The teleost fish, blue gourami Trichopodus trichopterus, distinguishes the taste of chemically similar substances.

Behavioural approaches permit studies of the functional features of animal gustatory systems at the organism level, but they are seldom used compared to molecular and electrophysiological methods. This imbalance is particularly apparent in studies on fish gustation. Consequently, our notion of taste preferences remains limited in fish, the most numerous and diverse group of vertebrates. The present study aimed to determine whether fish could distinguish the tastes of chemical substances with similar structures and configurations. We performed behavioural trials, where each test substance (L-alanine, glycine, L-cysteine and 9 of their derivatives; 0.1 M) was incorporated into agar pellets, and presented to blue gourami (Trichopodus trichopterus). We found that L-α-, L-β-, and D-α-alanine as well as L-cysteine and L-cystine had different palatabilities; and glycine, methyl-glycine, dimethyl-glycine-HCl, trimethyl-glycine, and glycyl-glycine had similar taste qualities. Results show that molecular transformation could shift the palatability of amino acids, which led to changes in the orosensory behaviour of blue gourami. The ability of fish to display different taste preferences for substances, like amino acids and their, derivetives, widely distributed among aquatic organisms, undoubtedly forms the sensory basis for selective feeding, which in turn, reduces the competition for food among sympatric species in natural waters.