Hepatic steatosis caused by starvation, resulting in non-alcoholic fatty liver disease (NAFLD), has been a research topic of human clinical and animal experiments. To understand the molecular mechanisms underlying the triggering of abnormal liver metabolism by starvation, thus inducing hepatic lipid accumulation, we used zebrafish larvae to establish a starvation-induced hepatic steatosis model and conducted comparative transcriptome analysis by RNA-seq. We demonstrated that the incidence of larvae steatosis is positively correlated with starvation time. Under starvation conditions, the fatty acid transporter (slc27a2a and slc27a6-like) and fatty acid translocase (cd36) were up-regulated significantly to promote extrahepatic fatty acid uptake. Meanwhile, starvation inhibits the hepatic fatty acid metabolism pathway but activates the de novo lipogenesis pathway to a certain extent. More importantly, we detected that the expression of numerous apolipoprotein genes was downregulated and the secretion of very low density lipoprotein (VLDL) was inhibited significantly. These data suggest that starvation induces hepatic steatosis by promoting extrahepatic fatty acid uptake and lipogenesis, and inhibits hepatic fatty acid metabolism and lipid transport. Furthermore, we found that starvation-induced hepatic steatosis in zebrafish larvae can be rescued by targeting the knockout cd36 gene. In summary, these findings will help us understand the pathogenesis of starvation-induced NAFLD and provide important theoretical evidence that cd36 could serve as a potential target for the treatment of NAFLD.

To investigate the effects of different raising environments on the flesh quality, the study set up three groups of silver carp (Hypophthalmichthys molitrix), that is, pond-farmed; short-term stocked; and ranched, grown in a natural water ranch. This study compared the differences in muscle proximate composition and amino acid composition among three groups. The results showed that there was no difference between the ranched and the stocked groups in content of crude protein, ash, total amino acids (TAA), essential amino acids (EAA), and umami-flavored amino acids (UAA), with both groups being significantly higher than the farmed group. This shows that, in terms of flesh quality, the stocked group was closer to the ranched group and better than the farmed group after being stocked in natural water for 30 days. The results suggest that the flesh quality of farmed fish was improved by short-term stocking in natural water. To elucidate the reasons of flesh quality change in the stocked group, this study compared the food composition and intestinal digestive enzyme activity in three groups, demonstrating that the ranched and stocked groups had similar food composition, with their detritus proportion lower than that of the farmed group, consuming easily digestible phytoplankton diatoms rich in amino acids and fatty acids. No significant difference was seen between the ranched group and the stocked group, for which amylase, lipase, and trypsin activities were lower than that of the farmed group. It is hypothesized that differences in environmental and food composition resulted in lower digestive enzyme activity in the ranched group and the stocked group. In summary, the short-term stocking of farmed fish in a natural water ranch can effectively improve the nutrient content, quality and flavor, and promote value of fish products.

Mandarin fish (Siniperca chuatsi) is a commercially important species in China. The number of pyloric caeca, essential for digestion and nutrient absorption, varies considerably (198–386) among individuals, but its relation to growth remains unclear. In this study, 300 samples from the first filial generation (F1) of farmed wild stocks were reared for 56 days and grouped based on pyloric caeca number. Fish with more pyloric caeca (≥289) exhibited significantly higher weight gain rates (WGRs), specific growth rates (SGRs), and digestive enzyme activities compared to those with fewer caeca (≤229). The final body weight (FBW) and the WGR showed moderately positive correlations with caeca number. These results showed that pyloric caeca number may be a valuable trait for selective breeding. To explore its genetic basis, a genome-wide association study (GWAS) identified over 1.4 million SNPs across 24 chromosomes. Twelve SNPs were potentially associated with pyloric caeca number, and we successfully identified one SNP that could effectively distinguish groups with the extreme number of pyloric caeca. Candidate genes near significant loci were enriched in pathways related to cell proliferation, differentiation, and metabolic regulation. These findings suggest a potential association between pyloric caeca number and growth, providing a possible reference for future molecular breeding in mandarin fish.