1. Abstract:
A 6-week feeding trial was conducted to evaluate the effects of dietary canola protein
concentrate (CPC) on growth, gut and liver histology, brush border and metabolical enzymes,
intestinal microflora and organoleptic characteristics in rainbow trout (Oncorhynchus mykiss).
Twelve experimental tanks were stocked with 30 fish each. Fish received isonitrogenous and
isoenergetics experimental diets with 0, 30, 40 and 50% (designated as control/A, B, C and D)
inclusion of CPC. Fish were fed twice daily to satiation. The results showed that inclusion of 40%>
CPC has no negative impact on specific growth rate and daily growth coefficient. Plasma growth
hormone level was not affected by diet and did not change. Inclusion of CPC in the level of 50%
caused histological changes in mid gut as decreasing the number of goblet cells and absorptive
vacuoles and also caused abnormalities in brush border part of hindgut. Liver was not effected by
diet. Increasing the level of dietary CPC caused increment the activity of alkaline phosphatase,
leucine aminopeptidase and maltase. The concentration of alanine amino transferase and asparatate
amino transferase also affected by dietary protein source and level. Inclusion of CPC induced
changes in intestinal microflora and the population of lactic acid bacteria increased significantly
(P<0.05). The significantly (P<0.05) lower quality of tissue and taste obtained in the treatment of
D as compared to that of control treatment. Appearance of fish flash was affected by dietary protein
source and had significantly (P<0.05) better quality in control diet as compared to other treatments.