Parâmetros populacionais, período reprodutivo e crescimento de prochilodus lineatus (characiformes, prochilodontidae) na cabeceira do Rio Miranda, Alto Rio Paraguai

Abstract

In the present paper we analyzed growth parameters, length-weight relationship and the influence of seasonal variation of Miranda river, upper Paraguay River, on breading season of Prochilodus lineatus. The samples were accomplished monthly from April/2000 to October/2003. The length-weight relationship described for females was PT=0.01213*CP3.039 and for males was PT=0.01322*Ct3.012. The estimated asymptotic total length was 55.68cm and the growth rate K = 0.46 and Rn = 0.183 were estimated by frequency of length classes. The estimated size at first maturity (L50) was 28.2cm. The gonadossomatic index (GSI) varied significantly among months (H = 136.61; p < 0.01), with significant higher values from September to December, however ripe females were caught from August to February. GSI was positively correlated with the day length (rs = 0.55; p < 0.05) and with rainfall (rs = 0.65; p < 0.05), however, it was not correlated with the river level (rs = 0.48; p = 0.1). The increasing in the duration of the day and the begin of the first rains seem to act as cues for females start the breeding activity, in order to provide to eggs and larvae the optimum environmental conditions that will be found in subsequent flooded months. This fact was verified by the greater proportion of ripe females from September to December. The life expectancy of 6.5 years was compatible with the 6 cohort estimated by the growth curve.