Effects of stocking density on the growth performance，intestinal digestive enzyme activities and microflora structure of Litopenaeus vannamei

【Objective】To investigate the effects of stocking density on the growth performance，intestinal digestive enzyme activity and intestinal microflora structure of Litopenaeus vannamei. It could provide theoretical reference for the reasonable setting of medium density in L. vannamei aquaculture.【Method】Three stocking densities（100，200 and 300 tails/m3）were set up. L. vannamei with an initial body weight of 0.30±0.02 g were fed using the same feed in the same size fiberglass drums（0.3 m3）for 8 weeks. At the end of the experiment，the growth performance，intestinal digestive enzyme activity and intestinal microflora were analyzed. Three replicates were set upfor each treatment group.【Result】The increase of stocking density significantly reduced the final mean weight，weight gain and specific growth rate（P<0.05，the same below），but significantly increased the feed coefficient and digestive enzyme activities includingtrypsin，lipase and amylase of L. vannamei. The alpha indexes in the intestinal microflora of L. vannamei decreased with the increase of culture density. The observed_species（Sobs），Chao1 and Shannon indexes were significantly different between low and high density groups，and significant differences in ACE and Pielou indexes among low，medium and high density groups were found. The change of culture density significantly affected the intestinal microflora structure of L. vannamei. At the phylum level，the abundance of Proteobacteria significantly increased，while the abundance of Verrucomicrobia，Plantomycetes，Actionobacteria，Patencibacteria and the ratio of Firmicutes to Bacteroides significantly decreased. At the family level， the abundance of Vibrionaceae，Flavobacteriaceae，Erysipelotrichaceae and Psychromonadaceae significantly increased， while the abundance of Rhodobacteraceae and Moraxellaceae significantly decreased. At the genus level，the abundance of Vibrio，Acinetobacter and Spongiomonas increased significantly，while the abundance of Motilimonas，Ruegeria and Planctomicrobium decreased significantly. Tax4fun function prediction showed that the functional abundance related to carbohydrate metabolism，membrane transport，amino acid metabolism，signal transmission，metabolism of cofactors and vitamins，and energy metabolism were high among the 36 predicted functions. BugBase phenotype prediction showed that the increase of stocking density significantly reduced the phenotypic abundance of biofilm forming related to gram negative bacteria，but significantly increased the phenotypic abundance of gram positive bacteria.【Conclusion】Highstocking densities will reduce the growth performance，stimulate the secretion of intestinal digestive enzymes，and significantly change the structure of intestinal microflora of L. vannamei.