Antimicrobial effect of the Biotronic® Top3 supplement and efficacy in protecting rainbow trout (Oncorhynchus mykiss) from infection by Aeromonas salmonicida subsp. salmonicida

Time effect of experimental infection on Rainbow trout (Oncorhynchus mykiss) by immersion with Aeromonas salmonicida subsp. salmonicida

Furunculosis caused by Aeromonas salmonicida subsp salmonicida (Ass) is a medically and economically important bacterial disease in salmonid farms that requires therapeutic measures to prevent and control the disease. Evaluation of the effectiveness of traditional measures such as antibiotics or vaccines usually requires infecting fish experimentally. The objective of this study is to develop a method of infectious challenge of large (250-g) Rainbow trout by immersion close to natural infection conditions. We compare mortality, morbidity and anti-Ass antibody production of Rainbow trout following different bathing times (2, 4, 8 and 24 h) at a final bacterial concentration of 10⁶ CFU/mL. One hundred sixty fish divided in five groups corresponding to the 4 bathing times and the non-challenged group were studied. The 24 h contact duration resulted in the infection of all fish, with a mortality rate of 53.25%. The challenged fish developed acute infection with symptoms and lesions (inappetance, altering of swimming behaviour, presence of boils) similar to those observed in furunculosis, and produced antibodies against the bacterium at 4 weeks after challenging, in contrast with the non-challenged group.

Modulation of gut microbiota, blood metabolites, and disease resistance by dietary β-glucan in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Prebiotics are known to have a positive impact on fish health and growth rate, and β-glucans are among the most used prebiotics on the market. In this study, rainbow trout (Oncorhynchus mykiss) were treated with a β-1,3;1,6-glucan dietary supplement (at a dose of 0 g, 1 g, 10 g, and 50 g β-glucan per kg of feed). After 6 weeks, the effect of the β-glucan was evaluated by determining the changes in the microbiota and the blood serum metabolites in the fish. The impact of β-glucan on the immune system was evaluated through a challenge experiment with the bacterial fish pathogen Yersinia ruckeri.

RESULTS

The microbiota showed a significant change in terms of composition following β-glucan treatment, notably an increase in the relative abundance of members of the genus Aurantimicrobium, associated with a decreased abundance of the genera Carnobacterium and Deefgea. Furthermore, analysis of more than 200 metabolites revealed that the relative levels of 53 metabolites, in particular compounds related to phosphatidylcholines, were up- or downregulated in response to the dietary supplementation, this included the amino acid alanine that was significantly upregulated in the fish that had received the highest dose of β-glucan. Meanwhile, no strong effect could be detected on the resistance of the fish to the bacterial infection.

CONCLUSIONS

The present study illustrates the ability of β-glucans to modify the gut microbiota of fish, resulting in alteration of the metabolome and affecting fish health through the lipidome of rainbow trout.

Effects of Dietary Supplementation with Green-Synthesized Zinc Oxide Nanoparticles for Candidiasis Control in Oreochromis niloticus

Zinc is an essential element for metabolism of Nile tilapia (Oreochromis niloticus). Nanomaterials have important benefits in aquaculture. The present study evaluated the effects of green-synthesized zinc oxide nanoparticles (ZnO-NPs) using Ulva fasciata extract as an anti-fungal agent against Candida albicans (C. albicans) in vitro and in vivo in O. niloticus. A total of 252 apparent healthy O. niloticus (20 ± 0.457 g/fish) were randomly allocated into six groups: The 1^st group fed on basal diet contaminated with C. albicans 15 × l0⁶ CFU/g diet, the 2^nd group fed basal diet only, the 3^rd and 5^th groups fed the basal diet supplemented with 40 or 60 mg/kg ZnO-NPs, respectively, and the 4^th and 6^th groups fed the basal diet contaminated with C. albicans 15 × l0⁶ CFU/g and concomitantly supplemented with 40 or 60 mg/kg ZnO-NPs, respectively. The experiment lasted for 8 weeks. The phyco-synthesized ZnO-NPs were characterized by XRD, UV-V, FTIR, TEM, and zeta potential. The anti-fungal activities of ZnO-NPs and the morphological changes to C. albicans cell due to ZnO-NPs were detected. The results revealed that dietary supplementation with the green-synthesized ZnO-NPs significantly improved the growth performance, survival, serum lysozyme activity, phagocytic activity, phagocytic index, respiratory burst activity, expression of immune-related genes (IL-1β, TGF, TNF-α), digestive enzyme activity, and histopathological finding in C. albicans-infected group, with a relative superiority to 40 mg/kg feed ZnO-NPs. It could be concluded that supplementing diets with 40 mg/kg of phyco-synthesized ZnO-NPs could be considered a better choice for controlling candidiasis in Nile tilapia.

