Ecologia alimentar de Characidium vidali Travassos, 1967 no Rio Macaé (RJ) revelada através de quatro ferramentas complementares

Abstract

The trophic ecology of Characidium vidali Travassos 1967 (Characiformes; Crenuchidae) from Macaé River (Rio de Janeiro State, Southeastern Brazil), is described through stomach contents analysis (SCA), analysis of δ13C and δ15N stable isotopes (SIA), ecomorphology (EM) and underwater observations (UWO). Specimens were collected between March/2004 and March/2005 (SCA and EM), and between March/2009 and November/2010 (SCA and SIA) in three sites located within the upper and intermediate stretches of Macaé River. For SIA, basal resources (epilithon, periphyton, terrestrial plants and macrophytes) and aquatic insects were also sampled. Food items identified in the stomach contents were counted and had the length and volume measured. The diet was characterized using the Index of Relative Importance (IRI), niche breadth (Simpson) and feeding strategy (graphical inspection method). A total of 36 food items were identified, being 35 autochthonous. Characidium vidali consumed a high richness of aquatic insects in similar proportions, both in the spatial (along the river) and temporal (seasonal) axes (Pianka Overlap Index). Chironomidae, Simuliidae and Baetidae were the most important items according to IRI. The species was classified as a generalist, with a large niche breadth. A mixing model (IsoSource 1.3.1) was used to determine the most assimilated food items by C. vidali and aquatic insects. Autochthonous Carbon was revealed as the most important for the aquatic insects, hence for C.vidali. 13C signatures in fish muscle were significantly different among sites, indicating different assimilation along the river. Palatability, estimated by C:N ratio, was higher for periphyton and Lepidoptera. Despite Chironomidae was the most abundant item, it was not the most assimilated in all sampling sites. Trophic position (TP), calculated on the basis of SAI and δ15N results, indicated that C. vidali is a secondary consumer. Sixteen morphological measurements and 11 related indices were selected in order to determine the relation between morphology and trophic behavior. The indices values obtained are similar to those found for other congeneric species. The linear regression between fish length and lenght of the two most abundant prey showed no selection of larger prey as fish grow larger; however, smaller individuals consume only smaller-sized prey, probably due to morphological constraints, probably related to mouth opening size. For underwater observations the focal animal sampling was employed, revealing C. vidali as a rather benthic species that lives in riffles of moderate to strong flow, on rocky substrates further from the margins, and uses the “Sit-and-wait predation” foraging tactic. The four methods employed were satisfactory to characterize the feeding ecology of C. vidali.