Albumin and globulin rapeseed protein fractions as fish meal alternative in diets fed to rainbow trout (Oncorhynchus mykiss W.)

The potential of two rapeseed protein concentrates partitioned in albumin and globulin fractions as fish meal alternative was evaluated. In a digestibility experiment with juvenile rainbow trout apparent digestibility coefficients (ADCs) were determined by indirect marker method with feces collected by continuous sieving. ADCs of protein from fish meal (89.2±1.1%) and globulin concentrate (88.8±0.6%) were significantly higher than ADCs from albumin concentrate (77.7±1.4%). ADCs of dietary dry matter were similar between the control diet (62.5±4.7%) and the globulin concentrate diet (62.3±0.5%), but significantly lower in the albumin concentrate diet (56.2±1.5%). In a subsequent growth trial, each of 21 experimental tanks of a freshwater flow-through system was stocked with ten rainbow trout (initial average weight 31.5±0.5g). Fish were organized in triplicate groups and received experimental diets with 0, 50, 75, or 100% of fish meal replaced with albumin (A50–100) or globulin (G50–100) concentrate on the basis of digestible protein. At the end of a 70day feeding period feed conversion ratio in the albumin treatment groups was not significantly affected at all substitution levels. But due to lowered feed intake at higher inclusion levels growth performance decreased at A 75 and A 100. Dietary globulin inclusion influenced growth performance by reduced feed intake and utilization in all groups negatively due to higher levels of glucosinolates and sinapinic acid. Significant lower fish survival rates were observed when fish received diets A75, A100, G50, G75, or G100 compared to the control diet or diet A50. For the whole body composition, the crude protein content was significantly lower in fish fed diet G75 or G100 compared to the control diet, while fish fed on diet A50, A75, or A100 were lower in body fat content than fish fed on the control diet. Thus, we demonstrated that the used albumin concentrate can effectively replace 50% of dietary fish meal in rainbow trout diets, whereas the application of the globulin concentrate negatively influenced diet palatability, thereby reducing diet intake and subsequently fish growth.