Chemical Composition and Preliminary Theoretical Estimates of Waste Outputs of Rainbow Trout Reared in Commercial Cage Culture Operations in Ontario

Twenty-eight rainbow trout Oncorhynchus mykiss and six feed samples were obtained from two cage culture operations in Ontario and analyzed by proximate analysis. This information was then used to estimate the waste outputs of rainbow trout cage culture operations. Calculations of nitrogen (N), lipid, phosphorus (P), and gross energy (GE) gains by the fish were based on the theoretical growth curve predicted by a thermal-unit growth coefficient model, and the N, lipid, P, and GE contents of the fish were estimated by regression analyses. The feed required to achieve the predicted growth and energy gain was calculated based on digestible energy requirements that were determined by modifying published Fish-PrFEQ bioenergetics models (assuming a 5% feed wastage). The theoretical digestible energy requirement of rainbow trout growing from 10 to 1,000 g reared in cages was estimated at 22.7 MJ/kg weight gain. Under these conditions, rainbow trout fed the various feed sampled were predicted to have feed conversion ratios (FCR = weight of food fed/weight gained) varying between 1.14 and 1.29. Total solid wastes were estimated to be between 240 and 318 kg/metric ton of fish produced, total N wastes between 47 and 71 kg, and total P wastes between 7.5 and 15.2 kg, the lowest values being representative of the two feeds most widely used by fish farms in Ontario.