Coilia nasus is a valuable commercial migratory fish species with ecological and economic importance in China. To explore the molecular mechanisms underlying the response to food intake, the stomach transcriptomes of feeding and non‐feeding C. nasus were analysed via RNA‐seq. A total of 610,640,864 clean reads were obtained, and annotation to six databases identified 63,567 unigenes. Comparative analysis of the gene expression in feeding and non‐feeding C. nasus identified 1,968 differentially expressed genes (p < .05), including 1,180 up‐regulated and 788 down‐regulated genes. Our results showed that stomach distention activated the vagal afferent neurons, resulting in satiation. Several of the most relevant appetite genes (e.g. leptin receptor [LepR], somatostatin [SS], nucleobindin‐2 [NUCB2], 5‐hydroxytryptamine receptor [5‐HTR], growth hormone receptor [GHR]) were also involved in the regulation of food intake and led to the termination of feeding. Furthermore, significant differences were observed in the genes encoding key enzymes involved in metabolism such as the tricarboxylic acid cycle (TCA) pathways, fatty acid synthesis and glycolysis, indicating that C. nasus utilizes food for its energy and nutrient contents to support life and gonadal development. These findings provide valuable insights into the mechanisms underlying appetite and metabolic regulation in anadromous fish and create a foundation for further research on C. nasus artificial breeding and migration energetics.
In this study, we investigated the activity levels of two major digestive enzymes (pepsin and lipase) in the commercially important Japanese grenadier anchovy Coilia nasus during its upstream migration to analyse the digestive physiological responses to starvation and to analyse the influence of the water temperature on enzyme activity. Water temperature had a significant effect on pepsin activity, while long‐term starvation resulted in a significant decrease in pepsin activity. As starvation continued, however, a slight increase in pepsin activity between the Wuhu (440 river km) and Anqing (620 river km) regions may indicate that C. nasus had refeeding behaviour due to its large expenditure of energy reserves. In contrast, lipase activity was not significantly affected by the water temperature but the effect of fasting increased as much as 13% of lipase activity from the Chongming region (20 river km) to Anqing region, suggesting that the stored lipids of grenadier anchovy were mobilised to meet energy requirements of upstream migration activity and gonad development. Lipid mobilisation activated lipoprotein lipase (LPL; proteins with lipase activity) to hydrolyse triacylglycerides (TAG), which is the first step of lipid assimilation and obtained energy from fatty acids under fasting conditions. Therefore, the increased lipase activity is attributed mainly to the lipase that is involved in endogenous lipid hydrolysis. Grenadier anchovy appears to adapt to long‐term starvation during migration and the increased lipase activity may indicate a crucial effect on lipid metabolism. This study demonstrated that distinct alterations occur in pepsin and lipase activities during the spawning migration of grenadier anchovy due to exogenous nutrition and endogenous metabolism. Furthermore, it provides a basis for further research on the digestive physiology and energy metabolism in this species.
The Chinese tapertail anchovy, Coilia nasus, is a socioeconomically important anadromous fish that migrates from near ocean waters to freshwater to spawn every spring. The analysis of genomic architecture and information of C. nasus were hindered by the previously released versions of reference genomes with gaps. Here, we report the assembly of a chromosome-level gap-free genome of C. nasus by incorporating high-coverage and accurate long-read sequence data with multiple assembly strategies. All 24 chromosomes were assembled without gaps, representing the highest completeness and assembly quality. We assembled the genome with a size of 851.67 Mb and used BUSCO to estimate the completeness of the assembly as 92.5%. Using a combination of de novo prediction, protein homology and RNA-seq annotation, 21,900 genes were functionally annotated, representing 99.68% of the total predicted protein-coding genes. The availability of gap-free reference genomes for C. nasus will provide the opportunity for understanding genome structure and function, and will also lay a solid foundation for further management and conservation of this important species.
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