DIETARY SUPPLEMENTATION DURING PRODUCTION AND SURVEY OF MICRONUTRIENTS OF TILAPIA Oreochromis niloticus IN THE U.S. MARKETPLACE

Tilapia, (Oreochromis spp.) contributed to global production of 5, 576,800 MT in 2015. Due to high production there are extensive researches going on regarding nutrient requirements and alternative feed ingredients for Nile tilapia. However, limited research has been devoted to define the optimum micronutrient requirements for this species of fish. Selenium (Se) is a micronutrient that is of a great interest. By incorporating into group of Se containing proteins called selenoproteins this element plays a crucial role in varieties of biological processes. Gluthothione Peroxidase (GPx) is one of the main selenoproteins which is responsible of protecting cell membranes against oxidative damages. Antioxidant activity of Se in human has shown to be protective against 50 diseases (i.e. Kashan's disease) and can cause liver necrosis and thyroid problems. Se role in preventing oxidative stress and inducing apoptosis is particularly important for the aquaculture industry where immunocompetence and disease resistance can be compromised by intense culture environment. Also, fish fillet quality and shelf-life may be improved by the levels of antioxidant such as Se in pre-slaughter diet.

For these reasons, we conducted two studies. First study was a survey to evaluate the Se status of tilapia in the U.S. market. Market samples were also evaluated for the levels of As, Ca, Cd, Cu, Fe, Mb, Mn, Na, Pb, and Zn.  Second study was a fish trial to evaluate alternative sources of Se that can be used to enrich the tilapia fillet. The results from our survey study provided evidence that tilapia  fillets (n=12) in U.S. market has Se concentrations  of 0.94 ± 0.12 μ g^-1 .  A seven-weeks fish trial was conducted. Bioavailability of different forms of Se (organic and inorganic) in Nile tilpia (O. niloticus) was evaluated using uptake, tissue retention of Se and plasma and liver GPx activity. There was no significant difference between growth of fish fed different diets. However, organic Se fed fish fillets had Se levels of 2.6± 0.19 (μg g^-1) which were significantly (P<0.05) higher than inorganic Se fed fish (1.01± 0.01(μg g^-1)). Higher Se levels were found in liver and kidney compared to the fillet.  However, supplementation with any of investigated Se forms did not affect the GPx activity of liver and plasma. Inorganic source of Se is currently used in aquaculture diets. As expected, concentrations of Se in inorganic Se fed fillets was almost identical to market samples. This study shows that seleno-L-methionine (organic Se) is an excellent Se supplement to deliver a high level of Se in the fillet without causing harm to the fish. Organic species of Se should be used by the aquaculture industry as an alternative to inorganic species. Also, result of market study shows that tilapia in U.S.  market are good source of essential elements and do not pose any health risk problem to consumers.