Studies About Liquids Requirement Of Early Juvenile(C1) Swimming Crab Portunus Trituberculatus

Lipids are one of the main energy sources required by aquaculture organisms and are also the main components of the cell membrane.Because larvae and juveniles have limited lipid synthesis capacity,it must be provided by the feed.The lack of essential lipids can result in poor growth,increase mortality,abnormal pigmentation,immunodeficiency,skeletal deformities.As a bioactive substance,phospholipids have certain nutritional value and physiological functions,which has high application value.It has been studied that the lipids nutritional requirements of shrimp and crab from aspects of physiological functions and metabolism.Although some studies have been conducted on the lipid nutrition of Portunus trituberculatus juvenile,there is a lack of understanding of the requirement and mechanisms of Portunus trituberculatus larvae.In order to increase the survival rate of Portunus trituberculatus larvae,it is necessary to study its requirement for the main lipids.In this paper,we studied the effects of different dietary phospholipids and lipid levels on the growth performance,survival,molting,gene expression,digestive enzyme activity and fatty acid composition.The main contents include the following aspects:(1)A 30-day experiment was conducted to investigate the effect of phospholipids(PLs)on growth performance,survival,fatty acid profile and gene expression of the early juvenile(C1)swimming crab(Portunus trituberculatus).Five semi-purified diets were formulated with graded PLs levels(0 %,1%,2%,4% and 8%).Each diet was fed to 4 replicates of crabs(30 crabs replicate-1,initial weight: 8.4 ± 0.1 mg).In this study,crabs fed diets with 0% and 1% PLs had significant lower weight gain than crabs fed with 8% PLs.But crabs fed with diets containing 2%,4% and 8% PLs showed no significant difference in weight gain.The survival of the crabs ranged from 63.09 to 78.97%.And crabs fed diets with 2%,4% and 8% PLs had significantly higher survival rates than crabs fed with 0% and 1% PLs.Besides,the content of EPA and DHA in whole body was higher than that in diets,but the MUFA content showed an opposite trend.The EPA and DHA content in whole body increased with the increase of dietary PLs.Moreover,the molting number increased with the increasing dietary PLs levels,the lowest molting number was observed in crabs fed diets without supplementation of PLs.The EcR was found to be significantly up-regulated by PLs levels.This study demonstrated that 2% PLs could meet the requirement of early juvenile(C1)swimming crab based on the growth and survival.And 4-8% PLs supplemented in diets could reduce the leaching of feed.(2)The main objective of this investigation was to study the lipid requirements of the early juvenile(C1)swimming crab(Portunus trituberculatus)based on growth performance,survival,molting and fatty acid profile.Four test diets were formulated with graded lipid levels(3.63%,6.70%,10.72% and 13.91%).Each diet was fed to 4 replicates of crabs(30 crabs replicate-1 initial weight: 8.4 ± 0.1 mg).In this study,crabs fed diets with 13.91% lipid had significantly(P < 0.05)higher survival than crabs fed with 3.63% lipid,but no significant(P > 0.05)improvement of survival was observed when dietary lipid increase from 6.70 to 13.91%.Crabs fed diets with 10.72% and 13.91% lipid had significant higher WG than crabs fed with 3.63% lipid.But crabs fed with diets containing 6.70%,10.72% and 13.91% lipid showed no significant(P > 0.05)difference in WG.Moreover,the lowest molting number was observed in crabs fed diets with 3.63% lipid,but there was no significant difference(P > 0.05)among other groups.The content of LC-PUFA and DHA in the crabs fed diets with 3.63% lipid was significant(P < 0.05)lower compared to other groups.But there was no significant(P > 0.05)difference in EPA and ARA content among all groups.The activity of lipase increased as dietary lipid level increased(from 6.70 to 10.72%).However,beyond 10.72%,a significant(P < 0.05)decreased in lipase activity was observed.The regression analysis of weight gain data indicated that crab fed diet containing 10.47% lipid level is considered as optimum lipid level for its maximum growth and molting process.