The population structure, reproductive aspects and feeding of Phalloceros caudimaculatus (Hensel, 1868), Poecilia vivipara Bloch & Schneider (1801), Phalloptychus januarius (Hensel, 1868) e Jenynsia lineata (Jenyns, 1842) were studied in five sampling stations in the Ubatiba stream, municipality of Maricá (State of Rio de Janeiro, Brazil). In relation to the population structure, P. caudimaculatus was more representative upstream; P. vivipara mid-stream and downstream; P. januarius and J. lineata downstream. The species presented preponderance of females, except in the intermediate length classes. The occurence of imatures and females with young pointed out a long reproductive period and favoured areas for reproduction of the four species. The young forms of P. caudimaculatus were more abundant in station 1 (upstream), P. vivipara in station 4 (downstream) and P. januarius and J. lineata in station 5 (Maricá coastal lagoon). The higher occurences of females with young belong to P. caudimaculatus, in station 1 (upstream) and P. vivipara and P. januarius in station 5 (Maricá lagoon). The four studied species presented herbivorous diet and the differences found in the feeding may reflect the differences in the food availability in the microhabitats used by the species. So, we concluded that the studied species presented evident segregation in several levels of the different available resources in the environment.
Cyprinodontiformes; population structure; feeding; reproduction; coastal stream