Growth and replacement of teeth on jaw bones in adult amago salmon, Oncorhynchus rhodurus

Abstract

Tooth replacement in bony fishes is more complicated than postulated by the Zahnreihe concept by Edmund (1960). In this paper, the growth and replacement of teeth on the maxillary and dentary in abult amago salmon, Oncorhynchus rhodurus is described. The present study is based upon 20 male ranging from 33cm to 40cm in standard length (SL), 20 female from 25cm to 30cm SL, fully matured amago salmon, and 20 young from 5.5cm to 6.5cm SL. All of specimens were stained with alizarin red S, and upper and lower jaws of adult fish were radiographed. The position of toothgerms, functional teeth and traces of lost teeth in the tooth row on the maxillary and dentary were determined in these stained specimens.
When the toothgerm appeared at the nth-tooth position, the frequencies of the appearance of toothgerms were 20.2-20.3% at the (n+1) th tooth position, 53.8-58.7% at the (n+2) th, 19.8-20.2% at the (n+3) th and 1.6-4.3% at the (n+4) th in the tooth row on the dentary, and were 11.8-19.4% at the (n+l) th tooth position, 38.9-44.3% at the (n+2) th and 26.0-36.1% at the (n+3) th on the maxillary of the adult fish. But, in the young fish, when the toothgerm appeared at the nth-tooth position, the frequencies of appearance of toothgerms was 42.5% at the (n+1) th tooth position and 53.9% at the (n+2) th in the tooth row on the dentary, and, 41.6% at the (n+l) th and 45.5% at the (n+2) th on the maxillary. The findings on the adult amago salmon may support Osborn's hypothesis (1971), but those on the young fish may not support the hypothesis. Furthermore, the shedding of functional teeth may produce a condition which stimulates a development of the teeth around them on the dentary and maxillary in amago salmon.