Dynamics of tooth formation and replacement in the zebrafish (Danio rerio) (Teleostei, Cyprinidae).

We have used three-dimensional reconstructions from serial sections as well as cleared and stained specimens to infer patterning of the pharyngeal dentition throughout ontogeny in the zebrafish. Each pharyngeal tooth has been monitored from its initiation to its complete disappearance (resorption and shedding). We have identified tooth families and have studied the persistence of the pattern through successive replacements. Teeth arise in two seemingly independent clusters, a ventral and a dorsal cluster, with differing patterning features. The ventral cluster consists of one row of five teeth in which a tooth is first initiated in position four, and subsequent teeth in adjacent positions, posterior and anterior to it. Replacement teeth in odd and even positions are initiated simultaneously during successive odontogenic waves but differ in generation number according to the timing of appearance of the first-generation tooth, i.e., the founder of the tooth family. Up to four teeth of a single tooth family are simultaneously present in early juveniles of which two are usually "co-functional." The number of teeth per tooth family is reduced in older juveniles and adults, reflecting a slowing down of the replacement rate. The consistent way in which the pattern is established and maintained during ontogeny calls for research of the presence of specific molecular controls.