Digestive, metabolic, and morphological adaptations of Odontesthes argentinensis to estuarine and marine environments: insights into phenotypic plasticity and ecological differentiation

Odontesthes argentinensis inhabits both estuarine and marine environments, where differences in ecological conditions may drive metabolic and digestive adaptations. Understanding these physiological adjustments provides insight into the species phenotypic plasticity and its capacity to thrive in dynamic coastal ecosystems. This study examines how estuarine and marine populations of O. argentinensis adjust to their respective habitats by analyzing digestive enzyme activities, morphological parameters, and energy reserves in the liver and muscle. We compared individuals inhabiting the estuarine zone of the Mar Chiquita Coastal Lagoon (MChCL) with those residing in the coastal-marine zone adjacent to the MChCL. Notably, the estuarine population showed significantly higher intestinal enzyme activities (amylase, maltase, and sucrase), increased lipid reserves in both the liver and muscle (100 % and 380 %, respectively), and higher glycogen concentrations in the liver (450 %). These physiological shifts were accompanied by a higher intestinal coefficient and condition factor (K) in the estuarine individuals, highlighting their metabolic plasticity. Despite these adjustments, no significant differences were observed in protein concentrations or trypsin activity between populations. These findings underscore the remarkable phenotypic flexibility of O. argentinensis, allowing it to successfully inhabit estuarine environments and potentially offering new insights into how coastal fish species adapt to variable conditions. This study provides information for understanding how ecological factors influence physiological processes in aquatic species and their ability to cope with dynamic ecosystems.