Taste preferences, orosensory food testing, and sound production during feeding by the pearl gourami Trichopodus leerii (Osphronemidae)

Abstract

It has been found that the pearl gourami Trichopodus leerii evaluates the quality of food objects (agar–agar pellets with standard size, shape, and color but having different composition) by touching them with their lips without using its long filamentous ventral fins. Orosensory testing is accompanied by repeated grasps−rejections−grasps of the pellets (up to 28 times). Such manipulations become significantly more frequent and the pellet is retained several times longer if the trial ends with ingestion rather than final refusal of the object by the fish. It has been found for the first time that pearl gourami produces clicking sounds while grasping the pellets. The number of sounds is directly related to the number of grasps of the object performed by the fish. Only two (alanine, serine) of 21 amino acids (L-isomers) were attractive to pearl gourami, another 13 acids turned out to be indifferent stimuli, and six acids had a repulsive taste. Pearl gourami was attracted to the taste of sucrose and Chironomidae larvae extract. The addition of citric acid, calcium chloride, and sodium chloride to the pellets did not influence their consumption by the fish. The more attractive the substances contained by the pellets, the longer time is spent by the fish on orosensory testing of the pellet quality.