Population ecology of Red-bellied Piranha Pygocentrus nattereri Kner, 1858 (Characidae: Serrasalminae) in the Negro River, Pantanal, Brazil

摘要

This study defined some population parameters for growth of the Red-bellied Piranha (Pygocentrus nattereri) in the Pantanal, based on the bimonthly length-frequency distribution of individuals in samples taken from October 2005 through August 2008 in the Negro River. The samples were taken by means of gill nets and cast nets, with meshes of 1.5–8 cm between adjacent knots. The standard length of the fish ranged from 10.2 to 30.2 cm with a mean of 20.51 ± 3.39. The gonadosomatic index (GSI) varied significantly among months (F = 5.45; p < 0.01), it was significantly higher from October to February, and was positively correlated and synchronized with day length (rs = 0.92; p < 0.01) and rainfall (rs = 0.70; p < 0.01). It was desynchronized from and not correlated with river level (rs = 0.12; p = 0.69). The GSI reached the highest values and ripe individuals were more frequent in December, prior to the months of highest river levels from February to April. The estimated growth parameters were L∞ = 31.8; k = 0.45; Rn = 0.204. In the Pantanal, P. nattereri has a life expectancy (6.9 years) compatible with the 7 cohorts indicated by the growth curve. Sexual maturation occurred at around 15.4 cm, after 1.6 years.