Litopenaeus vannamei Genome-Scale Metabolic Network Model and Nutritional Requirements Analysis of Different Shrimp Commercial Varieties

As an important tool for systematic analysis, genome-scale metabolic network (GSMN) model has been widely used in various organisms. However, there are few reports on the GSMNs of aquatic crustaceans. Litopenaeus vannamei is the largest and most productive shrimp species. Feed improvement is one of the important methods to improve the yield of L. vannamei and control water pollution caused by the inadequate absorption of feed. In this work, the first L. vannamei GSMN named iGH3005 was reconstructed and applied to the optimization of feed. iGH3005 was reconstructed based on the genomic data. The model includes 2,292 reactions and 3,005 genes. iGH3005 was used to analyze the nutritional requirements of five different L. vannamei commercial varieties and the genes influencing the metabolism of the nutrients. Based on the simulation, we found that tyrosine-protein kinase src64b like may catalyze different reactions in different commercial varieties. The preference of carbohydrate utilization is different in various commercial varieties, which may due to the different expressions of some genes. In addition, this investigation suggests that a rational and targeted modification in the macronutrient content of shrimp feed would lead to an increase in growth and feed conversion rate. The feed for different commercial varieties should be adjusted accordingly, and possible adjustment schemes were provided. The results of this work provided important information for physiological research and optimization of the components in feed of L. vannamei.

Improvement of non-specific immunity, growth, and activity of digestive enzymes in Carassius auratus as a result of apple cider vinegar administration to diet

This study was conducted to evaluate the effects of apple cider vinegar (ACV) administration on non-specific immunity of serum and skin mucus, growth indices, and activity of digestive enzymes (amylase, lipase, and protease) in Carassius auratus. For this purpose, 180 fish (weighing 7.35 ± 0.19 g) were allocated to 4 treatment groups with 3 replications in a completely randomized design. Fish were fed for 105 days using a basal diet supplemented with 0% (control), 1% (T 1), 2% (T 2), and 4% (T 3) ACV (contained 5% acetic acid). Results showed a significant increase in lysozyme activity, ACH50, and total immunoglobulin of skin mucus in fish fed with T2 diet (p < 0.05). Total immunoglobulin and lysozyme activity were significantly lower in the serum of fish fed with control diet than those fed with the mentioned treatment (p < 0.05). The highest value was observed in fish fed with T2 diet. Minimum (p < 0.05) complement activity (1.52 ± 0. 25 U ml^-1) was observed in fish fed with control diet. The mean of the final weights (17.35 ± 1.39 g), daily growth (1.0 ± 0.01 g), and specific growth rate (2.19 ± 0.14) was significantly higher in T3 diet group than the controls (p < 0.05). While the highest amylase-specific activity was observed in the controls (p < 0.05), there was a significant increase in specific activity of protease, lipase, and alkaline phosphatase in T2 diet group (p < 0.05). According to the results of this study, the inclusion of a limited quantity of ACV (4%) into the diet can improve immunity and growth parameters in C. auratus.

Characterization and ACE Inhibitory Activity of Fermented Milk with Probiotic Lactobacillus plantarum K25 as Analyzed by GC-MS-Based Metabolomics Approach

Addition of probiotics to yogurt with desired health benefits is gaining increasing attention. To further understand the effect of probiotic Lactobacillus plantarum on the quality and function of fermented milk, probiotic fermented milk (PFM) made with probiotic L. plantarum K25 and yogurt starter (L. delbrueckii ssp. bulgaricus and Streptococcus thermophilus) was compared with the control fermented milk (FM) made with only the yogurt starter. The probiotic strain was shown to survive well with a viable count of 7.1 ± 0.1 log CFU/g in the PFM sample after 21 days of storage at 4°C. The strain was shown to promote formation of volatiles such as acetoin and 2,3-butanediol with milk fragrance, and it did not cause post-acidification during refrigerated storage. Metabolomics analysis by GC-MS datasets coupled with multivariate statistical analysis showed that addition of L. plantarum K25 increased formation of over 20 metabolites detected in fermented milk, among which γ-aminobutyric acid was the most prominent. Together with several other metabolites with relatively high levels in fermented milk such as glyceric acid, malic acid, succinic acid, glycine, alanine, ribose, and 1,3-dihydroxyacetone, they might play important roles in the probiotic function of L. plantarum K25. Further assay of the bioactivity of the PFM sample showed significant (p < 0.05) increase of ACE inhibitory activity from 22.3% at day 1 to 49.3% at day 21 of the refrigerated storage. Therefore, probiotic L. plantarum K25 could be explored for potential application in functional dairy products.

