Effects of three beta adrenergic receptor agonists on growth performance, blood biochemical parameters, fatty acids composition and carnitine palmitoyltransferase I gene expression of rainbow trout Oncorhynchus mykiss

Different beta 1 and 2 adrenergic receptor agonists may be various biological and physiological effects on fish species. An experiment was designed to study the effects of feeding ractopamine, terbutaline and metaproterenol; as beta1, beta2 and less selective beta 2 adrenergic receptor agonists, respectively; on body weight gain, feed conversion ratio, concentration of biochemical parameters in the serum, gene expression of carnitine palmitoyltransferase I in liver and meat and also, fatty acids profile of filet meat of the rainbow trout. One hundred ninety two of juvenile rainbow trout were randomly assigned to 16 fiber glass tanks and fed one of four dietary treatments containing control (0), ractopamine, terbutaline and metaproterenol at levels of 10 ppm in diet for 8-week feeding trials. It was found that metaproterenol and ractopamine improved final body weight, body weight gain and feed conversion ratio of fish. The serum concentrations of phosphorus and albumin were also significantly increased by all beta adrenergic agonists and ractopamine reduced triglyceride level (p<0.05). The fatty acids level of fish filet was significantly increased by the dietary supplement of various beta adrenergic agonists (p<0.05) but ractopamine had a greater effect. The gene expression of carnitine palmitoyltransferase I in liver was significantly (P<0.05) increased by all beta adrenergic agonists. The present study showed that various beta1 and beta 2 adrenergic receptor agonists had same physiological effects on rainbow trout but it seems ractopamine, as a beta 1 adrenergic receptor, had more potential on fatty acid metabolism and growth response of rainbow trout.