抄録
The order and the period of formation and shedding of conical teeth on the dentary and the period of eruption of comb-like teeth on the jaw in young ayu, Plecoglossus altivelis, were described to compare with the tooth replacement patterns of other species of fishes.In 1980, about 200 juvenile and young ayu were collected from the mouth of the Yahagi River (Mikawa Bay, Aichi Pref.), and in 1981, about 260 juvenile and young ayu were collected from Lake Biwa (Kohoku-cho, Shiga Pref.).All specimens were stained with alizarin red S.
In juvenile and young ayu (35-70mm SL), conical teeth were arranged in a series on the upper edge of the dentary.The formation of small teeth on the anterior part of the dentary progressed forward and backward from both ends of small tooth rows.The formation of large teeth which were arranged at the rear of the small tooth rows progressed backward.The lengths of large teeth on the posterior part of the dentary were significantly larger than small teeth on the anterior part of the dentary.The two types of tooth rows on the dentary were recognized in young stages.The toothgerm did not appear in the small tooth rows on the dentary in specimens larger than 50 mm SL, but the toothgerm usually appeared at the end of large tooth rows until the shedding of conical teeth was completed.Furthermore, in specimens 35-50 mm SL having6-10 teeth, the toothgerms of small teeth appeared irregularly throughout the small tooth rows.Conical teeth began to shed from the dentary at the anterior part of the tooth rows in specimens 50-55 mm SL, and the shedding progressed backward along tooth rows.The shedding of small teeth was accompanied with the absorption of the part of the dentary surrounding the bases of the teeth.But large teeth were dropped at the upper edge of the dentary.The periods of eruption of comb-like teeth in young ayu basically coincided with the periods when the small teeth finished to form the toothgerms.
The present findings on the growth and replacement of dentary teeth in young ayu are not similar to the tooth replacement patterns in some species of bony fishes (Evans and Deubler, 1955;Wakita et al., 1977;Nakajima, 1979;Komada, in press) and do not support the Zahnreihe concept of Edmund (1960).
