A novel herbal immunostimulant for rainbow trout (Oncorhynchus mykiss) against Yersinia ruckeri

Effect of diets containing probiotic yeast Cystobasidium benthicum and fruit Cyrtocarpa edulis on growth and immune parameters of Nile tilapia (Oreochromisniloticus)

This study investigates Cystobasidium benthicum (Cb) probiotic yeast and Cyrtocarpa edulis (Ce) fruit dietary effects, single (0.5 %) or combined (Cb:Ce, 0.25:0.25 %), on growth performance, humoral immunity in serum and skin mucus, and intestinal morphology of Nile tilapia (Oreochromis niloticus) after 14 and 28 days. The Cb group presented the highest (P < 0.05) specific growth rate, weight gain, and absolute growth rate with respect to the control group. Immunological assays indicated that Cb, Ce and Cb:Ce groups increased serum nitric oxide concentration compared to the control group (P < 0.05). Cb and Cb:Ce groups showed the highest serum myeloperoxidase enzyme activity at day 14 and 28, respectively (P < 0.05); whereas, Cb:Ce group had the highest (P < 0.05) myeloperoxidase activity in skin mucus. The superoxide dismutase enzyme activity was unaffected. On day 28, Cb, Ce, and Cb:Ce groups showed higher and lower (P < 0.05) catalase enzyme activity in serum and skin mucus, respectively, compared with the control group. Only the Cb group had higher (P < 0.05) total protein concentration in serum (day 14) and skin mucus (day 14 and 28) with respect to the control group. The lysozyme activity in serum (day 28) and skin mucus (day 14) was higher (P < 0.05) in the Cb group compared to the control group. Only the skin mucus of Ce group showed bactericidal activity against Aeromonas dhakensis (P < 0.05). Histological studies indicated that Cb and Cb:Ce groups increased microvilli height, and Cb, Ce and Cb:Ce augmented goblet cell area at day 14 compared to the control group (P < 0.05). At day 28, microvilli height was higher in all groups and the number of intraepithelial leukocytes increased in Cb and Ce groups with respect to the control group (P < 0.05). The ex vivo assay revealed that A. dhakensis in leukocytes decreased cell viability similar to the control group (P < 0.05). A principal component analysis (PCA) confirmed the results. In conclusion, C. benthicum in the diet was the best supplement to improve the growth and immunity of Nile tilapia.

New Evidence for the Role of Pituitary Adenylate Cyclase-Activating Polypeptide as an Antimicrobial Peptide in Teleost Fish

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is a multifunctional neuropeptide that is widely distributed and conserved across species. We have previously shown that in teleost fish, PACAP not only possesses direct antimicrobial properties but also immunomodulatory effects against the bacterial pathogens Flavobacterium psychrophilum and Pseudomonas aeruginosa using in vitro and in vivo experiments. These previous results suggest PACAP can be used as an alternative to antibiotics to prevent and/or treat bacterial infections in the aquaculture industry. To accomplish this goal, more studies are needed to better understand the effect of PACAP on pathogens affecting fish in live infections. In the present study, the transcripts PACAP, PRP/PACAP, and VPAC2 receptor were examined in rainbow trout (Oncorhynchus mykiss) naturally infected with Yersinia ruckeri, which exhibited an increase in their expression in the spleen when compared to healthy fish. Synthetic Clarias gariepinus PACAP-38 has direct antimicrobial activity on Y. ruckeri and inhibits up to 60% of the bacterial growth when the peptide is at concentrations between 50 and 100 µM in TSB. The growth inhibition increased up to 90% in the presence of 12.5 µM of PACAP-38 when salt-free LB broth was used instead of TSB. It was also found to inhibit Y. ruckeri growth in a dose-dependent manner when the rainbow trout monocyte/macrophage-like cell line (RTS11) was pre-treated with lower concentrations of the peptide (0.02 and 0.1 µM) before going through infection. Differential gene expression was analyzed in this in vitro model. Overall, the results revealed new evidence to support the role of PACAP as an antimicrobial and immunomodulatory peptide treatment in teleosts.

