Biology of the electric eel, Electrophorus electricus, Linnaeus, 1766 (Gymnotiformes: Gymnotidae) on the floodplain of the CuriaA0 River, eastern Amazonia

The evaluation of the growth patterns and reproductive strategies of fish species are vitally important for the understanding of their biology and the management of stocks. The present study focused on the Amazonian electric eel (Electrophorus electricus), which is capable of producing an electrical discharge of up to 800 V. Specimens were collected on a monthly schedule from a floodplain in the eastern Amazon basin. The gonads of these specimens were examined, and the sex ratio, growth parameters, population structure, body size at first gonadal maturation, and the gonadosomatic index were determined. A balanced sex ratio was found. Males were larger than females, and both sexes presented isometric growth, which is unusual in species with an elongated anatomy. This isometry may be related to the reduction of the coelomic cavity, and its position near the head. The spawning period coincided with the start of the rainy season, and continued until high water, with the variation in gonadal development following the fluctuations in precipitation and river water levels. The asymptotic body length in both sexes was relatively large, and was inversely related to the growth coefficient (k), with a slower growth rate being recorded in the males. Mortality rates were relatively low in comparison with most species of tropical fish. The larger size of the male may be related to their role in parental care, and sexual selection on the part of the females. These findings may be important for the management of wild stocks, as well as captive rearing.