Effects Of Culture Density On Growth Of Juvenile Takifugu Rubripes In Recirculating Aquaculture System

Takifugu rubripes has an important influence in the world.Not only its meat is delicious,but also tetrodotoxin has high medical value.Therefore,it is very important to increase the yield of Takifugu rubripes,study the effect of culture density on the growth and development of Takifugu rubripes,and screen a reasonable range of culture density for it.In this paper,the Takifugu rubripes was used as the research object,and the culture experiment was carried out in three density groups:low density group(SD1 group,5kg/m~3),medium density group(SD2 group,7.5kg/m~3)and high density group(SD3 group,10kg/m~3).The growth performance index,antioxidant capacity,immune organ function and the changes of liver and spleen transcripts of Takifugu rubripes under different culture densities were studied and analyzed.The following conclusions are as follows:1.Density stress has an important effect on the daily behavior and growth performance of Takifugu rubripes,and this effect may be strengthened with the increase of culture time.At the end of the experiment,the body weight(283.36g)and survival rate(87.84%)of Takifugu rubripes in SD1 group were significantly higher than those of SD2 and SD3(232.37g,203.01g)and survival rate(82.32%78.09%)(P<0.05).2.Density stress has significant effects on physiological and biochemical indexes of juvenile Takifugu rubripes.In terms of key indexes,SOD index in SD1 group was significantly higher than that in SD2 and SD3 groups(P<0.05),CAT was slightly lower than that in SD2group but significantly higher than that in SD3 group(P<0.05),GPX was slightly lower than that in SD2 group but significantly lower than that in SD3 group(P<0.05),MDA was significantly lower than that in SD2 and SD3 groups.There was no significant difference between ALT and SD2 and SD3 groups(P>0.05),while there was no significant difference between AST,AKP and T-AOC(P>0.05).The results on 90 days were opposite to those on 30 days,and some maintained the same trend.3.Density stress also had significant effects on transcriptome analysis of liver and spleen of juvenile Takifugu rubripes.In this study,differential gene analysis,GO enrichment analysis and KEGG enrichment analysis were used to analyze and judge the sequencing results.From the results of the above three analysis methods,Some common differential genes were identified,such as C-C motif ligand 19(ccl19),bisspecific phosphatase 1(dusp1),pepsin D(Ctsd),glutamic oxaloacetic aminotransferase 1(got1),matrix metalloproteinase 7(adamts7),LOC101075981,type IV collagen col4 a1 and col4a2,integrin protein itag1 and itag4,which are related to immune system,stress response,growth and development,were significantly up-regulated or down-regulated during the whole experiment(P<0.05).To sum up,the effects of density stress on juvenile Takifugu rubripes fish may include oxidative damage to the liver,delayed growth and development,increased mortality,decreased energy metabolism,immune and stress reactions and so on.Therefore,combined with the production practice,the author thinks that the optimum culture density range of juvenile Takifugu rubripes is 5kg/m~3～7.5kg/m~3.