Tooth and Gut Morphology in Relation To Feeding in Three Girellid Species (Perciformes, Girellidae) From Southern Japan

Abstract

Jaw dentition, tooth replacement patterns, relative length of the intestine, intestinal coiling patterns and feeding behaviour in the natural habitat were studied in three girellid species from Japan, Girella punctata, G. melanichthys and G. mezina. They share a troughlike structure in the premaxilla and the dentary. The trough is larger and deeper in G. punctata and G. mezina than in G. melanichthys. Girella punctata and G. mezina have 2 or 3-4 rows of slender functional teeth while G. melanichthys has a single row of short and stout teeth. Tooth replacement waves proceed from mesial to distal side of the jaw on each oblique tooth row. In G. mezina, teeth at the occlusal surface are probably replaced almost simultaneously, but this does not apply to G. punctata and G. melanichthys. Differences in tooth wearing and replacement pattern among the three species suggest differences in their feeding habits. Girella melanichthys and G. punctata browse epilithic algae, especially algal fronds on the rock surface, while G. mezina grazes epilithic filamentous algae and diatoms in particular. Numerous replacement teeth in G. mezina are a possible adaptation for compensating rapid crown wear, differing in this respect from G. melanichthys with fewer replacement teeth and less rapid crown wear. In G. punctata, the replacement teeth are intermediate between the other two species. Girella mezina has a longer intestine with a more complicated coiling pattern than G. punctata and G. melanichthys, which have similar intestinal characteristics. Morphological characters and feeding observations suggest that G. mezina is a grazer, G. melanichthys a browser and G. punctata an intermediatc feeder.