AGOSTINHO, Angelo Antonio; MATSUURA, Yasunobu; OKADA, Edson Kiyoshi; NAKATANI, Keshiyu. The catfish, Rhinelepis aspera (Teleostei; Loricariidae), in the Guaira region of the Paraná River: an example of population estimation from catch-effort and tagging data when emigration and immigration are high. Fisheries Research, Amsterdam, v.23, no.3-4, p.333-344, 1995.Using the Leslie model, an estimate was made of the stock of the loricariid catfish, Rhinelepis aspera, in the fishing grounds in the Guaíra region of the Paraná River. The method was based on catch-effort and mark-recapture data collected over a 90 day period in 1986. The estimated initial population size, based on catch-effort, was 734 806 catfish with a biomass of 580 297 kg. During the experiment 2.372 million cattish entered the fishing area and 1.892 million catfish emigrated from it. A Petersen type estimate, based on the recapture ratio of tagged fish, was 812 359 catfish at the beginning of the experiment.