Determinação de idade em bagres da Amazônia através de anéis etários em esporões

Abstract

The number and periodicity of age rings on the spurs of two catfish species, Brachyplatystoma flavicans and B. vaillantii, are being investigated. These species are relevant for the Amazonian fishing economy, as they are the most important in the export trade of the region. Based on the methodology already existing in the literature, easily available equipment and resins were adapted to obtain the spurge cuts. The fish samples are obtained from the fishing industries in Belém and from the unloading points of the artisanal fishery, where after the forcal length measurements are taken, the dorsal fin and pectoral fin spurs are extracted. After being cleaned, the spurs are placed in acrylic resin and cut with a manual electric saw. The cuts are roughened with water sandpaper and then mounted on a slide with Canada balsam. From February 1995 to August 1995, 142 pyramutabas and 135 douradas were examined. The clearest rings were observed on the dorsal spur of the pyramutaba and less evident, but still possible to be counted, on the pectoral spurs. Curiously, the gilthead bream has a practically hollow dorsal spur, the first rings being eliminated by the expansion of the internal space; and the pectoral spurs have unclear rings, making it difficult to distinguish false from true rings. The method of age determination by counting rings on spurs has proven adequate for piramutaba. However, the same is not true for the gilthead bream, due to its hollow rings, and the analysis of other rigid structures such as vertebrae and opercula should be sought in order to study the growth of this species.