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 through the pharyngeal cavity, and swallowing. Food balls with or without a feeding stimulant were inhaled with equal frequency; thus, vision was clearly the major sense affecting inhalation. However, food balls with defined concentrations 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 observations of feeding behavior suggested that both food processing and gustation occur in the pharynx and take place before the swallowing of either goldfish or food balls. The well-developed pharyngeal jaws of largemouth bass consist of six major pads of caniform teeth in the upper pharynx and two pads 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 flattened taste buds occur with the teeth. The morphology of these taste buds was typical of that described in other teleosts. Neuronal profiles, visualized with an HNK-1 monoclonal antibody, were observed entering each taste bud. The 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 receptor area. The co-localization of teeth and taste buds on the pharyngeal jaws indicates that food processing and gustation both occur there, and that together these processes determine whether a potential food item is swallowed.