Dietary flaxseed (Linum usitatissimum) oil supplementation affects growth, oxidative stress, immune response, and diseases resistance in rainbow trout (Oncorhynchusmykiss)

This paper describes the effects of flaxseed (Linum usitatissimum) oil (FSO) as a feed additive on growth performance, oxidative stress, immunity, and disease resistance in rainbow trout (Oncorhynchus mykiss). Four-hundred-and-twenty rainbow trout individuals (mean weight: 25.66 ± 1.33 g) were fed with different doses of FSO (0.5, 1, and 1.5%) ad libitum two times a day for 9 weeks. At the end of the feeding, growth performance was evaluated and the fish were challenged with two different bacteria (Yersinia ruckeri and Aeromonas hydrophila). At the end of the 3rd, 6th, and 9th weeks, blood and tissue samples were collected from 9 fish per treatment to evaluate innate immune response, cytokine gene expression levels, antioxidant enzyme activities and lipid peroxidation levels, and digestive enzyme activities. Determination of haematological parameters and histological examination was also carried out to evaluate the general health status of the fish. Results showed that the final weight and specific growth rate of fish supplemented with FSO increased significantly (p < 0.05). FSO-supplemented fish showed higher resistance to Y. ruckeri infection than the control group (p < 0.05). However, survival rates of all groups in A. hydrophila challenge test were similar (p > 0.05). Among the investigated innate immune response parameters, the potential killing activity of phagocytes, myeloperoxidase activity, and lysozyme activity increased in the FSO-supplemented groups (p < 0.05). Almost all cytokine gene expression levels in the experimental groups up-regulated especially after 9 weeks of feeding in the head kidney and intestine (p < 0.05). Similarly, superoxide dismutase and catalase activities were found to be significantly higher in the FSO group than in the control (p < 0.05) whereas, the lipid peroxidation levels drastically declined as a result of the FSO supplementation (p < 0.05). These results suggest that FSO can improve growth, enhance immune response, and lower oxidative damage in rainbow trout when supplemented at the rates of 0.5-1.5% for 9 weeks.

Effect of dietary celery (Apium graveolens) on the growth performance, immune responses, and bacterial resistance against Vibrio anguillarum of European seabass (Dicentrarchus labrax)

In this study, we evaluated to reveal the effects of aqueous methanolic extract of celery (Apium graveolens) on the growth performance, immune responses, and resistance against Vibrio anguillarum in European seabass (Dicentrarchus labrax). For this purpose, twenty fish (initial mean weight of 4.80 ± 0.06 g) were placed into twelve tanks (400 L) in triplicate and fish were fed with control (C) and three different levels (0.01, 0.05, and 0.1 g/kg) of A. graveolens (AG) extract-containing diets (AG0.01, AG0.05, and AG0.1) for 30 days. Blood and tissue (kidney, spleen, and intestine) samples were taken from the fish every 10 days during the study to determine the immune responses of the fish. Respiratory burst activity (RBA) was significantly decreased in the AG0.1 group compared to all other groups on the 10th day of the study (P < 0.05). Significance was noticed in the RBA of fish in all AG groups compared to the C group (P < 0.05) on the 30th day of the experiment Lysozyme activity (LYS) was raised on the 10th day of the study in all celery groups compared to the C group (P < 0.05). No differences in the myeloperoxidase activity (MPO) were observed among the experimental groups (P > 0.05). The final mean weight (FMW) was not affected in any experimental groups (P > 0.05). However, in the AG0.05 group, the specific growth rate (SGR) increased, and the feed conversion ratio (FCR) decreased compared to other groups (P < 0.05). IL-1β in the kidney was highly elevated in the AG0.01 group on the 20th day of the study (P < 0.05). Similar results were observed on IL-6, IL-8, and TNF-α expression in the kidney (P < 0.05). Anti-inflammatory responses (IL-10 and TGF-β) also increased in all experimental groups and tissues compared to the C group (P < 0.05). COX-2 was upregulated on the 20th day of the study in all tissues (P < 0.05). At the end of the feeding trial, the survival rate of the AG0.1 group in fish infected with Vibrio anguillarum infection was higher than the C group. Dietary celery extract did not affect growth performance directly but increased innate immune responses and a high survival rate. Overall, compared to the control group, the growth, immunity, and resistance of European seabass fed with a diet containing 0.05 g/kg celery aqueous methanolic extract has been improved, and this could be used as an immunostimulant feed additive.

