SCALING OF SKELETAL MASS TO BODY-MASS IN FISHES

The few available observations are consistent with the supposition tha t 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, an d in phylogeny with adult coral reef fishes. Body mass and skeletal ma ss were measured for freshly caught fishes. Data were transformed to l ogarithms and fitted to a power function with least-square linear regr ession. 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) indic ated positive allometric scaling of the skeleton during ontogeny. The scaling pattern was isometric for a multispecies sample of perciform f ishes from coral reefs (b = 0.82; CI = 0.21). However, the single perc iform species with the largest number of individuals in the sample, Ep inephelus guttatus, was positively allometric (b = 1.13; CI = 0.12), w hereas the tetraodontiform, Balistes vetula, was isometric (b = 1.05; CI = 0.12). Instead of leading to isometry, weightlessness may increas e 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 loc omotion in water rather than be driven by the need to resist gravity. (C) 1996 Wiley-Liss, Inc.