Influence of Eichhornia crassipes and Lemna sp. on the natural diet of Astyanax altiparanae Garutti Britski, 2000 in the initial stages/Influencia de Eichhornia crassipes e Lemna sp. na alimentacao natural de Astyanax altiparanae Garutti Britski, 2000 na fase inicial

Aiming to study the changes in the diet of Astyanax altiparanae in the early developmental stages, in the presence of Eichhornia crassipes (EC) and Lemna sp. (LM), larvae of Astyanax altiparanae were stocked in eight tanks of 900 L (500 ind. [tank.sup.-1]), four with EC and four with LM covering 50% surface. Tanks were inoculated with plankton and received 3.0 g inorganic fertilizer (NPK-7:14:8) and 1.5 g every week. At every three days, three larvae were taken from each tank, fixed in 4% formaldehyde and grouped into four age classes (I: 6 to 12 days, II:15 to 21 days, III:24 to 30 days; IV:33 to 39 days). The analysis of dominance and frequency of occurrence (FO) of food items indicated that, at this stage, A. altiparanae is generalist. In class I, there was a greater dominance and FO of Lecane bulla and Alona sp. in digestive tracts in the presence of both EC and LM, respectively; and larvae started to consume larger organisms, such as Chironomidae, in other age classes with EC. In the presence of LM, Alona sp. was dominant in class II; Chironomidae, in class III and Centropyxis sp., in class IV. Diatoms have greater FO both in EC and in LM. In class III, with EC, Chironomidae had higher FO, as well as Arcella sp. and Scenedesmus spp. with LM. The highest FO in class IV was found for L. bulla and Scenedesmus spp., with EC and LM, respectively. It can be concluded that EC and LM influenced the diet of Astyanax altiparanae, with alterations according to the availability of organisms and increase in age. Keywords: fish larvae, floating macrophyte, plankton, larval development, diet. Objetivou-se estudar mudangas da dieta nos estagios iniciais de desenvolvimento de Astyanax altiparanae, na presenga de Eichhornia crassipes (EC) e Lemna sp. (LM). Larvas de Astyanax altiparanae foram estocadas em oito tanques de 900 L (500 ind. [tanque.sup.-1]), sendo quatro com EC e quatro com LM cobrindo 50% da superficie destes. Os tanques foram inoculados com plancton e receberam 3,0 g de fertilizante inorganico (NPK-7:14:8) e 1,5 g semanalmente. A cada tres dias foram coletadas tres larvas de cada tanque, fixadas em formol a 4% e agrupadas em quatro classes de idade (I: 6 a 12 dias, II: 15 a 21 dias, III: 24 a 30 dias e IV:33 a 39 dias). Relacionando a dominancia e frequencia de ocorrencia (FO) dos itens alimentares verificou-se que, nesta fase, o A. altiparanae e generalista. Na classe I, houve maior dominancia e FO de Lecane bulla e de Alona sp. nos tratos digestorios n