Gross Morphology and Configuration of Digestive Tracts of Cichlidae (Teleostei, Perciformes): Phylogenetic and Functional , Significance

Abstract

The gross morphology of cichlid digestive tracts is investigated in 71 African, Neotropical and Asian species with differing food preferences and body shapes. Eight other perciform families are included for outgroup comparison. The ontogeny of the digestive tract is investigated in four cichlid species. The arrangement of the digestive tract of cichlids is unique among all fishes examined hitherto: the stomach's extendible blind pouch, the left hand exit to the anterior intestine and the first intestinal loop at the left side. This corroborates the monophyly of the family. The length of cichlid intestines and their concomitant coiling types appear to depend upon food preference: piscivorous, paedophagous and crustacean eating species have simple and short intestines, whilst phytophagous, insectivorous, detritivorous, zoo- and phytoplanktivorous forms are characterized by long intestines. The intestinal length of the different molluscivorous species examined depends on the amount of detritus in the diet. The possible adaptive significance of intestinal lengthening is discussed and three different ways of intestinal arrangement are defined. The digestive tracts of the African genera Haplochromis, Hoplotilapia, Platytaeniodus, Astatoreochromis, Macropleurodus, Pseudotropheus, Melanochromis, Cyrtocara, Petrotilapia, Au lonocara, Labeotropheus, Pelvicachromis and Sarotherodon are characterized by a typical dorsal intestinal flap-back-loop. This loop is lacking in the west African genus Hemi chromis, in all Neotropical cichlids and in all outgroup taxa examined and as such appears to be of possible phyletic significance.