Development of a morphological index of the nutritional status of juvenile largemouth bass

We describe the morphological changes associated with starvation in larval large-mouth bass Micropterus salmoides and develop bivariate and multivariate morphological indices of nutritional status. We obtained hatchery-reared largemouth bass, raised them until completion of fin development, and divided them into two randomized experimental groups of fed and unfed fishes. Fed fishes were provided with newly hatched brine shrimp twice daily. We quantified morphological changes in body shape using 23 morphometric characters. After only 3 d of food deprivation, we were able to detect statistically significant differences in morphology between the fed and unfed fish using multivariate analysis. The magnitude of the mean difference increased over time. An unexpected result suggested that a simple, bivariate ratio of standard length to body depth at the anus was almost as efficient and robust at classifying fed and unfed largemouth bass from an independent data set as a multivariate index based on all 23 morphometric characters. The relative ease of use, combined with a small level of misclassification error rate and a firm foundation in whole-body changes, makes these ratio indices effective tools for detecting food deprivation in larval largemouth bass.