Changing dietary preferences in very young Trachelyopterus galeatus

[bekateen]

Santin, M., Lopes, T.M., Baggio, M.M., Agostinho, A.A., & Bialetzki, A. 2015. Mudanças ontogênicas no trato digestório e na dieta de Trachelyopterus galeatus. Bol. Inst. Pesca, São Paulo, 41(1), 57-68

Santin, M., Lopes, T.M., Baggio, M.M., Agostinho, A.A., & Bialetzki, A. 2015. Ontogenic Changes in the Digestive Tract and Diet of Trachelyopterus galeatus. Bol. Inst. Pesca, São Paulo, 41(1), 57-68

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, 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 more distinct size. Thus, the morphology of the digestive tract, allied to body, presented the initial larvae of T. galeatus limit the capture of food items and therefore influences the composition of the diet.

Keywords: cangati; ichthyoplankton; feeding; Ivinheima river

Developmentally, the subjects were grouped into size classes, with size classes defined by standard length ranges:

• Class I (5.83 to 8.84 mm; stages of pre-bending and initial bending)
• Class II (8.85 to 11.86 mm; bending stage)
• Class III (11.87 to 14.88 mm; the final bending stage and post-flexion)
• Class IV (14.89 to 20.28 mm, post-bending stage end and juveniles)

Among other conclusions, the authors found that smaller, less developed individuals had a different diet than older juveniles:

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. (emphasis added)