Effects Of Dietary Phospholips On Growth Performance And Phospholipids Metabolism Of Larval And Juvenile Large Yellow Croaker (Larmichthys Crocea)

This study was conducted to investigate the effects of dietary phospholipids ongrowth of larval and juvenile large yellow croaker (Larmichthys crocea). On basis ofthe above studies, the further study was aimed to investigate the mechanism ofphosphatidylcholine synthesis in large yellow croaker. The results and conclusions aresummarized as follows1. Effects of dietary phospholipids on growth and body composition of larvaland juvenile llarge yellow croaker (Larmichthys crocea）The study was conducted to investigate effects of dietary phospholipids on growthand body composition of larval and juvenile large yellow croaker (Larmichthyscrocea). Three isoproteic and isolipidic diets were formulated with graded levels ofphospholipids (0%,5%and12%) for larvae. The diets and live copepod wererandomly allocated to triplicate groups of larvae (initial body weight3.86±0.24mg)eight times daily for30days. Five isoproteic and isolipidic diets were formulated withgraded levels of PLs (0%,2%,4%,6%and8%) for the juvenile. The juvenile (initialaverage weigt7.36±0.33g) were fed twice daily to apparent satiation for60days.Results showed that with the increase of dietary phospholipids, survival rate, specialgrowth rate (SGR) and body length of larval large yellow croaker increased. Thesurvival rate, SGR and body length of fish larvae fed phospholipids-devoid diet weresignificantly lower than fish larvae fed live prey and phospholipids-supplementeddiets (P<0.05). No significant difference was found betweenphospholipids-supplemented group and control group (P>0.05). However, dietaryphospholipids did not significantly affect the survival rate and SGR of juvenile large yellow croaker (P>0.05). The body lipid content of fish larvae had the same variationwith SGR. In larval stage, with the increase of dietary phospholipids, whole bodylipid content decresed first and then increased. The whole body lipid content waslowest in fish fed diet with5.86%PL and significantly lower than other groups(P<0.05). The lipid content in liver increased first and then decreased with theincrease of dietary PL. When dietary PL was3.05%, lipid content in liver was thehighest and significantly higher than other groups (P<0.05). Liver lipid content in lowPL level (1.32%) was significantly higher compared with higher PL level (7.4%and9.63%), but no significance was found compared to moderate phospholipids level(5.86%). In conclusion, the beneficial effects of dietary PLs on growth in Larmichthyscroacea were restricted to the start-feeding fry stage and dietary PL failed to affect thegrowth of juvenile large yellow croaker. However, moderate phospholipids mayenhance the asorption and transport of lipid in juvenile satge.2. Gene cloning and ontogeny of gene expression of phospholipids metabolismrelatedgenesIn the present study, the cDNA of CTP: phosphocholine cytidylyltransferase (CCT)and cytosolic phospholipase A2(cPLA2) from large yellow croaker (Larmichthyscrocea) was cloned by homology cloning with degenerate primer and RACEtechniques. CCT cDNA (GeneBank: KF006240.1) consists of2419bp in size with anopen-reading frame encoding369amino acid, a273bp5’-untranslated region and a1010bp3’-untranslated region. cPLA2cDNA (GeneBank: KF006240.1) consists of2169bp in size with an open-reading frame encoding723amino acid, a176bp5’-untranslated region and a205bp3’-untranslated region. Based on multi-sequencealignments and phylogenetic analysis, the CCT and cPLA2of large yellow croakershared ahigher degree of homology with other species of fish, but lower levelshomology between large yellow croaker and mammalian. As larval large yellowcroaker grew up, the present study detected the mRNA expression of CCT and cPLA2.Results showed that after hatchery as larval large yellow croaker grew up, theexpression of CCT and cPLA2significantly increased first and then significantlydecreased, maintained stable in the end. Regular changes of the expression of CCT and cPLA2could indicate the development of digestive system in larval large yellowcroaker.3. Effects of dietary phospholipids on the synthesis of phosphatidylcholine inlarval and juvenile large yellow croakerResults showed that the expression of phospholipids metabolism related genes suchas CCT, CPT, DGAT, PEMT and cPLA2were not significantly affected by dietary PLsin larval stage (P>0.05). As dietary phospholipids increased, the expression of sPLA2in larvae decreased. The expression of sPLA2in larvae fed phospholipids-devoid dietshowed maximum value and significantly higher than fish larvae fed live prey andphospholipids-supplemented diets (P<0.05). The expression of LPCAT in fish larvaefed live prey was significantly higher than larvae fed artificial diets (P<0.05). Duringjuvenile stage, the expression of CCT, CPT, DGAT, LPCAT, PEMT, cPLA2andsPLA2were not significantly affected by dietary PLs (P>0.05). In larvae stage, theexpression of MTP in fish larvae fed PL-devoid diet was significantly higher thanother two treatment groups and control group (P<0.05). However, dietary PLs did notsignificantly affect the expression of MTP in juvenile large yellow croaker (P>0.05).In conclusion, the regulation of phosphatidylcholine synthesis related genes mayoccur in protein level or phosphorylation level rather than transcriptional level. NewPC species from PC remolding may be critical for lipoprotein metabolism.