Comparative study on the effect of dietary β-carotene and phycocyanin extracted from Spirulina platensis on immune-oxidative stress biomarkers, genes expression and intestinal enzymes, serum biochemical in Nile tilapia, Oreochromis niloticus

The current trial investigated the roles of β-carotene and phycocyanin extracted from Spirulina platensis on growth, serum biochemical, digestive enzymes, antioxidant defense, immune responses, and immune gene expression in Nile tilapia (Oreochromis niloticus). Fish (1.52 ± 0.10 g) were randomly stocked to three treatments with three replicates (12 fish per replicate) in nine aquaria (60 L glass aquarium for each), and reared for 70-days. Three tested diets were formulated to be isonitrogenous and isolipidic, and were offered for experimental fish until ad-libitum three times daily at 09:00 a.m., 11.00 a.m. and 3:00 p.m. The first diet (control) was without supplementation. About 50 mg β-carotene and 50 mg phycocyanin kg^-1 were supplemented to the other experimental diets, respectively. Results indicated that feed intake was not (P > 0.05) differ among experimental diets. Compared to control diet wight gain and specific growth rate were significantly (P < 0.05) in fish fed diet containing β-carotene, while, the highest weight gain and the best FCR were detected in phycocyanin diet. Survival fish among treatments was significantly (P < 0.05) differ and the highest survival rate was showed in fish fed diet supplemented with phycocyanin. Either β-carotene or phycocyanin significantly (P < 0.05) improved the intestinal digestive enzymes compared with control diet, where the highest values of chymotrypsin, trypsin, lipase and amylase were noticed in fish fed phycocyanin. Diets supplemented with β-carotene and phycocyanin significantly (P < 0.05) improved hematology parameters contents compared with to the control diet, and the best contents were detected in fish fed diet supplemented with phycocyanin. The highest significant (P < 0.05) phagocytic, lysozyme, immunoglobulin M (IgM), superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and total antioxidant capacity (T-AOC) activities were recorded in diet supplemented with phycocyanin. The transcripts of interferon gamma and interleukin 1β genes were (P < 0.05) up-regulated in the liver of fish fed diet supplemented with β-carotene and phycocyanin, but expression of HSP70 gene down-regulated in fish fed β-carotene and phycocyanin containing diet compared control. The highest gene expression of the interferon gamma and interleukin 1β was observed in fish fed phycocyanin.

Mycobacteriosis and Infections with Non-tuberculous Mycobacteria in Aquatic Organisms: A Review

