POST-LARVAL DEVELOPMENT OF THE MASTICATING APPARATUS OF BLACK CARP MYLOPHARYNGODON PICEUS(RICHARDSON)

The masticating apparatus (the pharyngeal teeth and the horny pad) of black carp is formed gradually during postlarval development. The pharyngeal teeth grow on the pharyngeal bones on the bottom of the posterior pharyngeal cavity, while the horny pad is situated on the roof of the cavity, opposite to the pharyngeal teeth. The development of the pharyngeal teeth can be divided into three stages, i.e., original teeth, transitional teeth and fixed teeth. The original teeth have only one generation, with a dental formula of 1,2/2,1. The transitional teeth have three generations, and the dental formulae are 3/3, 4/4 and 4/5 respectively. The fixed teeth have several generations. During the first year, there are two to three generations with a dental formula of 4/5. The pharyngeal teeth are changed several times in the life-cycle. During the first year, the old teeth are displaced by the new ones repeatedly (five to six times). In each generation, the rate of change is higher in the earlier stage than in the latter stage. The teeth are changed one by one and alternatively from either side. When an old tooth is thin, absorbed and dropped, it is substituted by a new one. The fixed teeth have typical structures of enamel, dentine, pulp, pulp-cavity and cement. The horny pad appears later than the pharyngeal teeth and is composed of three layers: cuticle (outer layer), granular layer (middle layer) and germinal (basal) layer. The thickness and strength of the horny pad increase with the growth of the animal. The development of the masticating apparatus is closely associated with changes in the feeding habit. At the original teeth stage, the masticating apparatus is not capable of masticating food and the fish changes from heterogenous feeding to zooplankton-feeding. At the transitional stage, the apparatus has weak ability to masticate food and is not capable of grinding; the diet of the fish changes from zooplankton to benthos like chironomid larvae. At the fixed teeth stage, the apparatus is capable of masticating and grinding benthic animals with shells, i.e. snails.