Effect Of Culture Density On Growth Performance Of Juvenile Siberian Hybrid Sturgeon

Sturgeon belongs to the class Osteichthys,the subclass Radiopterygium,the general order of cartilaginous hard scale,sturgeon form,is one of the oldest existing fish.Due to the sharp decline of wild sturgeon resources,the artificial sturgeon gradually dominates the market.At present,hybrid sturgeons are mainly cultivated,among which the Siberian hybrid sturgeon(Acipenser baerii♀×Acipenser schrenckii♂)is the most important species.This study to Siberia hybrid sturgeon larvae as the research object,set the low density group(LD,0.465 kg/m~2),medium density group(MD,0.694 kg/m~2)and high density group(HD,0.930 kg/m~2)for production test,the density of each set of three repeat group,the experiment cycle is 90 days,by the different density group growth parameters,body composition,antioxidant enzyme activity,muscle RNA-seq transcriptome and growth and stress related gene expression analysis,obtained the following results:The final weight,weight gain rate and specific growth rate of juvenile fish in LD group were significantly higher than those in MD and HD groups(P<0.05).There was significant difference in body weight at 30 days(P<0.05).There was significant difference in body length at 45d(P<0.05),and this difference lasted until the end of the experiment.There was no significant difference in survival rate among density groups.Water content and ash content increased with the increase of culture density,and there were significant differences(P<0.05).There were no significant differences in crude fat and crude protein,and there were no significant differences in fatness and hepatosomal index.(2)The effect of stocking density on liver antioxidant capacity of juvenile Siberian hybrid sturgeon mainly occurred in the later stage of culture experiment.The activity of superoxide dismutase(SOD)in medium density group was significantly lower than that in the other two groups at 75 d(P<0.05),and that in HD group at 90d was significantly lower than that in the other two groups(P<0.05).The activity of glutathione sulfur transferase(GSH-ST)in HD group was significantly lower than that in LD and MD groups on day 90(P<0.05).Catalase activity(CAT)and malondialdehyde(MDA)content did not show significant differences in the whole time period,but MDA content continued to accumulate in fish over time.The results showed that the stress caused by culture density could inhibit the antioxidant capacity of juvenile hybrid sturgeon to some extent.(3)By RNA-Seq sequencing of muscle tissue,60.70Gb of Clean Data were obtained,and the Clean Data of each sample reached 6.30Gb,and the percentage of Q20 and Q30 bases were above 97.45%and 93.42%.The comparison efficiency was72.64%～74.38%when the genomes of Acipenser sturgeon were used as reference genomes.A total of 15,549 new genes were identified based on the genome of the sturgeon.After annotation of new genes,12,636 new genes were annotated and 2913new genes were not annotated,which greatly enriched the content of the genome.A total of 611 non-redundant differentially expressed genes(DEGs)were obtained by pair comparison of the three density groups,and 33 DEGs were common between the LD vs HD and LD vs MD comparison groups.LD vs HD and MD vs HD comparison groups had 40 DEGs in common;There were 31 DEGs in LD vs MD and MD vs HD comparison groups.Only one DEG is common to all three comparison groups.GO functional enrichment analysis showed that the main enrichment was the increase of GTPase activity,myosin complex,and muscle motility Protein binding,ATP binding,zinc ion binding and other secondary nodes.Among the secondary nodes associated with growth,some differentially related genes were identified.The most representative ones were growth hormone receptor,transforming growth factorβ-2and Wnt1 inducible signaling pathway protein 1,insulin-like growth factorⅠand alpha,α-1,6-mannotransferase,respectively.Heat shock proteins 70,90 and the 7th member of the DNAJ homologous subfamily C were obtained from the stress related secondary nodes.KEGG pathway enrichment analysis showed that the main enrichment pathways were glycosaminoglycan biosynthesis heparin sulfate/heparin,cysteine and methionine metabolic pathways,alanine,aspartate and glutamate metabolism,phagocyte and m TOR signaling pathways,which were closely related to basal metabolism.(4)Real-time quantitative PCR analysis of selected growth and stress related genes showed that the relative expression level of liver growth hormone receptor(GHR)gene in LD and MD groups was significantly higher than that in HD group at15d(P<0.05).On day 30,the relative expression of insulin-like growth factorⅡ(IGF-2)gene in liver of LD and MD groups was significantly higher than that of HD group(P<0.05).At 45d,the expression of GHR gene in LD and MD groups was significantly higher than that in HD group(P<0.05);The expression of insulin-like growth factorⅠ(IGF-1)gene in liver of LD group was significantly higher than that of medium and high density group(P<0.05).At 60d,the GHR gene expression level was significantly different among the three density groups(P<0.05).At 75d,the gene expression levels of GHR,IGF-1 and IGF-2 in LD group were significantly higher than those in MD and HD groups(P<0.05).On day 90,the expression levels of GHR and IGF-2 gene in LD group were significantly higher than those in MD and HD group(P<0.05),and there were significant differences in IGF-1 gene among the three groups(P<0.05).On day 15,the liver heat shock protein 70(HSP70)gene expression in LD group was significantly lower than that in MD and HD groups(P<0.05).On day 30,the liver heat shock protein 90(HSP90)gene expression in LD group was significantly lower than that in MD and HD groups(P<0.05).At 45d,the expression of HSP70 in LD group was significantly lower than that in MD group(P<0.05);The expression of HSP90 gene in LD group was significantly lower than that in MD and HD groups(P<0.05).After 60 days,the expression levels of HSP70 and HSP90 in LD group were significantly lower than those in HD group(P<0.05),and the relative expression levels of HSP90 at 60 and 90 days were significantly different between the three density groups(P<0.05).In conclusion,different culture densities have limited effects on the growth of juvenile Siberian hybrid sturgeon at the early stage of culture,but at the later stage of culture,the higher the density,the greater the effects on the growth,body composition,antioxidant capacity and stress of juvenile sturgeon,namely,the HD group>MD group>LD group.In conclusion,juvenile Siberian hybrid sturgeon showed good growth performance under medium and low density test conditions.Therefore,it is recommended to control the medium and low density density(0.465 kg/m~2-0.694kg/m~2)of juvenile Siberian hybrid sturgeon in water culture in Jinggangshan region.