Hepatic morphology and serum biochemical profile according to dry and rainy seasons in <i>Pygocentrus nattereri</i> (Characiformes: Serrasalmidae)

This study investigated the physiological and morphological adaptations of the liver of the carnivorous fish Pygocentrus nattereri (piranha) in response to seasonal variations (dry and rainy seasons) in the Brazilian Pantanal. The objective was to describe how the liver, a central organ in metabolic regulation, responds to environmental changes and test the hypothesis that seasonal variations promote significant changes in enzyme levels and cellular morphology. Adult specimens (20 per season, equally distributed by sex) were analyzed for biometrics, biochemistry (glucose, triglycerides, ALT, AST, urea, creatinine, and bilirubin), and liver histology. Results showed that levels of triglycerides, ALT, AST, and urea were significantly higher during the rainy season, indicating increased metabolic activity, which correlates with higher food availability. Hepatic tissue showed sexual dimorphism during the rainy season: males exhibited larger, more vacuolated hepatocytes (suggesting lipid accumulation), while females had more granular cytoplasm, likely associated with vitellogenin synthesis. The integrative data analysis (bgPCA) confirmed distinct groupings by sex and season. In conclusion, P. nattereri demonstrates adaptive physiological plasticity to the environmental fluctuations of the Pantanal, with changes in biochemical biomarkers and liver morphology providing valuable insights into this species' adaptive mechanisms.