Dietary influence of replacing fish meal and oil with canola protein concentrate and vegetable oils on growth performance, fatty acid composition and organochlorine residues in rainbow trout (Oncorhynchus mykiss)

An experiment was performed to examine the effect of replacing fish meal and fish oil with canola protein concentrate and 65:35 mixture of canola and linseed oil on growth performance and carcass composition (fatty acids, polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/F) and dioxin-like polychlorinated biphenyls (DL-PCB)) of rainbow trout. Thirty tanks of rainbow trout (n = 20/tank) were randomly assigned to one of 5 diets. The control diet contained 400 g kg− 1 fish meal and 200 g kg− 1 fish oil (FO/FM100) and the 4 experimental diets all contained 200 g kg− 1 of a 65:35 mixture of canola:linseed oil and 400 (VO/FM100), 200 (VO/FM50), 100(VO/FM25) or 0 (VO/FM0) g kg− 1 of fish meal replaced by canola protein concentrate on an equal digestible protein and energy basis. The experimental period was 140 days and fish weights and feed intakes were measured at 28 day intervals. At the end of the experiment, liver and fillet samples were collected from fish for the measurement of hepato-somatic indices and fillet composition, respectively. Fish fed the FO/FM100 or VO/FM100 diets had the highest weight gain over the 140 day experimental period (257.3 and 271.4 g); thus the replacement of fish oil with a mixture of canola and linseed oil did not adversely affect fish growth. However fish fed the VO/FM 50, VO/FM25 or VO/FM0 diets had significantly (P < 0.05) lower weight gain (228.3 and 202.2 g) than fish fed the VO/FM100 diet. Replacement of fish meal and fish oil with canola protein concentrate and canola:linseed oil mixture resulted in significant (P < 0.05) reduction of residual concentration of PCDD/F and DL-PCBs in fish diets and fillets but also reduced the level of 20:5n-3 and 22:6n-3 in the fish fillets. Replacement of fish oil and meal with vegetable oils and proteins can reduce the level of PCDD/F and DL-PCBs in farmed fish.