Effects of the repartitioning agent ractopamine on the growth and body composition of rainbow trout Oncorhynchus mykiss (Walbaum), fed three levels of dietary protein
1998
Moccia, R.D. | Gurure, R.M. | Atkinson, J.L. | Vandenberg, G.W.
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 (approximately 16.6 MJ kg(-1)) practical diets supplying two levels of ractopamine (0 and 10 mg kg(-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) main effects of dietary protein were observed for MWT, SGR, CF, HSI, pigmentation, eviscerated-carcass ash, and visceral lipid and visceral ash content. Modest but significant (P < 0.05) interactions between ractopamine and protein were observed for HSI, pigmentation intensity and eviscerated carcass moisture content. The protein and lipid contents of both whole viscera and eviscerated carcasses were not affected (P > 0.05) by the inclusion of 10 mg kg(-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 10 mg kg(-1) of diet at the protein levels tested.
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