An improved procedure to assess fish condition on the basis of length-weight relationships

Abstract

In a recent article, a new factor has been proposed to assess condition in fish (Jones et al. 1999). It is based not only on body mass and length, but also on body height. The new factor, B (= M/(L 2 × H); M, L and H = body mass, length and height, respectively), was tested against the traditional factor of Fulton, (K = M/L 3 ) using data sets for two salmonid species, and it was found to be a better pred'ictor of body mass from body dimensions. B assumes that body thickness is better correlated with length than height. To test this, we compared K and B, as well as K' (= M/L b ; b derived from regression of Log[M] against Log[L]) and B' (= M/(L × H 2 )), using data on milkfish, Chanos chanos. The factor B' consistently gave the best results, and in larger fish K'was found to be a better predictor of body mass than B. Regression analysis of body mass and height on length showed that body thickness varies isometrically with height but allometrically with length, explaining why B' is better than B.