Effects of white mustard (Sinapis alba) oil on growth performance, immune response, blood parameters, digestive and antioxidant enzyme activities in rainbow trout (Oncorhynchusmykiss)

A study was conducted to evaluate the effects of dietary supplementation of white mustard (Sinapis alba) oil (WMO) on growth performance, immune responses, digestive and antioxidant enzyme activities in juvenile rainbow trout (Oncorhynchus mykiss). For this purpose, fish (initial weight: 25.77 ± 0.13 g) were divided into four experimental groups in triplicate and fed ad libitum twice a day with diets containing WMO at 0 (control), 0.5, 1, and 1.5% of diet for 9 weeks. Three fish from each tank (n:9 per treatment) were sampled on 21st, 42nd, and 63rd days for further analyses. At the end of the feeding period, fish were challenged with Aeromonas hydrophila and Yersinia ruckeri in two separate experimental setups. Results showed that final weight, weight gain, and specific growth rate were significantly increased in all experimental groups compared to the control. Feed conversion ratio was similar among treatments. Respiratory burst and potential killing activity decreased in all experimental groups compared to the control (P < 0.05). Lysozyme and myeloperoxidase activities were elevated in all experimental groups at the end of the experiment compared to the control (P < 0.05). Cytokine gene expressions in the head kidney and intestine were elevated in all experimental groups compared to that of the control in general (P < 0.05). Hematological responses of the experimental fish groups were similar to that of the control (P > 0.05). Pepsin and trypsin levels decreased in all experimental groups (P < 0.05). In terms of antioxidant enzyme activities, significant improvement in liver superoxide dismutase, catalase, and glutathione s-transferase activities in all treatment groups were determined (P < 0.05). In addition, a significant decline in liver lipid peroxidation levels was recorded in all treated groups at all sampling times compared to the control (P < 0.05). At the end of this feeding trial, no significant differences (P > 0.05) were observed in survival against A. hydrophila among experimental groups compared to the control (P > 0.05). However, increased survival against Y. ruckeri was determined in experimental fish groups (P < 0.05). This study suggests that white mustard oil had a favorable effect on the overall health and growth of rainbow trout.

Impact of dandelion polysaccharides on growth and immunity response in common carp Cyprinus carpio

Natural products have gained considerable attention for improving fish growth performance and immunity to enhance disease resistance. This study evaluated the effect of dandelion polysaccharides (DP) on skin mucosal immune parameters, immune-related gene expression, and susceptibility to pathogen challenge in the Common carp Cyprinus carpio. Diets containing four different concentrations of DP (g Kg^-1):0 g [basal diet], 0.5 g [D1], 1.5 g [D2], 2.5 g [D3], and 4.0 g [D4] were fed to the carp (average weight: 13.92 ± 0.83 g) for eight weeks. Growth parameters were analyzed four and eight weeks after feeding. Immunological, hematological, and antioxidant parameters were examined eight weeks post-feeding. Growth performance was significantly higher on D3, with a final weight gain of 71.48 ± 1.57 g and a specific growth rate of 3.06 ± 0.12. Among hematological parameters examined, erythrocyte^, hematocrit, and mean corpuscular volume (MCV) levels were significantly higher in D3. Skin mucosal immune parameters, such as lysozyme (31.04 ± 1.02 Unit mL^-1), alkaline phosphatase (122.6 ± 3.8 IU L^-1), and protein level (10.6 ± 0.74 mg mL^-1) were significantly higher in D3, while peroxidase activity was higher in D4. Furthermore, SOD activity was higher in D2-D3, whereas catalase activity was higher in D2-D4 (P < 0.05) than in the control. Malondialdehyde level decreased significantly in D3 (5.43 ± 0.36 nmol mL^-1); whereas, serum ALT and AST levels were significantly lower on D2-D4. Intestinal tight-junction-related genes ZO-1 and Claudin 7 were significantly higher in the DP-fed groups; however, DP had no significant effect on claudin 3. Occludin expression was higher (p < 0.05) on D3 only. Pro-inflammatory cytokines (IL-1β and TNF-α) and IFN-γ strongly upregulated in the head kidney at D3. Conversely, the expression of the anti-inflammatory cytokine interleukin-10, HSP70, and TOR were considerably downregulated in D3. Fish from D3 exhibited markedly higher relative post-challenge survival (66.67%) against Aeromonas hydrophila challenge. The results of the present study suggest that dietary supplements of DP at 2.5 g kg^-1 can significantly improve the growth performance, skin mucosal, and serum antioxidant parameters, and strengthen the immunity of C. carpio. Therefore, DP is a promising food additive for carp aquaculture.

