Length and coiling patterns of the gastrointestinal tract of a group of rock-dwelling
cichlid fishes (the 'mbuna') from Lake Malawi, Africa are reported in this study. In the
16 species of primarily herbivorous fish examined, diet and habitat correlated with gut
length. Species feeding primarily on diatoms in sediment-rich environments have longer
intestines than those feeding on more animal material or in sediment-free environments.
The coiling pattern of the gastrointestinal tract is equivalent for all species and does
not appear to be taxonomically useful within the group. If intestine length is responsive,
in either ecological or evolutionary time scales, to changes in diet, this permits
flexibility in the range of dietary items that a particular individual or lineage may
consume. Structural specializations, such as intestine morphology, promoting differential
resource utilization characterize the adaptive radiation of the family Cichlidae and
facilitate ecological coexistence in these high diversity assemblages.