Ontogenic changes in digestive tract and diet of Trachelyopterus galeatus

Abstract

In order to analyze aspects of the initial diet of Trachelyopterus galeatus (Linnaeus, 1766) (Pisces, Auchenipteridae) larvae and juveniles were collected monthly between October 2004 and March 2006 in Ivinheima River, MS. To characterize the morphology of the digestive tract (mouth and digestive tract) and diet, individuals were classified in different stages of development, measured and grouped into size classes. The consumed items were identified and grouped by determining the frequency of occurrence and numerical. To summarize the patterns of similarity in diet composition along the ontogenetic development, it was implemented in the matrix of the food groups Nonmetric Multidimensional Scaling (NMDS). The difference between size classes (factor) was determined using a Permutation Analysis of Variance (PERMANOVA main test). Larvae of T. galeatus initially present a sub-terminal mouth, reaching terminal in post-flexion and juveniles, suggesting change in foraging position. The differentiation between the stomach and intestine was observed only in flexion stage, coinciding with the transition from endogenous and exogenous feeding. Larvae of class I fed mainly on microcrustaceans and aquatic insects, demonstrating that larvae exploited resources in marginal aquatic vegetation. For the other classes, aquatic insects dominated the diet. The NMDS and PERMANOVA identified differences in dietary composition between the classes of more distinct sizes. Thus, the morphology of the digestive tract allied to that of body, presented by the initial larvae of T. galeatus, limit the capture of food items and, therefore, influence the composition of the diet.