The family Mugilidae consists mainly of diadromous species, whose reproduction occurs in offshore waters. Pre-juveniles shift their diet in the surf zone (zooplanktophagous to iliophagous). Later, during their recruitment into estuaries, huge changes take place in their digestive system. However, digestive and metabolic characteristics and some morphological traits at recruitment are unknown for Mugilidae. We performed comparative studies on early and late pre-juveniles of Mugil liza recruited in Mar Chiquita Coastal Lagoon (37 32 0-37 45 0 S, 57 19 0-57 26 0 W, Argentina). We determined digestive enzyme activities (intestine), energy reserves (liver/muscle), total/standard length, total weight, intestinal coefficient, hepatosomatic index and retroperitoneal fat. Pre-juveniles exhibited amylase, maltase, sucrase, lipase, trypsin and aminopeptidase-N (APN) activities, which were maintained over a wide range of pH and temperature, and exhibited Michaelis-Menten kinetics. In late pre-juveniles, amylase (422 ± 131 μmol maltose min −1 mgprot −1), sucrase (86 ± 14 mg glucose min −1 mgprot −1), trypsin (84 ± 9 μmoles min −1 mgprot −1) and APN (0.58 ± 0.08 μmoles min −1 mgprot −1) activities were higher (42%, 28%, 35% and 28%, respectively) than in the early stage. Also, the intestinal coefficient was higher in late (3.04) compared to early (2.06) pre-juveniles. Moreover, the liver appeared to be a main site of glycogen and triglyceride storage in late pre-juveniles, muscle being the site of storage in early pre-juveniles, exhibiting higher glycogen, free glucose and protein concentrations (92%, 82%, 32%, respectively). The results suggest that pre-juveniles of M. liza exhibit an adequate digestive battery to perform complete hydrolysis of various dietary substrates, availability of energy reserves and morphological characteristics to support their feeding habit and growth after recruitment. Our results represent an important contribution to knowledge of the ecology and digestive physiology of pre-juveniles of Mugilidae in the wild. K E Y W O R D S digestive enzymes, energy reserves, Mar Chiquita Coastal Lagoon, Mugil liza, pre-juveniles, recruitment Mariano González-Castro and Alejandra López-Mañanes have contributed equally to this study.

The hepatopancreas of decapod crustaceans is an organ which can act as indicator for digestive and metabolic parameters under different physiological and / or environmental conditions. However, biochemical studies on digestive and metabolic parameters of the hepatopancreas of euryhaline burrowing crabs such as Neohelice granulata from habitats with different diet compositions are still scarce. In the wild, adult males of N. granulata from Mar Chiquita Coastal Lagoon (Argentina) in mudflat habitat have diets with higher lipid and protein content than crabs from the saltmarsh, suggesting that diets could be an important factor influencing hepatopancreas activities. We tested this hypothesis here by exposing adult male crabs to a similar experimental diet and comparing hepatopancreas parameters for lipid components and protein metabolism between males from these two habitat types at different times (up to three months). At month 3, we noticed a decrease of the triglyceride concentration and lipase activity and an increase of protein concentration in crabs from the mudflat. In contrast, triglycerides and protein concentration did not change in crabs from the saltmarsh, while lipase activity decreased and levamisole insensitive AP increased at month 3. The results indicate that digestive and metabolic parameters in the hepatopancreas of crabs from habitats varying in diet content remain different, even if crabs are subsequently fed by a similar experimental diet. This suggests that specific intrinsic regulations of these hepatopancreas parameters could operate differently in each habitat and could not be changed by recent diet conditions.