Palatability of Amino Acids Isomers for Cichlid Fishes (Cichlidae)

The palatability of L-α- and D-α-isomers of alanine, aspartic and glutamic acids, and tryptophan, as well as L-α- and L-β-isomers of alanine for the Mozambique and Nile tilapias (Oreochromis mossambicus and O. niloticus, respectively), golden mbuna Melanochromis auratus, lemon cichlid Neolamprologus leleupi, and the tailbar cichlid Vieja hartwegi has been compared. Consumption of agar-agar pellets with L-α- and D‑α-isomers of aspartic and glutamic acids and tryptophan differs in Mozambique tilapia and tailbar cichlid, pellets with alanine and tryptophan, in golden mbuna, with aspartic acid and tryptophan, in lemon cichlid, and with aspartic acid, in Nile tilapia. The palatability of L-α- and L-β-isomers of alanine is significantly different for the Mozambique tilapia, lemon cichlid and tailbar cichlid. The feeding behavior exhibited by cichlids during orosensory testing of pellets is similar and little depends on the palatability of the pellets. All cichlids make a small number of rejections and repeated grasps of pellets; most cichlids retain pellets in the oral cavity many times longer in experiments that ended by consumption. The different taste properties of optical and structural isomers of amino acids for the studied cichlids confirm the species specificity of taste preferences in fish and indicate the importance of these substances as chemical regulators of trophic relationships in aquatic communities.