Effects of dietary fish oil replacement by blending vegetable oils on fattening performance, physiological metabolism indices and biochemical composition of adult female Portunus trituberculatus

In order to investigate the effects of dietary fish oil replacement with blending vegtable oils on the fattening performance, physiological metabolism and biochemical composition of adult female swimming crab (Portunus trituberculatus), five isonitrogenous and islipidic fattening diets were formulated to replace 0%, 25%, 50%, 75% and 100% of fish oil (defined as Diet 1-Diet 5) with blending vegtable oils (soybean oil∶rapeseed oil=1∶1). The five fattening diets were fed to female P. trituberculatus (150±25) g for 45 days. The results showed as follows: ① Dietary fish oil levels had no significant effects on survival rate, weight gain rate, gonadosomatic index and hepatosomatic index, meat yield and total edible yeild of adult female P. trituberculatus. ②There were significant differences in the triglyceride (TG) content, malate dehydrogenase (MDH) lipase (LPS) and lipoprotein lipase (LPL) activities in the hepatopancreas among five diet treatments; the highest levels of TG and LPS were detected in Diet 5, and the highest MDH was detected in Diet 1, while the highest LPL was detected in Diet 2. The highest TG and TC were detected in Diet 3 and Diet 4, respectively. ③ The hepatopancreatic peroxidase (POD) activity of the crabs in Diet 1 was significantly higher than that of Diet 2 and Diet 3, while the Diet 4 had the highest activities of hepatopancreatic alkaline phosphatase (ALP) and acid phosphatase (ACP). The highest and lowest values of total superoxide dismutase (T-SOD) activity in the serum were detected at treatments of Diet 2 and Diet 1, respectively, while the highest serum ALP activity was detected in Diet 1. ④ Dietary fish oil replacement has significant effects on the contents of crude protein and total carbohydrate in muscle, and the highest levels of crude protein and total carbohydrate in the muscle were dected in Diet 3. There were significant differences in the contents of total lipid and total carbohydrate in the hepatopancreas among five treatments, and the higher levels of them were detected for Diet 3 and 4 treatments; moreover, the highest ovarian crude protein content was also detected in Diet 3 treatment. ⑤ Dietary fish oil replacement had significant effects on the fatty acid profile of muscle, ovary, and hepatopancreas; tissue n-6 polyunsaturated fatty acid (n-6 PUFA) increased with increasing dietary fish oil replacement level, while the contents of n-3 PUFAs and highly unsaturated fatty acid (HUFA) showed a decreasing trend. In conclusion, dietary fish oil replacement by vegetable oils had no siginificant effect on survival rate and fattening performance of adult female P. trituberculatus, but promote the TG, crude lipid and n-6 PUFA accumulations in the hepatopancreas as well as the POD and phosphatase; 50% fish oil replacement level could increase the crude protein conetent of ovaries and muscle. These results indicated the dietary optimal fish oil replacement with blending vegetable oils could be 50% for the fattening of adult female P. trituberculatus.