Cell metabolomics to study the cytotoxicity of carbon black nanoparticles on A549 cells using UHPLC-Q/TOF-MS and multivariate data analysis

Carbon black nanoparticles (CBNPs) are core component of fine particulate matter (PM2.5) in the atmosphere. It was reported that the particle in the atmosphere with smaller size and the larger the specific surface area are easier to reach the deep respiratory tract or even the alveoli through the respiratory barrier and cause lung injury. Therefore, it has been believed that ultrafine or nanometer particles with more toxic than those with larger particle sizes. Moreover, it was confirmed that CBNPs could induce inflammation, oxidative stress and changes in cell signaling and gene expression in mammalian cells and organs. However, the cytotoxicity mechanism of them has been uncertain so far. The aim of the present study was to explore the underlying mechanism of cytotoxicity induced by CBNPs on A549 cells. In the current research, the viabilities of A549 cells were detected by Cell Counting Kit-8 (CCK-8) assay. The further metabolomics studies were conducted to detect the cytotoxic effect of CBNPs on A549 cells with an IC50 value of 70 μg/mL for 48 h. Potential differential compounds were identified and quantified using a novel on-line acquisition method based on ultra-liquid chromatography quadrupole time-of-flight mass spectrometry(UHPLC-Q-TOF/MS). The cytotoxicity mechanism of CBNPs on A549 cells was evaluated by multivariate data analysis and statistics. As a result, a total of 32 differential compounds were identified between CBNPs exposure and control groups. In addition, pathway analysis showed the metabolic changes were involved in the tricarboxylic acid (TCA) cycle, alanine, aspartate and glutamate metabolism, histidine metabolism and so on. It is also suggested that CBNPs may induce cytotoxicity by affecting the normal process of energy metabolism and disturbing several vital signaling pathways and finally induce cell apoptosis.

RNA-seq revealed the signatures of immunity and metabolism in the Litopenaeus vannamei intestine in response to dietary succinate

The intestine is important for nutrition, metabolism and immunity. Succinate (SA) plays a vital role in the physiological homeostasis of animal intestines. However, the effects of dietary SA on the intestinal immunity and metabolism in shrimp are not clear. In this study, we investigated the immune and metabolic responses in the intestine of Litopenaeus vannamei that were fed diets consisting of different levels of SA: 0 g/kg (Con) and 10 g/kg (SA) for 56 days. The results from a RNA-seq analysis identified 6005 differentially expressed genes (DEGs), including 2728 upregulated genes and 3277 downregulated genes, which were grouped into 312 pathways. The DEGs were most enriched in pathways related to protein synthesis and amino acid metabolism, including "ribosome", "aminoacyl-tRNA biosynthesis", "pyrimidine metabolism", and "arginine and proline metabolism"; additionally, carbohydrate and lipid metabolism pathways were also activated. A large number of immune-related genes were associated with mucus barrier modification, antimicrobial activity, pathogen attachment and recognition, antioxidant activity, and apoptosis. The expression patterns of several candidate genes involved in the immune response and nutrition metabolism were detected by qPCR. This study provides insight into the transcriptomic modulating mechanisms associated with intestinal immunity and the metabolism of L. vannamei in response to the intake of dietary SA.