The Mycobacteriaceae constitute a family of varied Gram-positive organisms that include a large number of pathogenic bacteria. Among these, non-tuberculous mycobacteria are endemic worldwide and have been associated with infections in a large number of organisms, including humans and other mammals and reptiles, as well as fish. In this review, we summarize the most recent findings regarding this group of pathogens in fish. There, four species are most commonly associated with disease outbreaks: Mycobacterium marinum, the most common of these fish mycobacterial pathogens, Mycobacterium fortuitum, Mycobacterium gordonae, and Mycobacterium chelonae. These bacteria have a broad host range: they are zoonotic, and infections have been reported in a large number of fish species. The main route of entry of the bacterium into the fish is through the gastrointestinal route, and the disease is associated with ulcerative dermatitis as well as organomegaly and the development of granulomatous lesions in the internal organs. Mycobacteriaceae are slow-growing and fastidious and isolation is difficult and time consuming and diagnostic is mostly performed using serological and molecular tools. Control of the disease is also difficult: there is currently no effective vaccine and infections react poorly to antibiotherapy. For this reason, more research is needed on the subject of these vexing pathogens.

Transcriptomic profile change, immunological response and disease resistance of Oreochromis niloticus fed with conventional and Nano-Zinc oxide dietary supplements

The present investigation was performed to evaluate the efficiency of Zinc oxide (ZnO) as a fish feed additive in immunomodulation of Oreochromis niloticus. Fish were fed on ZnO nano-particles (nZnO) and conventional (ZnO) in two concentrations (30 and 60 mg/kg diet), in addition to the control fish which was fed on Zn free diet. After 6° days, the highest survival rate was recorded in the nZnO₃₀ -supplemented group. The total antioxidant capacity (TAC) and antioxidant enzymes were improved in different dietary Zn supplementation, obviously in the nZnO₃₀ -supplemented group, while the lowest antioxidant status was noticed nZnO₆₀ supplemented fish. The lipid peroxides (MDA) level was diminished upon Zn supplementation, particularly in nZnO₃₀-supplemented group but showed a significant elevation in the nZnO₆₀-supplemented group. Furthermore, the immune parameters examined, lysozyme activity, bactericidal activity, and IgM were significantly higher in ZnO₆₀, and nZnO₃₀ supplemented groups. The C-reactive protein (CRP) level showed no significant increase in response to Zn supplementation in the both forms at level of 30 mg/kg diet, but showed marked elevation in nZnO₆₀- supplemented group. The mRNA expression profile of both interleukin 8 (IL-8), interleukin 1, beta (IL-1β) encoding genes showed an up-regulation that was found in all Zn- supplemented groups, but more pronounced in nZnO₆₀-supplemented group. On the other hand, the expression pattern of myxovirus resistance (Mx)-encoding gene showed no remarkable difference between the Zn- supplemented and control fish. The expression level of CXC-chemokine, toll-like receptor 7 (TLR-7), immunoglobulin M heavy chain (IgM heavy chain) and interferon gamma (IFN-γ) gene was upregulated in Zn-supplemented groups particularly in the nZnO₃₀- supplemented group. While, the lowest expression was found in nZnO₆₀- and ZnO₃₀-supplemented groups. Here, Zn supplementation promoted the immune and antioxidant strength in fish mainly in nano form at the level of 30 mg/kg diet but not at 60 mg/kg diet that disrupt the immune and antioxidant status and promote inflammatory response.

Effect of immunostimulatory feed supplements on the development of acquired immunity in rainbow trout (Oncorhynchus mykiss)

Immunostimulatory feed supplements are an increasingly common feature of aquaculture management and their benefit has been confirmed for a wide area of products. However, these investigations have often focused on the benefit of these supplements on the innate immune system. In the current project, we investigated a mixture of two commercial feed supplements (Biotronic^® Top 3 and Levabon^® Aquagrow E) with a known protective effect against bacterial infections. The effect of the supplemented diet on antibody titters of Oncorhynchus mykiss vaccinated against Yersinia ruckeri was determined by ELISA. Furthermore, an infection trial was performed to confirm the effect of the supplements on the survival of the fish. Finally, their effects on the growth parameters of the fish were also determined. The results from this study found no significant effect on the general antibody titters. However, when considering only the titters of specific anti-Y ruckeri antibodies, the supplemented feed was associated with an improved response to the vaccine, significantly better than in the fish that had received the control feed.