Reproductive biology of the piranha Serrasalmus gouldingi (Fink and Machado-Allison 1992) (Characiformes: Serrasalmidae) in “drowned” rivers of the Eastern Amazon

Abstract

In many species of Neotropical fishes, reproductive patterns are influenced by fluctuations in abiotic factors such as the flood pulse, temperature, and the physical-chemical characteristics of the aquatic environment. The present study describes the reproductive biology of the piranha, Serrasalmus gouldingi, in “drowned” rivers of the region of the lower Anapu River in the eastern Brazilian Amazon basin. A total of 262 specimens were collected between July, 2010, and May, 2011, of which 113 were male and 149 female. The sex and maturity of these specimens were characterized histologically, and the sex ratio, gonadosomatic index, relative frequency of the different stages of maturity, size at first sexual maturation, and condition factor were determined and analyzed in the context of seasonal variation in river levels. Two major reproductive peaks were observed during the transitional flood and ebb periods, coinciding with a predominance of female specimens and higher frequencies of the mature, spawned, spent, and resting gonadal stages. Sexual maturity began at 12.24 cm in males and 16.33 cm in females. Positive allometric growth was associated with a decrease in the condition factor during the peaks of reproductive activity, which occurred prior to the principal fluctuations in local river levels.