Estratificación espacial y comportamiento de Prochilodus scrofa en distintas fases del ciclo de vida, en la planicie de inundación del alto río Paraná y embalse de Itaipu, Paraná, Brasil

Abstract

Prochilodus species show migratory behaviour and stratified distribution in distinct environments of South American river basins. These aspects and their relationships with the development and reproductive cycle of P. scrofa from one segment of the High Paraná River, including the Itaipu Reservoir, the River and its tributaries and the floodplain at Porto Rico (23°43 S-63º10 W / 25º033 S-54º35 W) were studied from October 1986 to September 1988. Upstream displacements of adult fishes were observed in the Reservoir from March to August; downstream movements started in September. In October, a fraction of the Prochilodus stock starts its migration to reproductive areas localized upstream, in the Paraná River and its tributaries. In the lagoons occur young fishes (73 %), less 2 years old, lengths under the L50 (18,9 cm), with immature gonads (99 %); in the channels young fishes are frequent (60 %) with lengths that correspond to 1 and 2 years old, and with gonads that have not started the cyclic development (95 %); adults occur in the Paraná River (82 %) which lengths corresponding to individuals 2 years old or more; their gonads show evidences of reproductive activity (22 % maturation; 11 % reproduction) and spawning (5 % spent); in the Itaipu Reservoir only large adults occur (100 %), 2 years old or more and with theirs gonads showing imminent (25 % maturation) or recent (72 % spent) reproductive activity. The lentic (lagoons) and semi-lentic (channels) environments of the floodplain are feeding and growing homes for young fishes until 2 years old; the Itaipu Reservoir, a semi-lentic environment, is a feeding and growing area for adults; lotic environments have an important role as reproductive areas. The species thus explore lentic environments, during the first two years of its life, and as an adult occupies cyclically lotic and semi-lentic environments.