Scaling of skeletal mass to body mass in fishes.

Abstract

The few available observations are consistent with the supposition that the relative weightlessness of fishes leads to isometric scaling of skeletal mass to body mass. To explore further this pattern we studied scaling in ontogeny with freshwater tilapia, Oreochromis nilotica, and in phylogeny with adult coral reef fishes. Body mass and skeletal mass were measured for freshly caught fishes. Data were transformed to logarithms and fitted to a power function with least-square linear regression. Whereas slope for all O. nilotica combined was consistent with isometry (b = 1.00; 95% CI = 0.02), slopes calculated separately for juveniles (b = 1.16; CI = 0.07) and adults (b = 1.10; CI = 0.07) indicated positive allometric scaling of the skeleton during ontogeny. The scaling pattern was isometric for a multispecies sample of perciform fishes from coral reefs (b = 0.82; CI = 0.21). However, the single perciform species with the largest number of individuals in the sample, Epinephelus guttatus, was positively allometric (b = 1.13; CI = 0.12), whereas the tetraodontiform, Balistes vetula, was isometric (b = 1.05; CI = 0.12). Instead of leading to isometry, weightlessness may increase the range of possibilities for the scaling of skeleton mass to body mass in fishes compared to terrestrial vertebrates. The scaling of the skeleton in fishes may be related to foraging style and manner of locomotion in water rather than be driven by the need to resist gravity. © 1996 Wiley-Liss, Inc.