Development of the pharyngeal dentition of two herbivorous halfbeaks (Teleostei : Hemiramphidae) and implications for the hemiramphid ontogenetic trophic shift

Abstract

Development of the pharyngeal dentition of two herbivorous halfbeaks, Hyporhamphus regularis ardelio (Whitley, 1931) and Arrhamphus sclerolepis krefftii (Steindachner, 1867), was examined quantitatively to assess features that might confer their ability to shift their diet from animal to plant material. Toothed area, tooth number, maximum tooth diameter and tooth wear area in both pharyngeal tooth pads of both taxa increased with ontogeny, whereas tooth density decreased. Comparing individuals of the two taxa at similar standard lengths indicated that A. sclerolepis krefftii showed hypertrophy of the majority of pharyngeal characters in relation to H. regularis ardelio of a similar standard length. That A. sclerolepis krefftii is more developmentally advanced than H. regularis ardelio in almost all dentigerous characters studied indicates that pharyngeal development may allow the former to commence herbivory at a smaller standard length than the latter species. The evolutionary and ecological implications of these findings are discussed in the context of a group of fishes that is overexploited worldwide.