Delayed First Feeding Chronically Impairs Larval Fish Growth Performance, Hepatic Lipid Metabolism, and Visceral Lipid Deposition at the Mouth-Opening Stage.

During the mouth-opening stage, fish larvae are susceptible to delayed first feeding (DFF). In this study, we explored the effects of DFF for two days on later growth and energy metabolism in larval fish. Results showed that DFF chronically impaired larval growth performance, thereby reducing the efficiency of feed utilization by larvae. In DFF larvae, the mRNA levels of growth inhibitors (i.e., igfbp1a and igfbp1b) were significantly upregulated and consistently maintained at high expression levels, which may be an important attribution of larval growth retardation. Concomitantly, DFF retarded the growth of adipose tissue and reduced lipid deposition in larval viscera, suggesting lipid metabolism is disordered in DFF larvae and generates inefficient lipid reserves. In the liver, we observed that DFF resulted in a significant accumulation of neutral lipids, and this phenotype did not disappear rapidly after DFF larvae received exogenous nutrition. As to the transcript analyses, we found that the expression of genes related to hepatic lipid synthesis (e.g., srebf1, srebf2, dgat1a, dgat1b, fasn, and scdb) in DFF larvae was consistently upregulated, while the expression of genes involved in lipid transport (e.g., apoa2, apoa4b.1, and apoa4b.3) was downregulated. Therefore, it appears that the inefficient lipid reserves in DFF larvae are associated with their hepatic lipid transport dysfunction. Taken together, our findings contribute to understanding the impairments to fish larvae caused by delayed first feeding during the mouth-opening stage and to aiding larval management in the aquaculture industry.