Abstract:This experiment was conducted to evaluate the effects of replacing soybean oil with rubber seed oil on growth performance, digestive enzyme activities, serum lipoprotein levels, protein metabolism indices and antioxidant capacities of grass carp (Ctenopharyngodon idellus). Five isoproteic and isolipidic experimental diets were formulated with rubber seed oil replacing 0%, 25%, 50%, 75%, and 100% of soybean oil (R0, R25, R50, R75, and R100), respectively. The results showed that the weight gain, daily gain coefficient in fish fed R0 and R50 diets were significantly higher than those in fish fed the R100 diet (P < 0.05). With increasing rubber seed oil replacement level, the feed coefficient first decreased and then increased, and the lowest value was observed in fish fed the R25 diet, which was significantly lower than that in fish fed the R50, R75, and R100 diets (P<0.05). Conversely, protein efficiency first increased and then decreased, and the highest value was observed in fish fed the R25 diet, which was significantly higher than that in fish fed other diets (P<0.05). With increasing rubber seed oil replacement level, intestinal trypsin and lipase (LPS) activity first increased and then decreased, and the highest values of intestinal LPS activity were observed in fish fed the R25 diet, which were significantly higher than that in fish fed other diets (P<0.05). The highest values of intestinal trypsin activity were observed in fish fed the R50 diet, which were significantly higher than that in fish fed R0, R75, and R100 diets (P<0.05). Hepatopancreas trypsin activity in fish fed R0 and R50 diets was significantly higher than that in fish fed R75 and R100 diets (P<0.05). The serum total cholesterol (TC) level in fish fed R25, R50, R75, and R100 diets were significantly lower than that in fish fed the R0 diet (P<0.05). With increasing rubber seed oil replacement level, hepatopancreas hepatic aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities first increased and then decreased, and the lowest value was observed in fish fed the R25 diet, which was significantly lower than that in fish fed R0 and R100 diets (P < 0.05). Further, plasma total antioxidant (TAC) capacity in fish fed R0 and R25 diets was significantly lower than that in fish fed R75 and R100 diets (P<0.05). Conversely, plasma and hepatopancreas malondialdehyde (MDA) levels in fish fed the R0 diet were significantly higher than in fish fed the R100 diet (P<0.05). These results indicated that replacing 25% to 50% of soybean oil with rubber seed meal had no obvious negative effects on growth performance, feed utilization rates, serum lipoprotein levels, protein metabolism indices, or antioxidant capacities, whereas replacing 50% of soybean oil with rubber seed oil may have depressed the growth performance and digestive enzyme activities of grass carp.
