What They Did Back Then

* Master of Science completed 1992, University of Guelph

Advisor: Professor Richard D. Moccia

The effects of beta-adrenergic agonists on growth and metabolism in rainbow trout (Oncorhynchus mykiss).



Beta-adrenergic agonists are synthetic analogues of catecholamines that have been termed nutrient repartitioning agents. Beta-adrenergic agonists redirect energy from fat to protein deposition and improve growth performance of several domestic animal species. Responses of rainbow trout ( Oncorhynchus mykiss) to the beta-adrenergic agonists Cimaterol and Ractopamine were investigated in a series of acute and chronic feeding experiments. Although several metabolite concentrations, growth performance and carcass composition parameters were statistically different in treated versus control fish, the influence of beta-adrenergic agonist treatment on these parameters may not be biologically significant. In the acute study, fish were fed diets containing Cimaterol and serum was collected at subsequent, predetermined time intervals. Dietary Cimaterol at a level of 0.1 mg kg-1 BW increased serum glucose concentration and decreased the concentration of nonesterified fatty acids relative to controls. Growth performance, serum metabolite and growth hormone levels, and carcass composition were monitored in rainbow trout fed Ractopamine for 12 weeks. The growth rates of Ractopamine-fed fish were somewhat higher during the first 8 treatment weeks relative to controls, but were not different during the last 4 weeks. Feed efficiency was significantly ( P< 0.05) higher in fish fed 10 and 5 ppm Ractopamine compared to controls during weeks 1-4 and 4-8 respectively and was significantly higher ( P<0.05) in all treatment groups when averaged over the 12 week treatment period. Serum growth hormone was lower in fish treated for 4 weeks, and nonesterified fatty acid concentrations were higher in several Ractopamine-fed groups when compared to controls. Glucose was higher in all treated fish fed Ractopamine for 12 weeks. There was no consistent effect of Ractopamine on carcass fat but protein levels tended to be higher in fish fed Ractopamine for 8 weeks.

The results suggest that the growth and metabolism of rainbow trout can be modestly altered by dietary Cimaterol and Ractopamine, although many responses are not as consistent as those in mammals fed these beta-adrenergic agonists.