THE CATFISH, RHINELEPIS-ASPERA (TELEOSTEI LORICARIIDAE), IN THE GUAIRA REGION OF THE PARANA RIVER - AN EXAMPLE OF POPULATION ESTIMATION FROM CATCH-EFFORT AND TAGGING DATA WHEN EMIGRATION AND IMMIGRATION ARE HIGH

Using the Leslie model, an estimate was made of the stock of the loric ariid catfish, Rhinelepis aspera, in the fishing grounds in the Guaira region of the Parana River. The method was based on catch-effort and mark-recapture-data collected over a 90 day period in 1986. The estima ted initial population size, based on catch-effort, was 734 806 catfis h with a biomass of 580 297 kg. During the experiment 2.372 million ca tfish entered the fishing area and 1.892 million catfish emigrated fro m it. A Petersen type estimate, based on the recapture ratio of tagged fish, was 812 359 catfish at the beginning of the experiment.