Determinação de idade de dourada (brachyplatystoma flavicans), através de leitura dos anéis etários em vértebras

Abstract

The sea bream (Brachyplatystoma flavicans) is a species of Siluriformes, in the family Pimelodidae, which has a wide distribution in the Amazon and Orinoco river basins and fishing importance for Brazil, Colombia and Peru. Considering that the management of fishery resources takes into account the growth of the stock, this project intends to estimate the parameters that describe its individual growth. One of the methods to study growth is by determining ages obtained from age rings on rigid body structures. The present study intends to determine the age of the gilthead sea bream by counting the rings on their vertebrae. The specimens analyzed were captured in the mouth areas of the Amazon rivers by the JICA-MPEG Project over three collection periods, dry 1996 and rainy and dry 1997. The length and weight measurements, sex and vertebrae of the larger specimens were obtained on board and those of the smaller ones in the laboratory. The vertebrae were treated and examined in the laboratory, where the measurements of total radius and radius of each ring were obtained. No significant difference was found between the parameters of weight and length ratios between the sexes, and the expression that defines this ratio for both sexes is: 6.83.10 -6. . Length 30755 (n=668,P >0.01 r=0.99). The relationship between that of vertebra radius and fish length was first made by discriminating between sexes. Similarly to the previous relationship, no significant difference was found for both sexes. The relationship between these variables is then expressed by the following equation: Length=152.58. Radius 0.785 (n=653, P >0.01 r=0.92). Although there is a good correlation between fish length and vertebra radius the criteria for identifying rings is not yet established. The distinction between false and true rings is still not clear, and the first and last rings are difficult to visualize in larger individuals. Only if this criterion is established will we be able to estimate the age of Dourada.