Abstract

Aquaculture is one of the world's fastest-growing food industries.¹ There is, however, an over-dependence on the use of prophylactic and therapeutic antibiotics in aquaculture, with a significant cost to human and environmental health (bacterial resistance, residues, toxicity).² Alternative products are being evaluated worldwide in the search for natural and cost-effective prophylactic supplements that can be incorporated into the fish diet.^3,4 IMUNO-2865® is a natural hemicellulose compound with well-documented immunostimulative properties in people, terrestrial and marine mammals.^5,6

The aim of this study was to test in vivo effects of IMUNO-2865® on blood parameters and oxidative stress responses in sea bream under aquaculture conditions. The research was conducted over a period of 6 months at a sea bream farm in Central Adriatic (Croatia). A total of 640 sea bream specimens (18 months old, weighing 277.8±38.0 g) were divided into four groups, placed in four 8 m³ net cages and conditioned for two weeks. Fish were fed with commercial pelleted food (Skretting) at a rate of 10 g dry diet/kg biomass/day. Four experimental diets containing 0 g (control group 1), 1 g (group 2), 10 g (group 3) and 25 g (group 4) of IMUNO-2865®/kg feed were prepared ahead of time and stored at 4°C. Samples were collected on days 0, 30, 60 and 90, after which the regular feeding regime was resumed at 15 g dry diet kg-1 biomass. A final sampling was performed on day 180 (90 days after consumption of the last experimental diet). No mortality was observed throughout the experiment. Although blood parameters fluctuated among sampling periods (e.g., erythrocyte counts were highest at the end of the experiment), no significant differences were noted among treatment groups for total number of erythrocytes, leukocytes, basophils, eosinophils, lymphocytes and thrombocytes. However, a significant increase (p < 0.05) in heterophil numbers was observed in group 4 compared to group 1 after 60 days, and an increase in monocyte number was observed in group 4 compared to the other groups after 30 days of feeding. Blood Ca⁺⁺ levels were significantly higher after 60 days of feeding in all treatment groups compared to the control, and remained elevated in group 4 even after 90 days following cessation of supplementation. Surprisingly, serum paraoxonase (PON1 in U/L) was elevated in the control group after 60 days compared to the treatment groups (p < 0.05). Glutathione peroxidase (GSH-Px) (U/L) and PON1 were significantly increased in groups 3 and 4 compared to the control group 90 days into the experiment. Superoxide dismutase (SOD) (U/L) was increased in group 4 compared to the control group from day 60 until the end of the experiment. Groups 2 and 3 also demonstrated increased SOD compared to the control after 90 days of supplementation (Figure 1).

Based on the cellular and oxidative stress parameters in the blood and lack of mortality, the results of this study suggest that the use of IMUNO-2865® in aquaculture has an overall positive and immunostimulative effect on sea bream during winter period of stress.

Figure 1 Differences in plasma Ca++ and oxidative stress enzymes (PON1, GSH-Px, SOD) between the control group (Group 1) and treatment groups (Groups 2, 3 and 4) supplemented with 0, 0.1, 1.0 and 2.5% of IMUNO-2865® in diet, respectively. Different letters indicate statistical significant differences between groups. Two-way ANOVA was used to test differences among groups and periods (p < 0.05) followed by Tukey post hoc test.

Acknowledgements

The authors express their gratitude to Animal Necessity, LLC for funding this research, and to the fish farm Dalmar-Croatia for providing technical support. Special thanks to our students Sara Basioli, Gabrijela Kustera and Marin Kolega for their help during the field work.

* Presenting author

Literature Cited

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