Effect of growth rate on quality traits and feed utilisation of rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis)

Rainbow trout (Oncorhynchns mykiss) of initial average weight 150 g and brook trout (Salvelinus fontinalis) initially weighing 124 g on average, were reared at different growth rates by feeding either a high (H, close to satiation) or low (L, half of H) ration of a commercial diet. Fish were reared for 6 to 15 weeks in order to reach same size class. Fast growth increased whole body lipid and dry matter (P < 0.01) but reduced ash in both species (P < 0.01). Brook trout were both more fat and had higher protein content, lower moisture and lower ash content than the rainbow trout (P < 0.01). Neither the feed conversion ratio (FCR = g feed intake g weight increase(-1)) nor protein retention efficiency (PRE) was affected by growth rate. The brook trout, however, were more efficient in retaining protein than the rainbow trout (P < 0.01). Enhanced growth increased fat content in fillets (P < 0.01). Like in whole body protein and dry matter was higher (P < 0.01) in brook trout fillets than in fillets from rainbow trout. Carcass percentage was in overall lower (P < 0.01) at high growth rates compared to slow growth while both carcass percentage (P < 0.01) and fillet yield (P < 0.01) was lower in brook trout than in rainbow trout. (C) 2000 Elsevier Science B.V. All rights reserved.