| Summary: | We investigated the relationship between fat content and condition indices in Atlantic salmon Salmo salar parr sampled from a wild population on a seasonal basis. Condition of individual fish was indexed by residuals from the least-squares regressions of fat weight, dry weight, wet weight, and water weight (separately on fork length) as well as by relative condition factor, Fulton's condition factor, percent fat, and percent water. For all fish analyzed in the study (n = 284), residualized fat weight accounted for 81% of the variation in percent fat, for 58% of the variation in residualized dry weight, for 46% of the variation in residualized wet weight and relative condition factor, for 41% of the variation in Fulton's condition factor, for 35% of the variation in residualized water weight, and for 28% of the variation in percent water. All indices except Fulton's condition factor, residualized water weight, and percent water were significantly correlated with fat weight for all combinations of sex and season. The indices based on fat weight provided the most information about seasonal and gender differences in terms of nutritional status, followed by the index based on dry weight, the indices based on wet weight, and the indices based on water weight. Residual indices are useful for testing the relationship between physiological and morphometric condition indices, and they provide an alternative to more traditional condition indices when the assumptions underlying the use of traditional indices are not valid.
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