Effects of the repartitioning agent ractopamine on the growth and body composition of rainbow trout, Oncorhynchus mykiss (Walbaum), fed three levels of dietary protein

Abstract

Ractopamine is a synthetic catecholamine analogue which is known to affect the growth performance of both terrestrial and aquatic livestock species when it is incorporated into their feed. To investigate the effect of ractopamine on fish, rainbow trout, Oncorhynchus mykiss (Walbaum), (initial weight = 385.2 ± 1.4 g) were fed six iso-energetic (16.6 MJ kg−1) practical diets supplying two levels of ractopamine (0 and 10mgkg−1) at three levels of crude protein (CP; 25%, 35% and 45%) for 112 days. The mean weight gain (MWT), specific growth rate (SGR), condition factor (CF), viscerosomatic index (VSI), hepatosomatic index (HSI), muscle pigmentation intensity, and the proximate composition of eviscerated carcasses and viscera were measured at 28-day intervals up to day 112. There were no significant (P > 0.05) main effects of ractopamine on any of the responses measured. Significant (P & 0.05) by the inclusion of 10mgkg−1 ractopamine in the diet. These results indicate that ractopamine may not invoke the beneficial effects of enhancing protein accretion or reducing lipid content of rainbow trout when fed at 10mgkg−1 of diet at the protein levels tested.