Ethnotaxonomy seeks to understand how people identify, name, and classify living organisms, associating traditional and scientific knowledge. We examined the ethnobiological and ethnotaxonomic classification systems of fishermen in relation to naming commercial fish at the Tamandaré and Batoque beaches on the northeastern coast of Brazil. Seventy-five fishermen were interviewed between January and August of 2013. The interviews concentrated on the morphological, ecological, and sociocultural criteria used in identification, naming, and classification. Fishermen mentioned 441 popular fish names, representing 268 scientific taxa. Of these, 58% were named based on morphological characteristics using folk terminology. Seventy-two generic monotypes, 42 generic polytypes, and 228 folk specific taxa were recorded at Tamandaré Beach; while 80, 43, and 184 were recorded at Batoque Beach, respectively. We identified five types of correspondence between scientific taxa and folk specific taxa, as well as four classification systems: hierarchical, sequential, ecological, and sociocultural. Information concerning the richness, diversity, and bioecology of fish can be obtained from the ethnobiological and ethnotaxonomic systems from fishermen along with related sociocultural parameters, such as habitat, food and fish seasonality, and the different ways of using this resource. Findings of this work will be useful in implementing proactive conservation and management plans.