| The shortage of feed resources is an important factor restricting the sustainable development of aquaculture industry.The existing researches mainly focus on fish nutrition requirements,raw material substitution,and environmental protection feed development.In order to meet the needs of the transformation of the aquaculture industry from traditional extensive to industrial intelligent aquaculture,establishing and improving the scientific feeding model has become a research hotspot.The scientific feeding mode helps to increase the utilization efficiency of feed nutrients for farmed fish,obtain the best growth rate,and reduce the self-pollution of culture.And the intrinsic feeding rhythm of fish is the biological basis for establishing a scientific feeding model.Pelteobagrus vachellii is a unique economically farmed fish in China.Due to the high market value,the demand for this variety has increased significantly in recent years.In this experiment,two different feeding strategies,daytime feeding(8:00)and night feeding(20:00),were formulated based on the circadian rhythm of Pelteobagrus vachellii.The effects of feeding time on the growth,protein metabolism,and lipid metabolism of Pelteobagrus vachellii were explored through breeding experiments.RNA-Seq sequencing technology was used to sequence transcriptomes of Pelteobagrus vachellii treated with different feeding times,and differentially expressed genes(DEGs)in the two groups of samples were screened,focusing on analysis of gene expression related to protein metabolism and lipid metabolism.Therefore,the molecular mechanism of protein,lipid digestion and absorption of Pelteobagrus vachellii affected by feeding time can be explored.The main findings are as follows:1.Feeding time significantly affects the growth of Pelteobagrus vachellii.The final body weight and special growth rate(SGR)of Pelteobagrus vachellii fed at night were significantly higher than those of daytime feeding group(P<0.05).However,feed conversion rate(FCR)was significantly lower than the daytime feeding group(P<0.05).In addition,the feeding time affected the utilization of nutrients byPelteobagrus vachellii,and the apparent digestibility of crude protein and crude fat in Pelteobagrus vachellii fed at night was significantly higher than that in daytime feeding group(P<0.05).The rusult showed that a shift in feeding time can significantly improve the growth performance and feed utilization rate of Pelteobagrus vachellii.2.A total of 47,722 genes were obtained from intestine samples of Pelteobagrus vachellii by Transcriptome sequencing.Approximately 1489 differentially expressed genes(DEGs)were created for the daytime and night-time samples.Compared with the daytime feeding group,1125 DEGs were significantly up-regulated and 364 DEGs were significantly down-regulated.Cluster enrichment analysis revealed that these genes are mainly related to circadian rhythms and metabolism of lipids,proteins,and carbohydrates.Compared with the NR database,it was found that 110 DEGs were involved in the digestion,absorption,and metabolism of nutrients,and most genes were up-regulated compared to the daytime feeding group.The rusult showed that shift the feeding time from day-time(8:00)to night-time(20:00)may promote the expression of genes related to nutrient metabolism and thus contribute to the digestion,absorption,and transport of nutrients.3.The cryptochrome 2 gene was cloned by RT-PCR and RACE techniques.The cDNA sequence of the Cry2 gene of Pelteobagrus vachellii is 2752 bp,and the open reading frame contains 1803 bases and encodes 600 amino acids.Domain analysis revealed that Cry2 had a DNA photolyase domain and a flavin adenine dinucleotide binding domain.Homologous analysis showed that Cry2 was highly conserved in evolutionary analysis;evolutionary analysis showed that the Cry2 of Pelteobagrus vachellii is closely related to the Ietalurus Punetaus,and has a closer relationship with mammals and birds,indicating that it is functional.There is a certain degree of differentiation.The tissue distribution showed that it was mainly expressed in the eyes,fat,muscles and intestines.According to the analysis of rhythm,the expression level of Cry2 gene showed periodic changes in one day and night,but the peak expression levels in different tissues were different.These results indicating that it plays an important role in physiological regulation such as feeding regulation,energy balance regulation,etc.,4.Complement C7 was obtained by RT-PCR and RACE techniques.The total length of Pv-C7 mRNA was 2647 bp,encoding 818 amino acids.These include the 52 bp 5’ UTR,the 2454 bp open reading frame(ORF)and the 141 bp 3’ UTR.RT-qPCR showed that Pv-C7 mRNA was mainly expressed in the liver,spleen,intestine,and head kidney tissues of Pelteobagrus vachellii,and in the liver,head kidney,spleen,andintestinal tissues of Noctis regia.The expression of Pv-C7 mRNA was significantly increased(P<0.05).In addition,after infection with Aeromonas hydrophila,the expression of Pv-C7 mRNA was significantly up-regulated in the liver(48-96h),spleen and head kidney(12-96h)of Pelteobagrus vachellii;The expression of Pv-C7 mRNA in fish head kidney(12-48h)and spleen(12-24h)was significantly higher than that in daytime feeding group.The rusult showed that shift the feeding time from day-time(8:00)to night-time(20:00)could increased the expression of Pv-C7 mRNA and affected the immune response involving complement C7. |
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