Abstract
The sources of variations in the weight-length relationship parameters, and in the Fulton's, allometric, and relative condition factors (K) of the characiform fish Triportheus guentheri were investigated. The use of these indices as indicators of condition were also discussed. The 2899 females and 2491 males were captured with gill nets from January 1986 to March 1988 in Tres Marias Reservoir (18° 15′ and 45° 15′ W), Brazil. Weight-length relationship parameters varied monthly in both sexes mainly due to the skewness of the relative frequency of the number of fish per body length. This suggests that a selective sample and/or the population length structure may strongly influence the estimate of those parameters. The K showed high correlations (r ≥ 0.99) among themselves. Their variations were ascribed to carcass weight in both sexes when analyzed by month, or to the ovary weights when analyzed by female gonad development intervals. The monthly weight-length relationship parameters of T. guentheri presented low or null correlation with K, except for the female's coefficient of regression. Problems using these parameters as indicators of condition suggested that they are not good indices to express condition. Some restrictions regarding the use of K are discussed.
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