Nutrition dynamics of "tambiú” Astyanax bimaculatus Linnaeus, 1758 (Pisces, Characiformes, Characidae) in Ibitinga Reservoir, São Paulo State, Brazil

Abstract

Respecting to Astyanax bimaculatus in Ibitinga Reservoir, seasonal variations of average index of stomach repletion (r), condition factor (Ñ"ž) and reIative frequency of repletion stages (fr) were analyzed. From July/1989 to June/1990, 704 individuals (379 females and 325 males) were examined. When males and females were considered together, relative frequency of demi-full stomachs remained around 50% during the year; the lowest frequency of full stomachs, which was close to the highest frequency of the empty ones, occurred in springs, and the highest, in autumn (in contrary progression relatively to that one observed for empty stomachs frequencies), when the condition factor has been maximum, after reaching its minimum in spring, what emphasizes the period of reproduction activity. When females were considered separately, full stomachs frequencies were higher in summer (maximum level) and autumn, and the minimum one occurred in spring, when demi-full stomachs frequency has been highest and both average index of stomach repletion and condition factor were lowest what evidentiated again the period of reproduction process