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The physiological and immunological effects of astaxanthin on stressed Nile tilapia reared in a coupled-aquaponics system
Even though aquaculture may solve the world’s need for a substantial protein source, it also has its problems, with stress being the most significant issue. Stress causes a decrease in disease resistance. This causes fish to become more susceptible to bacterial infections and viruses, causing them to become ill. Because of stress, farmers experience a significant amount of financial loss every year. To treat the effects of stress on fish, antibiotics and other chemicals are used. The use of antibiotics and other chemicals in aquaculture are damaging ecosystems, increasing antibiotic resistance, and impacting human health. Nutraceuticals, food or food additivities with medicinal properties, are an alternative to using antibiotics and other chemicals. Astaxanthin (AST), a keto-carotenoid, has been shown to have strong antioxidant, anti-diabetic, anti-cancer, and immunomodulation properties, however effects of AST on the modulation of stress in fish has not been investigated extensively. The objective of this experiment was to investigate the effect of AST on the stress response of Nile tilapia (Oreochromis niloticus) by measuring the blood glucose, packed cell volume, spleen-somatic index, serum lysozyme activity, macrophage phagocytic capacity and condition factor. There were three experimental groups: control, stressed (hydrocortisone supplemented diet) and stressed treated with astaxanthin (hydrocortisone and AST supplemented diet). Fish were fed the designated diets over a month and sampled at day 0 and day 28 (4 weeks). There were only significant differences between the control and stressed groups for blood glucose and spleen-somatic index. These two parameters indicate that the fish in the stressed group were stressed. There were no significant differences between the stress and AST group and the stressed and groups. These data suggests that a diet supplemented with the current amount of AST (200 mg/kg of feed) is not able to modulate the stress response of Nile tilapia. Further research will need to be conducted to determine if AST will have a therapeutic effect on the stress response.