| Chinese mitten crab (Eriocheir sinensis) is called river crab, is belong to crustaceaclass, decapoda order, square crab family, and mitten crab genus, is a specialty in China,It mainly lives the coast of Chinese eastern sea and the rivers, lakes connected with sea,now is a main aquaculture economic crabs species in China. In2011, annualaquaculture production reached about600,000metric tons. Highly unsaturated fattyacids (HUFA) mainly included arachidonic acid (ARA,20:4n-6), eicosapentaenoic acid(EPA,20:5n-3) and docosahexaenoic acid (DHA,22:6n-3). HUFA has an importantregulatory role on the growth, molting, gonad development, immune protection and theresistance to environmental stress. The researchs about the nutritional requirementsHUFA in crabs are absence, this is very detrimental to the healthy development of rivercrab breeding, so studying the relationship of dietary HUFA nutritions and the growthperformance of juvenile crab is meaningful in theory and reality. The juveniles bothmale and female individuals existed different growth characteristics, So the HUFAdemand may also existed particular differences. Therefore, the gender difference shouldbe considered into the discussing of the HUFA nutritional requirements in juveniles. Forthat reason, the effects of dietary DHA levels and DHA/EPA ratios on survival, molt,growth and lipid composition of juvenile Chinese mitten crab Eriocheir Sinensis(theinitial body weight is about0.6g and0.4g, respectively), by precisely regulating theDHA levels and DHA/EPA ratios of the purified diets, under the condition of singleindividual breeding were studied in the experiments. Then the appropriate content ofDHA and DHA/EPA ratio in the diets of male and female individuals were researched.1. The effects of dietary DHA content on the growth and lipid composition of juvenileChinese mitten crab Eriocheir SinensisDocosahexaenoic (DHA,22:6n-3) has an important regulatory role on the growth,molting, gonad development, immune protection and the resistance to environmental stress of the crustacea. Studying the relationship of dietary fatty acids nutritions, thegrowth performance of juvenile crab and the resistance to hypoxia stress is meaningfulin theory and reality. The effects of dietary DHA levels on survival, growth and lipidcomposition of juvenile Chinese mitten crab Eriocheir Sinensis(the initial body weightis about0.6g) by single individual breeding and biochemical analysis methods etc. werestudied in the experiment, then the appropriate DHA content in the diets of juvenile crabwere investigated eventually. The results showed that,(1)Hepatopancreas index (HSI)of female crab in the D4group was significantly lower than the other four groups (P <0.05), DHA content had no significant impact on the HSI of male crab of five groups.With the increase of dietary DHA content, the first molting interval of female crab in allgroups had a tendency to markedly shorten (P <0.05), but the second molting intervalhad a extending tendency; both the first and second moilting intervals for the male crabhad the shortening tendency. From the overall, weight gain rate of male crab wasgenerally higher than that of female crab, the final carapace length of male crab waslonger than that of female crab, the mean first molting interval of the juveniles wasshorter than the mean second molting interval.(2)Total lipid content of thehepatopancreas for the female crab of D4group was significantly lower than the otherfour groups (P <0.05), total lipid content of the hepatopancreas for the male crab of fivegroups increased dramatically (P <0.05). On the whole, with the increase of the dietaryDHA content, total lipid content of the hepatopancreas for the juveniles had a graduallyrising trend;(3)DHA content in the hepatopancreas and muscle for juvenile crabsincreased significantly with the increase of the dietary DHA content, but the relativeretention rate of DHA decreased significantly accordingly, PUFA relative retention ratein muscle were much higher than that in hepatopancreas. No matter how the dietaryDHA/EPA changed, the DHA/EPA in muscle was always less than1, this indicated thatthe muscle of juvenile crab needed more EPA; In conclusion, the appropriate DHAcontent of the diets for the juvenile crab was approximately0.2%.2. The effects of dietary DHA/EPA on the growth and lipid composition of juvenileChinese mitten crab Eriocheir SinensisThe effects of dietary DHA/EPA on the survival, molt, growth and lipidcomposition of juvenile Chinese mitten crab Eriocheir Sinensis(the initial body weightis about0.4g) by single individual breeding and biochemical analysis methods etc. werestudied in this experiment, then the appropriate DHA/EPA in the diets of juvenile crab were investigated eventually. The results showed that,(1)The dietary DHA/EPA had nosignificant influence on the survival, molting and HSI of the juveniles, but the wholesurvival rate of the male was generally higher than that of the female;(2) Growth speedof female crabs when the dietary DHA/EPA was1was slower than the other groups; themale crabs when the dietary DHA/EPA was3grew fastest in the experiment.(3)Whenthe dietary DHA/EPA was higher than the juvenile crab’s need, the total lipid content inhepatopancreas increased significantly (P <0.05);(4) The relative retention rate of DHAin the muscles of the crabs decreased and the relative retention rate of EPA significantlyenhanced with the increase of the dietary DHA/EPA;(5)With the increase of the dietaryDHA/EPA, DHA, DHA/EPA and ARA/EPA in the hepatopancreas and musle markedlyimproved, while the EPA content markedly decreased.(6)Contents of ARA, EPA andDHA in the muscle were much higher than that in the hepatopancreas and diets, thissuggested that the muscle required high content of HUFA to maintain its physiologicalfunctions. In conclusion, the suitable proportion of the dietary DHA/EPA was2-3,which the growth performance and lipid composition both were taken into account.From the above, the appropriate addition of DHA and DHA/EPA to the diets hadsignificant promoted effect on the growth of juvenile crabs, the growth speed betweenmale and female individuals had certain differences, currently male crabs grew fasterthan female crabs. The appropriate DHA content of the diets for the juvenile crabs wasapproximately0.2%, the suitable proportion of the dietary DHA/EPA was2-3. |
