Differential digestive and metabolic profile of juveniles and adults of the estuarine-dependent marine fish Mugil liza (Mugilidae) cohabiting inside a southwestern Atlantic coastal lagoon

Integrative studies on intraspecific differences of digestive enzymes, energy reserves and morphological/somatic traits in juveniles and adults of estuarine-dependent marine fish while inhabiting inside a coastal lagoon are lacking. This study was carried on juveniles and adults of Mugil liza (Valenciennes, 1836) inhabiting inside Mar Chiquita Coastal Lagoon (Argentina). Both stages exhibited amylase, maltase, sucrase, lipase, trypsin and aminopeptidase-N (APN) activities in the intestine, which were active over a wide range of pH and temperature and exhibited Michaelis-Menten kinetics. Adults exhibited higher intestinal coefficient (31%), higher amylase (32%) and lower maltase (82%) and lipase activities (38%). Glycogen concentration in liver and muscle was similar while free glucose concentration was higher in adults (772% and 400% respectively). In adults retroperitoneal fat (absent in juveniles) constituted the main triglycerides storage site, while triglycerides concentration in liver and muscle was lower (86% and 80% respectively) than in juveniles. No differences were found in protein concentration in any storage organ. The results show that juveniles and adults exhibit a digestive and metabolic profile at the biochemical level and intraspecific differences in key components of carbohydrate and lipid metabolism that could support preparation for reproductive migration of adults outside the coastal lagoon.