No abstract

Frozen copepods, frozen adult Artemia, live rotifers and live Artemia nauplii were used as feed for the megalopa of Eriocheir sinensis during desalination stage to determine the most nutritious and cost‐effective feed. The biochemical composition of the four feeds was analysed. Then, the individual wet weight, individual dry weight, survival rate, the cost and the biochemical composition of the megalopa were measured after the desalination. The resulting effects on the metamorphosis ratio and the duration of the megalopa were also assessed. The results showed that the duration of desalinated megalopa to first stage crab for all treatments was approximately 3.5 days, while the metamorphosis rate of the copepod treatment was significantly higher than the other treatments with the value of 96.33 ± 3.79%. In terms of biochemical composition, after desalinization, the moisture content of megalopa in the adult Artemia treatment was the highest, and the total lipid in the Artemia nauplii treatment and rotifer treatment was significantly higher than the other two treatments. The desalinated megalopa from copepod treatment had the highest percentages of DHA (22:6n‐3) and EPA (20:5n‐3) among the four treatments. The desalinated megalopa from copepod treatment and rotifer treatment had the higher contents of protein. In conclusion, frozen copepods have higher nutritional value for the megalopa during the desalination period. Therefore, feeding the megalopa with copepods can improve the culture performance and megalopa quality, and can also reduce the feed cost during desalination stage.

A 120‐day trial was conducted to assess the effects of dietary fish oil replacement with vegetable oils on growth, lipid metabolism and antioxidant capacity of subadult swimming crab Portunus trituberculatus. Five isonitrogenous and isolipidic diets were formulated to replace 0, 250, 500, 750 and 1000g/kg of fish oil with a mixture of soybean and rapeseed oil (defined as D1–D5), and each treatment had 30 replicate crabs. Dietary fish oil replacement had no significant effects on growth of the crabs, while the D3 had the highest hepatosomatic index and total lipids in hepatopancreas. The triglyceride and lipase activities in hepatopancreas increased significantly with increasing dietary fish oil replacement. The D4 had the highest levels of alkaline phosphatase (ALP) and acid phosphatase (ACP) in the hepatopancreas, as well as the haemolymph ALP, ACP and peroxidase. The highest levels of haemolymph total antioxidant capacity, catalase and malondialdehyde were detected in D1. Total n‐3 polyunsaturated fatty acids levels in hepatopancreas decreased significantly with increasing dietary fish oil replacement. In conclusion, dietary fish oil replacement had no significant effects on growth of P. trituberculatus, and 500g/kg of fish oil replacement could improve antioxidant capacity, but excessive replacement level will enhance lipid accumulation and peroxidation in the hepatopancreas.