Effects of dietary anthocyanin on innate immune parameters, gene expression responses, and ammonia resistance of Nile tilapia (Oreochromis niloticus)

The present study investigated the effects of dietary anthocyanin on the growth performance, haematological, non-specific immune, and spleen gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 8.24 ± 0.64 g were used in the study; four of these were fed with diets incorporating anthocyanin (20 mg kg -¹, 40 mg kg^-1, 80 mg kg^-1 and 160 mg kg^-1), while the fifth was a control group without dietary anthocyanin. Growth performance and haematological parameters of tilapia were not affected by anthocyanin-supplemented diets (p > 0.05). Dietary anthocyanin significantly increased respiratory burst activity, phagocytic activity, phagocytic index, lysozyme activity, myeloperoxidase activity, serum total superoxide dismutase (T.SOD) activity, and serum catalase (CAT) activity (p < 0.05). The total immunoglobulin level was highest in the 80 mg kg^-1 group compared with the other groups (p < 0.05). In addition, with the anthocyanin-containing diets, the gene levels of interleukin 1, beta (IL-1β), interleukin 8 (IL-8), tumor necrosis factor (TNF-α), heat shock protein 70 (HSP70), and interferon gamma (IFN-γ) were increased in the fish spleen, and the gene levels of CAT, GPx, and SOD were also increased in fish liver (p < 0.05). At the end of the experiment, the fish were subjected to ammonia stress. The groups fed with 20 and 40 mg kg^-1 anthocyanin exhibited higher survival rates than the other groups. In summary, feeding Nile tilapia with anthocyanin-containing diets caused increases in the innate immune parameters, gene expression responses, and the survival rate of the fish subjected to ammonia stress.

Effects of lactic acid on drug-metabolizing enzymes in Chinese mitten crab (Eriocheir sisnensis) after oral enrofloxacin

Enrofloxacin (ENR) is the most commonly used antibiotic in crustacean farming in China. Diet supplementation with lactic acid (LA) may, however, affect the efficacy and safety of ENR-based drugs. The aims of this study were to investigate the effects of LA on drug residues and elimination of oral ENR in Chinese mitten crab (Eriocheir sinensis) and to determine ENR and gene expression levels of drug-metabolizing enzymes in the hepatopancreas. To this end, ENR was orally administered to the crabs at a dose of 10.0 mg kg^-1 body weight on the eighth day after feeding diets supplemented with 0.3%LA. The results showed that ENR levels in the hepatopancreas were significantly different at 1 and 12 h between the ENR and ENR + 0.3% LA groups (P < 0.05). Lactic acid did not significantly affect the expression of CYP2A (phase I). However, the expressions of CYP3 (phase I) and GST (phase II) were significantly up-regulated by LA during the elimination process of ENR (6-24 h). At T_max (1 h), the expression of phosphoenolpyruvate carboxykinase (PEPCK) was induced and expression of succinate dehydrogenase (SDH) was inhibited by LA. Both of these enzymes were significantly inhibited during the elimination process of ENR. The results suggest that LA contributes to the elimination of ENR, and thus, enhances hepatopancreas biotransformation and anti-injury capacity in E. sinensis.

Changes in the intestine microbial, digestion and immunity of Litopenaeus vannamei in response to dietary resistant starch

