Fish parasitic crustaceans are generally external parasites (ectoparasites) and belong to the group of isopods, whiteworms or copepods, being found mainly in tropical waters. The Loricariidae family is composed exclusively of freshwater fish and is distributed in Neotropical environments, mainly in South America. Parasitology studies with loricaride hosts are very incipient, being restricted to the occurrence record. The species Hisonotus chromodontus and Curculionichthys luteofrenatus of the subfamily Hypoptopomatinae present their distribution in the Tapajós basin and in tributaries, such as the Teles Pires river. All interactions of ectoparasitic crustaceans known to fish of the Loricariidae family are with species of the order Isopoda. Ecological studies on effects on the natural history of host loricarids, adaptations and specializations in the isopods that allow parasitism may show a new way of analyzing this interaction. Thus, one of the main purposes of this study is to investigate the interaction of isopod ectoparasites with their hosts, small loricarids under ecological and evolutionary aspects. For this purpose, our taxonomic objective is to describe new species of loricarid ectoparasite isopods, and if they are described species, to propose a redescription with details of the structures of taxonomic interest. And as ecological objectives to investigate the effects of parasitism on the ability to feed and reproduce from the hosts, to characterize data on the prevalence and intensity of isopod infestation in loricarids.