Functional significance of the co-localization of taste buds and teeth in the pharyngeal jaws of the largemouth bass, Micropterus salmoides

Studies of feeding behavior in the largemouth bass, Micropterus salmoides, revealed that live goldfish or artificial food balls are ingested in three discrete steps: inhalation of the food into the oral cavity, passage throug h the pharyngeal cavity, and swallowing. Food balls with or without a feedi ng stimulant were inhaled with equal frequency; thus, vision was clearly th e major sense affecting inhalation. However, food balls with defined concen trations of a feeding stimulant were swallowed in a dose-dependent manner, whereas food balls without a feeding stimulant were promptly expelled. Thus , gustation played a major role in stimulating swallowing. Videotaped obser vations of feeding behavior suggested that both food processing and gustati on occur in the pharynx and take place before the swallowing of either gold fish or food balls. The well-developed pharyngeal jaws of largemouth bass c onsist of six major pads of caniform teeth in the upper pharynx and two pad s in the lower pharynx. Scanning electron microscopy showed that taste buds were abundant around most of these pharyngeal teeth. Histological sections prepared from all pharyngeal pads revealed that both elevated and flattene d taste buds occur with the teeth. The morphology of these taste buds was t ypical of that described in other teleosts. Neuronal profiles, visualized w ith an HNK-1 monoclonal antibody, were observed entering each taste bud. Th e antibody also selectively stained a group of one to four putative sensory cells in each taste bud and the distal processes of these cells in the rec eptor area. The colocalization of teeth and taste buds on the pharyngeal ja ws indicates that food processing and gustation both occur there, and that together these processes determine whether a potential food item is swallow ed.