Anatomy of finfish and shellfish

Unit – 3 Study of oral region and Associated structures

3.3.1. Modifications in the shape of mouth
Among the grazers and suctorial feeders, there exist not only specially developed lips but also adaptations of other mouth parts. The Trumpet fishes (Aulostomidae) the cornet fishes (Fistularidae) and the pipe fishes (syngnanthidae) as well as many butterfly fishes (chaetodontidae) of coral reefs, have mouths that resemble elongated beaks. This adaptation is achieved by a protraction of the hyomandibular bone rather than by a lengthening of the lower jaw bones (denteries) themselves.
Among these fishes, the method of feeding may be by suction as in the case of trumpet fishes, cornet fishes and pipe fishes or it may be a selective grazing action with sharp teeth when the long snout enables the butterfly fish to reach into small crevices of the coral.
A peculiar structure among mouth modification has arisen in the half beaks (Hemiramphidae) where the lower jaw projects into a beak often a third of the length of the fish itself, with the mouth opening above it. Half beaks are usually surface feeding fishes.