Effect of microplastics on Yersinia ruckeri infection in rainbow trout (Oncorhynchus mykiss)

Exposure to microorganisms such as Yersinia ruckeri can significantly affect bacterial infections in fish. Microplastics (MPs) may predispose fish to infection and act as carriers in pathogen transmission. Therefore, this study is designed to evaluate MPs' effect on damage caused by exposure to Y. ruckeri in rainbow trout. In this study, blood biochemical parameters and hepatic oxidative biomarkers as clinical signs were measured in the fish co-exposed to Y. ruckeri (5 and 10% the median lethal dose (LD₅₀)) and MPs (500 and 1000 mg Kg^-1) for 30 days. There were no significant changes in the creatinine, triglyceride, cholesterol levels, and glutamic-pyruvic transaminase activity in the blood of fish infected with Y. ruckeri. In contrast, exposure to MPs had a significant effect on most clinical parameters. The total protein, albumin, globulin, total immunoglobulins, high-density lipoprotein, low-density lipoprotein, cholesterol levels, and γ-glutamyltransferase activity decreased, whereas glucose, triglyceride, and creatinine levels, and glutamic-oxaloacetic transaminase, glutamic-pyruvic transaminase, alkaline phosphatase, and lactate dehydrogenase activities increased in the plasma of fish after co-exposure to MPs and Y. ruckeri. Dietary MPs combined with a Y. ruckeri challenge decreased catalase and glutathione peroxidase activities, and total antioxidant levels. However, superoxide dismutase activity and malondialdehyde contents increased in the hepatocyte of fish co-exposed to MPs and Y. ruckeri. This study suggests that fish exposure to MPs and simultaneous challenge with Y. ruckeri could synergistically affect clinical parameters.

Gut Immune System and the Implications of Oral-Administered Immunoprophylaxis in Finfish Aquaculture

The gastrointestinal immune system plays an important role in immune homeostasis regulation. It regulates the symbiotic host-microbiome interactions by training and developing the host's innate and adaptive immunity. This interaction plays a vital role in host defence mechanisms and at the same time, balancing the endogenous perturbations of the host immune homeostasis. The fish gastrointestinal immune system is armed with intricate diffused gut-associated lymphoid tissues (GALTs) that establish tolerance toward the enormous commensal gut microbiome while preserving immune responses against the intrusion of enteric pathogens. A comprehensive understanding of the intestinal immune system is a prerequisite for developing an oral vaccine and immunostimulants in aquaculture, particularly in cultured fish species. In this review, we outline the remarkable features of gut immunity and the essential components of gut-associated lymphoid tissue. The mechanistic principles underlying the antigen absorption and uptake through the intestinal epithelial, and the subsequent immune activation through a series of molecular events are reviewed. The emphasis is on the significance of gut immunity in oral administration of immunoprophylactics, and the different potential adjuvants that circumvent intestinal immune tolerance. Comprehension of the intestinal immune system is pivotal for developing effective fish vaccines that can be delivered orally, which is less labour-intensive and could improve fish health and facilitate disease management in the aquaculture industry.