Resistant starch (RS) is a constituent of dietary fibre that has beneficial effects on the intestine physiological function of animals. However, the roles of RS on shrimp intestine health is unknown. In this study, we investigated the the effects of dietary RS on the microbial composition, and digestive and immune-related indices in the intestine of Litopenaeus vannamei. The shrimp were fed with diets containing different levels of RS: 0 g/kg (Control), 10 g/kg (RS1), 30 g/kg (RS2) and 50 g/kg (RS3) for 56 days. The results showed that dietary RS improved the morphology of the intestine mucosa. RS also increased the activity of digestive enzymes (AMS, LPS, Tryp, and Pep) and immune enzymes (PO, T-AOC, T-NOS, and NO), and the expression levels of immune-related genes (proPO, ALF, Lys, HSP70, Trx, Muc-1, Muc-2, Muc-5AC, Muc-5B, and Muc-19). A microbiome analysis indicated that dietary RS increased the short-chain fatty acids (SCFAs) contents and altered the composition of the intestine microbial. Specifically, RS increased the abundances of Proteobacteria and decreased the abundance of Bacteroidetes. At the genus level, the beneficial bacteria (Lutimonas, Ruegeria, Shimia, Mesoflavibacter, and Mameliella) were enriched, which might be involved in degrading toxins and producing beneficial metabolites; while potential pathogens (Formosa and Pseudoalteromonas) were decreased in response to dietary RS. Our results revealed that dietary RS could improve the intestine health of L. vannamei, probably via modulating the intestine microbial composition and SCFAs contents, and enhancing the digestion and immunity of the shrimp.

Effect of dietary supplementation with apple cider vinegar and propionic acid on hemolymph chemistry, intestinal microbiota and histological structure of hepatopancreas in white shrimp, Litopenaeus vannamei

This experiment was conducted to evaluate the effects of dietary supplementation of Apple cider vinegar (ACV) and propionic acid (PA) on biochemical parameters of hemolymph, intestinal microbiota and histology of hepatopancreas in white shrimp (Litopenaeus vannamei). Five experimental diets were evaluated in this study including diets supplemented with 1.0, 2.0 and 4.0% of ACV, 0.5% propionic acid, and a control diet with no supplements. Shrimps (initial weight of 10.2 ± 0.04 g) in triplicate groups with the density of 25 shrimps per tank were fed the diets for 60 days. At the end of the feeding trial, shrimps fed with ACV and PA supplemented diets had significantly higher total protein level than those fed the control diet (P < 0.05). The number of Vibrio spp., R-cells (lipid storage cells) of hepatopancreas and cholesterol level in shrimps fed the diets containing ACV and PA were lower compared to the control group (P < 0.05). However, there was no remarkable variations in glucose concentration, B-cell number and tubule diameter among the experimental diets (P > 0.05). In addition, shrimps fed the ACV diets had significantly lower total heterotrophic marine bacteria compared to the control or PA groups, and the lowest bacterial number was observed in shrimp fed 4% ACV supplemented diet (P < 0.05). Supplementation of 2 and 4% ACV as well as 0.5% PA in the diet led to a significantly higher calcium concentration than the control treatment (P < 0.05). The lowest triglyceride concentration was observed in the shrimps fed diets containing 2.0 and 4.0% ACV, which resulted in 15 and 20% reduction, respectively (P < 0.05). Overall, the findings indicates that ACV and PA possess antimicrobial activity and demonstrate beneficial effects on health status, so they can be potentially used as feed additive in the feeding of L. vannamei.

Effect of dietary alanyl-glutamine dipeptide against chronic ammonia stress induced hyperammonemia in the juvenile yellow catfish (Pelteobagrus fulvidraco)

Triplicate groups of juvenile yellow catfish (1.98 ± 0.01 g) were fed diets supplemented with 0% and 1% alanyl-glutamine dipeptide (AGD) for 56 days under three ammonia concentrations (0.01, 5.70 and 11.40 mg L^-1 total ammonia nitrogen). The results showed that ammonia poisoning could induce growth (weight gain and specific growth rate) and survival reduction, live ammonia and serum malondialdehyde accumulation, and subsequently lead to blood deterioration (serum total protein, albumin, globulin, alkaline phosphatase and acid phosphatase reduced), oxidative stress (superoxide dismutase and glutathione peroxidase activities declined), and induce down-regulation of antioxidant enzymes (SOD, GPX and GRX) genes transcription. However, dietary supplemented with 1% AGD could mitigate the adverse effect of ammonia poisoning on fish growth performance.