FEEDING DYNAMICS OF OLIGOSARCUS JENYNSII (G√úNTHER, 1864) IN A SUBTROPICAL COASTAL LAKE ASSESSED BY GUT-CONTENT ANALYSIS AND STABLE ISOTOPES
|Lúcia Ribeiro Rodrigues1*, Nelson Ferreira Fontoura2 and David da Motta Marques1
|Corresponding Author: Lúcia Ribeiro Rodrigues, Laboratório de Ecotecnologia e Limnologia, Instituto de Pesquisas Hidráulicas, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970, Porto Alegre, RS, Brazil. E-mail: email@example.com|
|Received: 12 December 2011 Accepted: 27 February 2012|
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The present study aimed to identify the seasonal feeding dynamics of two size classes of Oligosarcus jenynsii (< 14 cm total length and > 14 cm total length) using stomach content analysis and stable isotope analysis of carbon and nitrogen. Sampling was carried out seasonally, from winter 2006 to autumn 2007 in the northern part of Mangueira Lake, southern Brazil. Palaemonetes argentinus (Crustacea, Decapoda, Palaemonidae) was the prey type most frequently observed in the stomachs of O. jenynsii. However, the dominant prey type changed with season and size class. Terrestrial insects (Coleoptera, Hemiptera and Hymenoptera) were important for both size classes in the winter and summer, and Aegla prado (Crustacea, Decapoda, Aeglidae) were important in the spring for fish > 14 cm. Individuals > 14 cm ingested more crabs (A. prado) and terrestrial insects and fewer prawns (P. argentinus). Stable isotope analysis indicated that O. jenynsii from both size classes was similar in δ15N, but the δ13C signature varied with size class, with individuals > 14 cm more depleted in 13C, suggesting different carbon pathways. Larger individuals may have obtained their carbon from macrophytes or allochthonous sources, whereas smaller individuals were likely supported by periphyton and P. argentinus.