Growth, physiological and immunological responses of rainbow trout (Oncorhynchus mykiss) to different dietary inclusion levels of dehulled lupin (Lupinus angustifolius)

The utilization of dehulled lupin as a partial replacement for fish meal was studied in diets of rainbow trout. Fish were fed diets with 0%, 10%, 20%, 30%, 40% and 50% of dehulled lupin, at a daily feeding rate of 2% body weight for 8 weeks at 15 +/- 0.5 degreesC. Growth performance generally decreased with increasing dehulled lupin in the diet (R-2 = 0.81, P < 0.0001). However, there was no significant difference between 0%, 10%, 20%, 30% and 40% dehulled lupin fed groups. Feed conversion ratio generally increased at higher inclusion levels of dehulled lupin (R-2 = 0.74, P < 0.002). The protein efficiency ratio, protein productive value, lipid efficiency ratio and lipid productive value were similar in all groups but the energy efficiency ratio was significantly lower (P < 0.01) in the 50% dehulled lupin fed group. Different treatments showed similar digestive enzyme activity, villus height, pyloric caeca and hepato somatic indexes, None of the nonspecific immune responses, with the exception of total plasma protein and neutrophils, was affected by different inclusion level of lupin. Results show that dehulled lupin can be included at up to 40% of a rainbow trout diet without a significant effect on growth performance or nutrient utilization, Rainbow trout utilize dehulled lupin protein as efficiently as fish meal protein but have a lower ability to utilize the energy content of dehulled lupin at higher inclusion levels.