Effects of replacing dietary fish oil with canola oil on immune factors and enzymes of rainbow trout (Oncorhynchus mykiss)

Replacing dietary fish oil with vegetable oils has various effects on immune responses. This study was conducted to evaluate the effect of replacement of fish oil (FO) by canola oil (CO) on immune system of the rainbow trout Oncorhynchus mykiss (63.5±0.6 g mean individual weight) for 50 days. Four experimental diets were formulated with partial or complete (33%, 67%, 100%) replacement of FO with CO. The diets were fed to duplicate groups of 25 trout fingerlings. Fish were randomly assigned to each of eight 500 liter fiberglass tanks (500L). The results showed that serum AST, ALP, ALT and LDH levels were higher in fish fed the 100% FO diet than the other fish. Serum lysozyme activity and immunoglobulin (IgM) was higher in fish fed the 100% FO diet than the other fish. Also, 3 and C4 complements were significantly higher in fish fed the 100% FO diet than that the other fish. However, alternative complement activity (ACH50) was higher in fish fed the 100% CO diet. Since the amounts of serum liver enzymes in CO treatment groups was lower than their amounts in FO treatment group, so we can conclude that replacing dietary FO with CO does not have any negative effects but it causes improvement of immune factors and enzymes of rainbow trout (Oncorhynchus mykiss) in period of 50 days.