Dental Sexual Dimorphism and Food Habits in the Stingray Dasyatis akajei from Tokyo Bay, Japan.

Abstract

Dental sexual dimorphism was observed in the stingray Dasyatis akajei. There was no difference between sexes in dentition at the juvenile stage. However, mature males had a pointed cusp for each tooth while mature females had virtually flat teeth with irregular surfaces. Sexual dental dimorphism occurred between a disc width of 350 and 400mm for males collected in Tokyo Bay, Japan. This size range was almost identical to the size at maturity for males, estimated from abrupt increments in clasper length and testis weight. Food habits expressed by frequency of occurrence of prey items showed no large difference between sexes. The main food items were crustaceans and fishes. The findings suggest that sexual heterodonty is closely related to the mating behavior of male stingrays. Another form of sexual dimorphism was found in size at maturity, i.e. smaller in males than females by a disc width of approximately 200mm.