Age and growth of Hypophthalmus edentatus (Spix), (Siluriformes, Hypophthalmidae) in the Itaipu Reservoir, Paraná, Brazil

Abstract

Age and growth of Hypophthalmus edentatus (Spix, 1829) (Siluriformes, Hypophthalmidae) was determined. Data were collected from December 1983 to November 1984 and from April 1997 to March 1998 in the Itaipu Reservoir. To evaluate reading consistency, it was analyzed the coefficient of variation of the total length for each annulus observed in the otoliths. Through marginal increment analysis, it was determined that the annuli formed annually (April) indicating that otoliths may be used in the study of age and growth of the species. Food supply was considered the main factor affecting growth and annuli formation in both periods. Back-calculated data were used to assess if the Rosa Lee phenomenon, commom in selective samples like commercial fishing, occured. It was used also, the von Bertalanffy model to obtain the length growth curve. Parameters k and L (∞); were estimated by nonlinear regression for sexes separated. Although nom significant, k was greater in 1983-1984 than in 1997-1998. Inversely the L(∞); was greater for females, but k was smaller. Age at first maturation and annual instantaneous mortality (A) were similar in both sexes and years analyzed.