Gustatory sensitivity of the external taste buds of Oreochromis niloticus L. to amino acids

The gustatory sensitivity of the Nile tilapia, Oreochromis niloticus L., to different amino acids was studied using an electrophysiological approach. The electrical responses were recorded from a branch of the facial nerve in nervating the external taste buds of the upper lip. The relative stimulator y effectiveness (RSE) of nine amino acids and betaine were determined at a concentration of 1 mM and all of them elicited neural responses. This speci es responded well to the neutral, basic and acidic amino acids. The most st imulatory amino acids were L-histidine, L-arginine, L-serine, L-methionine and L-glutamine; L-proline and betaine were the least stimulatory, The resu lts of this study suggest that the Nile tilapia has high external gustatory sensitivity to some amino acids as a physiological adaptation to search ef fectively for their sources, The effect of the pH, ranging from 4.0 to 9.0, on the RSE of three neutral amino acids and artificial pond water (APW) wa s also studied. The RSE increased below pH 6.0 and was relatively unaffecte d from 7.0 to 9.0, indicating that acidified stimulants are highly stimulat ory in this species. Nile tilapia did not discriminate the pH of APW as eff ectively as some of the species studied earlier.