Study On The Diversity Of Bacterial Community In The Intestine Of The Large Yellow Croaker(Larimichthys Crocea)

The large yellow croaker is an important economic marine fish,which has the highest production and maximum area of cage culture in China.Previous study found that intestinal bacterial community can stimulate epithelial cell proliferation and promote nutrient metabolism and innate immunity in fish.Studying the intestinal bacterial community can facilitate the selection of probiotics,prebiotics and chemical compounds with potentials to improve the gut homoeostasis of fish.The large yellow croaker is an important economic marine fish.And it is of great significance to study the intestinal bacterial-community of the large yellow croaker.In this study,the large yellow croaker was chosen as the research object,we used Illumina high throughput sequencing platform to carry out the sequences in V4 region of 16S rRNA gene of the bacterial community in the intestine.We analyzed the diversity of the intestinal bacterial community of the large yellow croaker in different cultural environment and stages,as well as were fed with artificial feed.The main findings are as follows:(1)In order to study the diversity of bacterial community in different digestive organs of large yellow croaker,the gastric caecum,pyloric stomach,pyloric caecum,rectum,small intestine and other digestive organs of eight large yellow croakers in the same cage were collected and analyzed.The principal co-ordinates analysis(PCoA)based on weighted Unifrac distance showed that there was obvious difference between the bacterial communities in small intestine and other organs.Analysis of molecular variance(Amova)indicated that there was extremely significant difference between the bacterial communities in small intestine and gastric cecum.(2)In order to study the difference of intestinal bacterial community in different culture environments,as well as the core bacterial community of large yellow croaker,four groups large yellow croaker cultured in cages in Ningde area and two groups wild large yellow croaker near Min jiang Estuary and Nao zhou Island individually were analyzed.Analysis of molecular variance and principal co-ordinates analysis were used to evaluate the diversity of bacterial community.The results showed that there were significant difference among the group near Nao zhou Island and all cage cultured groups(Amova,P<0.001).The results of alpha diversity analysis showed that shannon index increased with the increase of body weight and the chao index in Min jiang Estuary group was highest.In addition,Alphaproteobacteria,Betaproteobacteria,Gammaproteobacteria,Clostridia and Bacteroides were the main dominant bacterial classes.The occurrence probability of 12 kinds of bacteria in the intestine of each group was more than 60%,we believed these bacteria were the core bacteria of large yellow croaker.(3)In order to study the effect of artificial diet on intestinal bacterial community of large yellow croaker,we treated the large yellow croakers fed surimi with starvation for 3 days,and then fed with artificial diet.The guts were sampled after two and four weeks independently.The results of alpha diversity analysis showed that there was extremely significant decrease between the the bacterial communities of cage cultured fish and the fish fed artificial diet 2 weeks,and there was significant decrease between the the bacterial communities of cage cultured fish and the fish fed artificial diet 4 weeks.Rank sum test results indicated that the relative abundance of 11 bacteria were significantly different between the fish fed surimi and artificial diet.(Mann-Whiteny U,P<0.01).(4)In order to study the changes of intestinal bacterial community during early development of large yellow croaker,two groups fish in two different ponds were selected and analyzed.The first group included juveniles on the 13th,20th,25th and 30th day after hatching,and the second group included juveniles on the 12th,18th and 20th day after hatching.Copepods were predominantly consumed from 12 to 20 days after hatching,and artificial diet was predominantly consumed from 20 to 30 days after hatching by large yellow croaker.The results of alpha diversity showed that shannon index increased with time from the 13th day to the 25th day after hatching in first group,and decreased after 30th day after hatching.The results may be due to the change of the feed.And the shannon index increased with time from the 12th day to the 20th day after hatching in second group.Some bacteria,such as Photobacterium,Haemophilus and Streptococcus,were found to be relatively abundant in the intestines of fish at each time point,and these bacteria were also detected in cage cultured fish.Through this study,we found that culture environment and artificial feed can affect the intestinal bacterial community of large yellow croaker.The diversity of intestinal bacterial community at different developmental stages is different.And revealed the core bacterial community of large yellow croaker.These results provided new strategies for manipulating GI microbial communities to promote fish health and developing feed.