Effect and interaction of rainbow trout strain (Oncorhynchus mykiss) and diet type on growth and nutrient retention

Eight strains of rainbow trout were introgressed to develop a single strain (H-ARS) that was selected for faster growth when fed a fishmeal-free, plant-based diet (Selection Diet). For four generations, families from these crosses were fed the Selection Diet and selected for increased weight gain. Growth and nutrient retention were compared among H-ARS and two parental strains, the House Creek (HSC) and Fish Lake (FL) fed either a fish meal or Selection diet for 12weeks. There was a significant effect of strain (P<0.01), but not diet on weight gain, and a significant interaction of strain by diet (P<0.05). The H-ARS trout gained more weight averaged across diet (991% of initial wt.) than the HC (924%) or FL trout (483%). The FL trout fed the fish meal diet gained more weight than FL trout fed the selection diet (510% vs 456%). Conversely, H-ARS trout fed the plant-based diet gained more weight than those fed the fish meal diet (1009% vs 974%). HSC trout had similar weight gain fed either diet (922% vs 926%). A significant effect of strain on protein retention (P<0.01) was observed, along with a significant strain by diet interaction (P<0.02). The results demonstrate that rainbow trout can be selectively improved to grow on a plant-based diet.