Growth of the Medaka (VI) – Development of Oral Skeletons and Teeth During Metamorphosis

The present paper describes observational results on development of the oral skeletons including general features of dentition in the period of metamorphosis in the medaka, Oryzias latipes. The oral teeth develop progressively in parallel with the development of the dentigerous dentary in the lower jaw and the dentigerous premaxilla and edentulous maxilla in the upper jaw. Shortly after hatching, the first two teeth in lower jaw already bud on the ossified thin dentary. On the other hand, the first teeth in the upper jaw are observed in the larva about 6.5 mm total length (TL). Newly formed replacement teeth bud in the inside or outside of the exiting tooth row in the upper and lower jaws. The developmental process of the structural changes in oral teeth and the skeletal elements that support the dentary and premaxilla was morphometrically examined in metamorphic phases from the larval to the juvenile. The size of the skeletons and teeth increases with ossification in proportion to body growth. After hatching, the ossification process of the oral skeletons advances in the following order: the dentary, maxilla, retroarticular, palatine, quadrate, premaxilla, anguloarticular and ethmoidal bones