The crossbreeding activities of the Schistosoma mansoni vector snail Biomphalaria glabrata were counted in a laboratory aquarium throughout the year under two regimes of 12h light: 12h dark from 7 A., M. to 10 P. M. Mating increased significantly in Authmn and Winter and just missed a significant inverse correlation with temperature and a direct one with locomotion. Other similar experiments were carried out to compare mating under various ilumination conditions in complete daily cycle measurements. Mating counts decreased under the regimes which submited snail to a total exposure of 12h light and 12 dark during a daily cycle in the following sequence: 12h light: 12h dark alternating hourly with light gradient, 12h light: 12h dark, 1h light: 1h dark and 12h dark: 12h light. Under two constant illuminations, the mating scored less than under the previous conditions, except under 12h light. Under darkeness the mating count was lower than light conditions. There was no way to differentiate the night and day rhythms of mating on different days in each regime, except for mating under 12h light: 12 dark alternating with light gradient, constant dark and 12h dark: 12h light conditions. Mating increased in certain light and temperature conditions, in wich the intensities, should have an optimum value.

A frequência de descargas do órgão elétrico {DOE) de um peixe gymnotiforme de freqüência "em pulso" (40-100 Hz) da América do Sul - Rhamphicthys rostratus - foi estudada. Os animais foram colocados aos pares em aquários e depois observados: variação da freqüência do DOE tinha sido menor duas componentes: uma mais positivamente correlacionada devido a interação social.

The frequency of electric organ discharges (EOD) of a gymnotiform fish of "pulse" frequency (40-100 Hz) from South America - Ramphicthys rostratuswas studied. The animals were settled in pairs in a aquarium and thus observed: variation in EOD frequency had at least two components: one more positively correlated with temperature, another less positively correlated due to social interaction.

Resumo Após fazer-se um estudo sobre aspectos gerais de familias, gêneros e algumas espécies de Gymnotoidei e outros peixes elétricos amazônicos, bem como sobre seus habitats e hábitos de vida, analisam-se os órgãos elétricos e respectivas descargas em várias espécies. Procuram estabelecer-se as funções da descarga do órgão elétrico. (DOE) na vida do animal, correlacionando-se a mesma com o comportamento e outros eventos. Em seguida, estuda-se a eletrorrecepção, seus órgãos dos sentidos especiais e processamento cerebral, inclusive o uso de eletrorrecepção por peixes não elétricos. Conclui-se o trabalho, Interpretando-se o possível significado ecológico e prático dos fatos observados.

Summary An overview of the families, genera and some species of the Gymnotoidei is presented with a review of their behaviour and natural history. Characteristics of the electric organs and electric organ discharge (EOD) for various species are presented. The role of EOD on the animal's life is discussed, especially as it relates to behaviour and other events. Electroreception, its special sense organs and brain-processing, including use by non-electric fish is discussed. The results of these studies are interpreted in terms of their pratical and ecological significance in the life of this group of fish.