The ecology of the freshwater prawn #Macrobrachium amazonicum has been studied in the Lower Tocantins river in 1985-86 from Cameta to the Tucurui hydroelectric dam and in the reservoir. The population of the river below the dam exhibited a mean total length of 60 mm and a maximum of 132 mm. The mean lengths displayed a seasonal oscillation correlated with adults migration and reproduction from March to July and recruitment from September to February. The global female prawns were parasited by the isopod #Probopyrus in the lower part of the river. The population of #M. amazonicum that colonized the reservoir showed different biological characteristics from that below the dam : smaller mean and maximum lengths, earlier sexual maturity, strongly female-biaised sex-ratio, reproduction in September and recruitment from January to March. No #P. bithynis isopod was collected in this area. (Résumé d'auteur
