Understanding the early ontogenetic stages of Mugil liza (Mugilidae): Morphological traits and digestive/metabolic profile of pre‐juveniles after recruitment

Abstract

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.

Differential modulation of digestive enzymes and energy reserves at different times after feeding in juveniles of the marine estuarine‐dependent flatfish Paralichthys orbignyanus (Valenciennes, 1839)

“…However, further biochemical characterization is required to prove this point. In the intestine of the marine estuarine‐dependent mullet M. liza , sucrase and maltase activities correspond to the sucrase‐isomaltase and sucrase‐independent maltase–glucoamylase complex, respectively (Albanesi, González‐Castro, & López‐Mañanes, 2021). The sharp increase in maltase and sucrase activities in the intestine of juveniles of P. orbignyanus at 24 h post‐feeding suggests a temporary modulation of these activities, which could result in an increase in the ability for the last stages of dietary carbohydrate hydrolysis.…”

“…This, in turn, could result in a major provision of available glucose. In several fish species, including juveniles of P. orbignyanus , the liver is paramount to maintaining glucose homeostasis (Albanesi, González‐Castro, & López‐Mañanes, 2021; Albanesi, Radonic et al, 2021; Chen et al, 2018; Polakof et al, 2012; Tseng & Hwang, 2008). The increase in glycogen concentration in the liver at 24 h post‐ingestion in juveniles of P. orbignyanus indicated this organ as a site of postprandial glycogen reserve building.…”

“…Digestive, metabolic, and morphological parameters were determined at once (time 0, t0) and at 24, 72, 360 h post‐feeding. Individuals were placed on ice until the loss of consciousness (10 min) and afterwards processed (Albanesi, González‐Castro, & López‐Mañanes, 2021; Albanesi, Radonic, et al, 2021; del Valle et al, 2016). Total length (LT), standard length (LS), and TW of each flatfish were recorded (Albanesi, Radonic, et al, 2021).…”