Intestine length in the fishes of a tropical stream: 1. Ontogenetic allometry

Synopsis We examined the ontogenetic allometry of intestine length in relation to body length and body mass in 21 species of fish from forest streams in Panama. The relationships between log₁₀ intestine length and log₁₀ body length and mass were well described by linear regressions, although some species showed slight curvilinearity. Slopes and intercepts of the linear regressions varied considerably among species. Intestine length was positively allometric in most species, with slopes of the intestine length:body length relationship ranging from 1.09 to 2.11. Relative intestine lengths (intestine length/body length) varied by two orders of magnitude (0.39–38.44) in the data set as a whole, but the variation was about one order of magnitude when species were compared at a common body size. Species in which body mass increased more rapidly with body length had more rapid increases in intestine length with body length. Among omnivorous and carnivorous species compared at the same body length, heavier species had longer intestines. Interspecific comparisons of relative intestine length may produce misleading conclusions unless comparisons are made at a common size and account for differences in relative mass.