Effect of Dietary Vitamins A and E on Whole Body and Liver Vitamin Concentrations in Rainbow Trout (Onchorhynchus mykiss)
Rainbow trout (Onchorhynchus mykiss; n=16–24 individuals per tank) were maintained on pelleted diets, in a closed recirculating water system at 13–15°C. Experimental diets contained either 22,000 or 220,000 IU vitamin A per kg dry matter (DM), and vitamin E concentrations of 18, 180, or 1800 IU/kg DM (n=3 replicates per dietary treatment). Intake (approximately 2% live weight), growth, and feed conversion were calculated weekly. After 8 weeks, fish were sacrificed, measured, and weighed. Livers were excised and weighed separately, and pooled liver and carcass homogenates were analyzed with standard tissue HPLC techniques to determine vitamin A and E concentrations. Dietary concentrations of vitamins A and E influenced both carcass and hepatic levels of these nutrients, although not to the same degree. A 10-fold increase in vitamin A resulted in a 10-fold increase in carcass vitamin A content (5.8±1.3 vs. 69.0±18.0 IU/g) and hepatic vitamin A concentration (27.7±1.42 vs. 393.3±157.1 IU/g). Similar increases in vitamin E content were noted in hepatic samples (49.5 to 365.6 to 3791.3 µg/g), while carcass concentration increased in a nonlinear fashion (8.8 to 28.1 to 257.5 µg/g). We saw no evidence of nutrient antagonisms at the concentrations fed. Clearly, fat-soluble vitamin concentrations in rainbow trout tissues can be altered by dietary manipulation. Such manipulation may be useful in formulating fish-based diets with known nutrient content, for use in applied feeding programs for piscivorous species.