Total fish meal replacement with canola protein isolate in diets fed to rainbow trout (Oncorhynchus mykiss W.)

The potential of canola protein isolate (CPI) as fish meal alternative in diets for rainbow trout was evaluated. Apparent digestibility coefficients (ADCs) for protein from a fish meal-based reference diet (89.2 +/- 1.1%) and CPI (84.6 +/- 1.8%) were determined by indirect marker method in a digestibility experiment. ADC of dietary dry matter was slightly lower for the reference diet (62.5 +/- 4.7%), but not significantly different to the CPI test diet (65.9 +/- 3.1%). In a subsequent growth trial, 20 fish (initial weight 31.5 +/- 0.5g) were stocked into each of 15 experimental tanks of a freshwater flow-through system. Fish were organized in triplicate groups and received experimental diets with 0%, 25%, 50%, 75% and 100% of fish meal replaced with CPI on the basis of digestible protein (designated as Control, I25, I50, I75, I100 respectively). At the end of a 70-day feeding period, growth performance, feed intake and feed conversion ratio of treatment groups receiving diets I25, I50 or I100 were similar to the control group, while fish fed diet I75 showed significantly higher weight gain caused by improved feed conversion. The tested CPI was therefore identified to be a highly valuable fish meal alternative, not negatively affecting diet palatability, feed intake and feed efficiencies.