EFFECTS OF DIETARY LIPID LEVEL ON GROWTH AND LIPOPROTEIN LIPASE GENE EXPRESSION IN PELTEOBAGRUS VACHELLI

Dietary lipid plays an important role in commercial diet as a source of energy and essential fatty acids for the growth and development of fish.Darkbarbel catfish (Pelteobagrus vachelli) is an important freshwater aquaculture species in China.Due to its high market value,the culture of this specie has increased rapidly in recent years.Lipoprotein lipase (LPL) is considered as a key enzyme in the lipid deposition and metabolism.LPL hydrolyzes triglycerides present in plasma lipoproteins and supplies free fatty acids for storage in adipose tissue,or for oxidation in other tissues.Information on LPL gene expression and its regulation in fish remains very scarce.The present study was conducted to investigate the effect of dietary lipid level in early juvenile of darkbarbel catfish (Pelteobagrus vachelli) with regards to survival,growth,fish body composition and liver LPL gene expression.Five isonitrogenous diets containing 4.7%,7.9%,10.9%,15.4% and 18.9% lipid were formulated respectively.Each diet was randomly assigned to triplicate groups of tanks,and each tank was stocked with 100 fish (21 days after hatchery,with initial average weight 71±5mg).Fish were fed to satiation three times daily for 30 days.During the experimental period,the water temperature fluctuated from 21℃ to 25℃.The results showed that dietary lipid significantly affected the growth of darkbarbel catfish (P<0.05).Specific growth rates (SGR) of darkbarbel catfish increased with the increase of dietary lipid level from 4.7% to 10.9%,and then showed a threshold.Dietary lipid level significantly affected fish body proximate composition (P<0.05).Dry matter and lipid content of whole body significantly increased with increasing dietary lipid level (P<0.05) while protein content of whole body significantly declined with increasing dietary lipid level (P<0.05).Liver lipoprotein lipase (LPL) gene of darkbarbel catfish was cloned.The length of cloned LPL cDNA sequence (GenBank accession number:EU882966) was 528 bp.Homologous alignment analysis showed darkbarbel catfish LPL gene had 81% homology to that of zebrafish.At the end of growth trial,darkbarbel catfish liver LPL mRNA level was examined by real time PCR.High lipid diet drastically stimulated liver LPL gene expression in darkbarbel catfish.Fish fed with 15.4% and 18.9% dietary lipid had significantly higher LPL mRNA level in liver (P<0.05).Broken-line analysis based on SGR indicated that the optimal dietary lipid level for the early juvenile of darkbarbel catfish was 11.2%.