Studies On N-3 Highly Unsaturated Fatty Acid Requirement Of Swimming Crab(Portunus Trituberculatus)

Feeding experiments were conducted to investigate the effects of dietary n-3 HUFA on survival, feed utilization and fatty acid composition of juvenile swimming crab(Portunus trituberculatus), one of wildly cultured as an important commercial carnivorous species in China. The content and results are summarized as follows: 1. Effects of dietary n-3 HUFA levels on growth performance, feed utilization and tissue fatty acid composition of juvenile swimming crabFour isonitrogenous and isoenergetic experimental diets were formulated to contain four n-3 HUFA levels(0.52%,1.12%,2.33% and 4.02%). White fishmeal and casein were used as protein sources. And DHA and EPA enriched oil were used for adjusting the n-3 HUFA levels. There were tiplicate(15 crabs per replicate) for each diet treatment. The crabs were fed(about 6-8% body weight) twice daily for 8 weeks. WG of swimming crab was significantly affected by dietary n-3 HUFA(p<0.05), WG of 2.33 group was significant higher than 0.52 and 4.02 group(p<0.05). As the incresaed of dietary n-3 HUFA levels, FCR declined and then increased. The lowest value appear in 2.33 group, and it was significant lower than 0.52 and 4.02 group(p<0.05). HSI decreased as the incresaed of dietary n-3 HUFA levels, and the value of 4.02 group was significant lower than 0.52 group(p<0.05).There was a positive correlation between tissue and dietary n-3 HUFA content. Based on growth proformance and feed utilization, the requirement for n-3 HUFA of juvenile swimming crab is about 2.33% of dry diet. 2. Effects of dietary DHA/EPA ratio on growth performance, feed utilization and fatty acid composition of juvenile swimming crabFour isonitrogenous and isoenergetic experimental diets were formulated to contain different DHA/EPA ratios(0.70, 0.84, 1.06 and 1.25). There were triplicate(15 crabs per replicate) for each diet treatment. The crabs were fed(about 6- 8% body weight) twice daily for 8 weeks. A good growth performance and feed utilization were observed in swimming crabs fed the diets with DHA/EPA ratio of 0.70 and 0.84, which had significantly higher weight gain(WG) and specific growth rate(SGR), compared with the crabs fed the diet with DHA/EPA ratio of 1.25(P<0.05). Survival of swimming crabs was increased as the ratio of DHA/EPA decreased. The DHA/EPA ratios in polar lipid from tissues were influenced by the DHA/EPA ratios in the diets. And the EPA/ARA ratios in hepatopancreas were lower than that in diets. Results of this study indicated that the growth performance and survival of juvenile swimming crab are correlated to the DHA/EPA ratio in the diets, and the best growth performance and survival were achieved with the ratio of 0.70-0.84.The results in this study indicated that growth and fatty acid composition of swimming crab was significantly affected by dietary DHA/EPA ratios and n-3 HUFA levels. The appropriate n-3 HUFA level was 2.33% of dry diet, and the appropriate DHA/EPA ratio was 0.70-0.84.