Abstract
1. Electrical responses of the taste receptors of the lips in sea catfish (Plotosus anguillaris (LACÉPÈDE)) to various taste stimuli were studied by recording from single facial nerve fibers.
2. In addition to tactile fibers, the facial nerve innervating the barbels contains fibers which respond specifically to passive bending of the barbels. The extremely high sensitivities of barbels and lips to mechanical stimuli and the bilaterally symmetrical innervation of the facial nerve branches suggest that the tactile and the above-mentioned pressure receptors may subserve rheotropic orientation of this fish.
3. Study of single taste fiber responses showed that taste receptors of this fish could respond to NaCl, quinine and acid dissolved in seawater. Many of these single fibers responded to more than one kind of taste stimulus, but in different degrees showed a variety of individual responses. Sucrose did not produce any appreciable response in the fish tested. The stimulation effectiveness of distilled water was rather inconspicuous. We noticed highly specific responses to NaCl and to acid.
4. A fiber which responds strongly to extract of marine worm was frequently found. This fiber was commonly stimulated by blood sera of other animals and sometimes by human saliva, milk, lecithin and betaine. It seems probable that sea catfish may have highly specialized taste receptors responding to gustatory-attractive substances.