Effect of Pandanus tectorius extract as food additive on oxidative stress, immune status, and disease resistance in Cyprinus carpio

The present study investigated the effect of Pandanus tectorius (PT) extract on Cyprinus carpio growth, antioxidant capacity, immunological and oxidative stress, immune-related gene expression, and resistance against pathogen challenge. Fish (average weight: 12.18 ± 0.32 g) were fed with diets containing various concentration (g kg^-1) of PT extract: 0 g (basal diet), 5 g [PT5], 10 g [PT10], 20 g [PT20], and 30 g [PT30] for 8 weeks. Our results revealed an increase (p < 0.05) in the final weight gain only in the PT20 (63.12 ± 1.4 g) group. Activity of liver antioxidant parameters such as catalase (CAT) (27.67 ± 1.12 U mg protein^-1), superoxide dismutase (SOD) (13.17 ± 0.428 U mg protein^-1), and glutathione peroxidase (GPx) (47.14 ± 1.47 U mg protein^-1) was highest in the PT20 group. Among the serum immunological parameters examined, lysozyme (37.45 ± 0.67 U mL^-1), alternative complement pathway (133.22 ± 1.92 U mL^-1), and phagocytic activities (25.68 ± 0.93%) were high (p < 0.05) in PT20, whereas there was no significant effect on serum immunoglobulin or total protein levels, compared to the control. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and malondialdehyde (MDA) levels were found to be lower (p < 0.05) in the PT20 and PT30 groups than those in the control. However, myeloperoxidase (MPO) levels were significantly higher (p < 0.05) in the PT20 and PT30 groups. Gene expression analysis revealed that mRNA expressions of antioxidant genes (SOD, CAT, nuclear factor erythroid 2-related factor 2) and anti-inflammatory cytokine (IL-10) genes were significantly upregulated in the PT10 - PT30 groups, except for the SOD gene in PT10. Conversely, the signalling molecule NF-κBp65 was downregulated in PT20 and PT30. Expression of Toll-like receptor 22 (TLR22) and hepcidin was significantly upregulated in PT20 and PT30, respectively. Fish in the PT20 group exhibited highest relative post-challenge survival (70.37%) against Aeromonas hydrophila challenge. The results of the present study suggest that dietary supplementation of P. tectorius extract at 20 g kg^-1 can significantly improve weight gain, serum antioxidant parameters, strengthen immunity, and increase the disease resistance of C. carpio. Therefore, P. tectorius extract could be exploited for its use as a food additive in aquaculture.

β-glucan as a promising food additive and immunostimulant in aquaculture industry

The use of antibiotics in aquatic feed reduces the incidence of disease and enhances growth performance, although it presents harmful effects, such as development of resistant bacteria and accumulation in the natural environment. A variety of immune stimulants including probiotics, prebiotics, synbiotics, phytobiotics, organic acids, nucleotides, antioxidants, microalgae, yeast and enzymes have been used in the aquaculture industry. In recent decades, much attention has been paid on finding a variety of immunostimulants with lower cost which also affect specific and non-specific immunity and improve fish resistance against a wide range of pathogens. These stimulants strengthen the fish’s immune system by increasing the number of phagocytes, lysozyme activity and level of immunoglobulin. The use of immune stimulants as an effective tool to overcome diseases and strengthen the immune system of farmed species, leads to the promotion of cellular and humoral defense mechanisms and increases resistance to infectious diseases. Among these immunostimulants used in aquaculture, β-glucans are of particular importance. Glucans are complex polysaccharide compounds extracted from the cell wall of yeasts and fungi. These compounds can stimulate fish growth, survival, and immune function. Therefore, this review discusses the role and importance of β-glucan as a food additive in aquaculture and examines the impact of these compounds on the growth performance, immunity and biochemical parameters of farmed species.

Modulatory effects of laurel-leaf cistus (Cistus laurifolius) ethanolic extract on innate immune responses and disease resistance in common carp (Cyprinus carpio)

