Insights into the molecular response mechanisms of fasting stress and refeeding in channel catfish (Ictalurus punctatus) through transcriptome and histological analysis.

Throughout their life cycles, many fish alternate between periods of fasting and feeding due to the temporal and geographical variability of food availability in aquatic environments. The ability to adapt to fasting and restore internal balance after refeeding is fundamental to the long-term survival and symbiotic relationships of aquatic species. However, our understanding of the mechanisms by which the fish adapt to fasting and refeeding remains limited. We looked at the growth performance, intestinal and liver histology, and liver gene expression patterns of channel catfish, a significant commercial species, during three weeks of fasting stress and three weeks of refeeding, respectively, in order to clarify the molecular response mechanisms to these two events. Our study revealed that fasting significantly impacts growth, histological characteristics and physiological metabolism. During the fasting period, catfish growth performance was greatly inhibited, but growth compensation was observed after refeeding. Histological analysis showed that liver and intestinal tissues experienced varying degrees of apoptotic injury during fasting, with a modest number of TUNEL-positive cells still present in the liver after refeeding. We identified 787 significant differentially expressed genes (DEGs) in the control group in three weeks (CG3) groups versus the fasting-refeeding group inthree week (EG3) group, while only 35 DEGs were defined in the CG6 group versus the EG6 group. Gene Ontology functional annotation and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses suggested that fasting stress affected gene expression related to the mitotic cell cycle, cell cycle processes, amino acid metabolism, steroid biosynthesis, fatty acid metabolism and immune responses. Metabolism and cellular process response genes were significantly downregulated in the fasting group. Significant alterations in the expression levels of genes related to metabolism and apoptosis were validated by quantitative Real-time PCR (qRT-PCR). This study provides insights into the physiological mechanisms underlying fish adaptation to fasting or nutritional deficiency stress, shedding light on how channel catfish respond to fasting stress and refeeding.