GUSTATION AND TASTE ORGAN IN THE BARBEL OF THE AFRICAN CATFISH

The maxillary barbel of the African catish,Clarias gariepinus, contains epidermalchemosensory organs, the taste buds.It was estimated that there are 12 taste buds in eachmm2 of the maxillary barbel epidennis.The gustatory sensitivity to the extracts of animal tissues and amino acids was studied by recording the neural responses from thebranch of the facial nerve innervating the maxillary barbel.Positive gustatory responses to the tested stimulatory compounds,except Glycine,L-proline,L-Tryptophan and L-Tyrosine, were observed.Among the amino acids tested, the most potent stimulus is L-Arginine which has an approximate electro-physiological threshold of 10-7 mol / L. The taste responses to amino acids and the extracts have similar characteristics,rapid adaptation,phasic response,and saturation athigh concentrations.However,the threshold,the gradient and the response magnitudefor the chemicals tested at same concentrations in the present study are different fromone stimulus to another. The more sensitive stimuli by electrophysiological recordings are also the more effective feeding-stimulatory substance. The results indicate further that the gustatory responses of the epidermal taste buds are related with the exploratory and feeding behaviorin african catfish.It is suggested that some water-Soluble amino acids in feeds may evokefeeding responses.