Metabolic strategy and appetite regulation of Japanese eel ( Anguilla japonica ) subjected to long‐term food deprivation: Physiological adaptation and survival implication

This study examined the effects of different food deprivation periods (0, 7, 14, 28, 42, and 84 days) on physical indexes, appetite gene expression, physiological and biochemical levels and intestinal histology in Japanese eel ( Anguilla japonica ). A total of 240 elvers (3.87 ± 0.06 g) were randomly divided into a starvation group (SG) and a feeding group (FG). The results showed that SG exhibited significant declines in body weight, condition factor, and hepatosomatic index with prolonged starvation. During the starvation period, appetite‐related genes exhibited dynamic regulation. Compared to FG, the mRNA expression of neuropeptide Y ( npy ) and ghrelin in SG increased significantly at days 7, 28, and 84, while corticotropin‐releasing hormone ( crh ), pro‐opiomelanocortin ( pomca ), cholecystokinin ( cck ), and peptide YY ( pyy ) decreased significantly at days 7, 14, and 84. Superoxide dismutase and catalase activities in SG peaked at days 7 and 14, respectively, significantly higher than FG, but declined below FG by day 84. Additionally, malondialdehyde levels increased by 85.46% and total antioxidant capacity decreased by 62.88% in SG at day 84 compared with FG. Intestinal histology revealed villus atrophy, goblet cell loss, and structural damage during prolonged food deprivation, while digestive enzymes (protease, amylase, and lipase) in SG were significantly lower than FG. Metabolically, SG exhibited significantly lower glucose and serum triglyceride levels than FG at the 84th day, whereas hepatic cholesterol content was markedly elevated. Furthermore, liver glycogen and muscle glycogen in SG gradually declined, reaching the lowest level at the 84th day. These findings highlighted a specific adaptation strategy, characterized by glycogenolysis and antioxidant activation during short‐term starvation, while long‐term food deprivation led to metabolic collapse, oxidative damage, and intestinal dysfunction. This study elucidated survival strategies under nutritional stress, offering insights for optimizing feeding regimes in A. japonica farming.