REPLACING FISH MEAL WITH RAPESEED MEAL ON GROWTH PERFORMANCE, ANTIOXIDANT CAPACITY AND DIGESTIVE SYSTEM MORPHOLOGY OF JUVENILE PROCAMBARUS CLARKII

To elucidate the effects of rapeseed meal replacing fish meal on growth performance, feed utilization, digestive activity and antioxidant capacity of juvenile Procambarus clarkii, five isonitrogenous and isocaloric diets were formulated to feed juvenile Procambarus clarkii with the average initial body weight of (2.49±0.01) g for 42d. The inclusion levels of rapeseed meal were 0, 21.25%, 42.50%, 63.75% and 85% by using rapeseed meal instead of fish meal in different proportions 0 (R0), 25% (R25), 50% (R0), 75% (R0) and 100% (R0), respectively. The results showed that: (1) no significant differences in FBW, SGR, FE, and PER were observed among the R0, R25 and R50 groups (P>0.05), however, FBW, SGR, FE, and PER in R75 and R100 groups were significantly lower than those in R0 group (P<0.05). Compared with the R0 group, the crude protein and crude lipid contents of juvenile Procambarus clarkii in the R50, R75 and R100 groups were significantly reduced (P<0.05). The activities of hepatopancreatic trypsin, hepatopancreatic lipase and intestinal trypsin of juvenile Procambarus clarkii in the R75 and R100 groups were significantly lower than those in the R0 group (P<0.05), while there was no significant difference in amylase activity among all the groups (P>0.05). NPY and TRY genes expressions levels in hepatopancreas and intestine of R75 and R100 groups significantly decreased than those of R0 group (P<0.05), while MSNP gene expression level significantly increased (P<0.05). (2) Hepatopancreatic alkaline phosphatase (AKP), alanine aminotransferase (GPT), and aspartate aminotransferase (GOT) activities in the R100 group significantly increased compared with the R0 group (P<0.05). With the increase of rapeseed meal level, the activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione S-transferase (GST) in hepatopancreas showed a decreasing tendency, which in the R75 and R100 groups were significantly lower than those in the R0 group (P<0.05). The expression levels of AKP gene in hepatopancreas and intestine of the R50, R75 and R100 groups significantly increased compared with the R0 group (P<0.05), while the expression levels of CAT, SOD and GPX genes significantly decreased (P<0.05). (3) The structures of hepatopancreas and intestine in the R25 group were not significantly different from those in the R0 group. With the increase of replacement ratio, the vacuolation of hepatopancreas epithelial cells in the juvenile Procambarus clarkii gradually increased, R cells atrophy by degrees, and the hepatopancreas tubules lumens were misshapened and had become enlarged. The intestinal cells fall off and the intestinal villi become significantly shorter. In summary, the appropriate content of rapeseed meal in the feed for juvenile Procambarus clarkii should not be more than 21.25%.