Designing fish for improved human health status.

The time-course of accumulation of dietary organic and inorganic selenium (Se; 1.5 mg Se kg(-1) dry weight feed) was examined for muscle and hepatic tissues of hybrid striped bass (HSB) over 6 weeks. Animals, which had been fed a Se deficient diet for 2 months prior to study, were maintained in a recirculating life support system at 28 +/- 1 degrees C. PIT tagged fish were randomly assigned to one of 24 120 L aquaria (n = 5 per tank) and subsequently fed one of four diets: a fishmeal-based diet (control), soybean-casein-based feeds either supplemented with organic (SelPlex) or inorganic (sodium selenite) Se or as a basal diet, purposefully deficient in Se. Fish were fed twice daily on a 4% body weight basis. Samples taken at trial start (week 0), mid-way (3 weeks) and at trial end (6 weeks) included weight and length data, hepatosomatic (HSI) and visceral (VSI) indices, intraperitoneal fat (IPF) and muscle (MR) and feed conversion (FCR) ratios, serum protein (SP), hematocrit (PCV), and serum glutathione peroxidase (GP(x)) activity and muscle and heaptic Se concentrations. Survival was also monitored throughout the study. Muscle and hepatic Se levels increased in fishmeal and Se supplemented diets throughout the study. At trail end, greatest weight gain (P < 0.05) was observed in fish fed the control, fishmeal-based diet. Comparison of tissue Se levels indicated that the liver accumulated this mineral at greater concentrations than the muscle with highest levels being observed in the inorganic Se fed fish (P < 0.05). Se accumulation in control and inorganic Se fed fish was similar, whilst Se in the liver of fish fed the Se deficient diet was lowest among groups (P < 0.05). Muscle Se accumulation was found to be greatest in organic Se containing diets (P < 0.05), whereas the basal, Se deficient diet group, returned lowest levels (P < 0.05). Plasma GP(x) activity was similar in HSB fed the fishmeal and organic Se diets. The fishmeal fed group expressed higher (P < 0.05) GP(x) levels than that recorded for either the inorganic or basal diets. At trial end, no differences were recorded between groups for PCV or HSI, VSI or IPF. SP levels and MR were higher (P < 0.05) in fishmeal control fed fish. FCRs were lowest in fishmeal fed fish and highest for the Se deficient or basal diet. These studies demonstrate the feasibility of producing cultured fish with heightened levels of Se using simple dietary manipulations for 4-6 weeks or less before harvesting.