Medicinal herbs are used for growth promotion, disease control and other health benefits in aquaculture industry. Here, we examined the effect of dietary laurel-leaf cistus (Cistus laurifolius) ethanolic extract on growth performance, digestive enzyme activity, haematological profile and nonspecific immune responses in common carp (Cyprinus carpio). In addition, resistance against Aeromonas hydrophila infection was examined. Common carp was fed diets containing 0 (Control), 0.1 (CL0.1), 0.5 (CL0.5) and 1 (CL1) g kg^-1 laurel-leaf cistus extract for 45 days. After 30 days, superoxide anion production (SAP) increased in CL0.1 and CL0.5 fish groups and at the end of the study all experimental fish groups had higher SAP compared to that of the control (P ˂ 0.05). Lysozyme activity (LA) was elevated in CL0.5 and CL1 treated groups on 30th day (P < 0.05), and this increase was only observed in C0.1 fish group at the end of study compared to control (P ˂ 0.05). Myeloperoxidase activity was significantly increased in CL0.5 and CL1 fish groups at the end of study. IL-1βgene expression was significantly increased in treated fish in a dose-depended manner. Similar results were observed for transcription of IL-6 and IL-8 (P < 0.05). Anti-inflammatory cytokines, IL-10 and TGF-β were highly up-regulated in the intestine and head kidney of CL treated fish groups compared to control (P < 0.05). At the end of experiment, significantly higher final body weight, weight gain, and specific growth rate were obtained in CL0.1 treated fish group compared to control. However, growth was negatively affected in CL1 fish group (P < 0.05). CL1 fish group had also a significantly higher FCR. Amylase activity was significantly increased in all experimental fish groups compared to control (P ˂ 0.05). Trypsin activity was decreased in CL0.1 and CL1 fish groups (P ˂ 0.05). WBC and RBC were significantly increased (P ˂ 0.05) in CL0.5 and CL1 fish groups, whereas haemoglobin, haematocrit, mean cell, mean cell haemoglobin contents were no significantly changed among control and treatment groups. Result of challenge test with A. hydrophila exhibited that survival rate in all treatment groups was significantly higher than that of control. These findings demonstrated that laurel-leaf cistus at 0.1 g kg^-1 can be a suitable candidate for growth promotion, immune system induction and infection control in fish.

Antioxidant enzyme activities and immune responses in rainbow trout (Onchorhynchus mykiss) juveniles fed diets supplemented with dandelion (Taraxacum officinalis) and lichen (Usnea barbata) extracts

In the present study, antioxidant activity, immune responses, and growth performance of rainbow trout (Onchorhynchus mykiss) juveniles fed with diets supplemented with dandelion (Taraxacum officinalis) and lichen (Usnea barbata) extracts were assessed. Four different concentrations of aqueous methanolic extract of the plants (0% (control), 0.1%, 0.5%, and 1% (D, dandelion; L, lichen) were added to the diets, and fish were fed for 75 days. On the 15^th, 45^th, and 75^th day of the study, liver antioxidant enzyme activities were determined, and immune responses were determined every 15^th day. The results showed that SOD activity increased in the fish group of 0.1% D on the 15^th and 45^th day compared to control; however, it was lower in all the lichen extract-treated groups than in control at almost all sampling times, except on the 15^th day in the 0.1% L group. CAT activity showed an increased value (P < 0.05) in 0.5% L and 1% L treated fish groups on the 15^th day, in fish of 1% D and 1% L groups on 45^th and on 75^th day in 0.1% D group. GPX activity increased on the 15^th day of the study in fish of 0.1% D group, on the 45^th day in 1% D and 1% L groups and on the 75^th day in fish of 0.5% D, 0.1% D, and 0.5% L groups (P < 0.05). G6PDH enhanced in all treatment groups compared to control on the 15^th day, except in 0.1% L and 0.5% L groups. An elevated G6PDH activity was also observed on the 75^th day of the study in 0.5% D, 1% D, and 0.5% L fish groups. An increase on lipid peroxidation (LP) was observed in all L groups on the 45^th day of the study. Lysozyme activity was determined to be the highest in 0.5% and 1% L on the 45^th day, in 0.1% L on the 60^th day and in the 0.5% L fish group on the 75^th day compared to control (P < 0.05). Myeloperoxidase was found to be the highest at the end of the study in 1% L fish group compared to the control (P < 0.05). In conclusion, we suggest the use of dandelion to combat oxidative stress and to lower FCR and the use of lichen to modulate the immune response in rainbow trout. The use of such products will be economical for aquaculture and harmless for the environment.