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— Palatability of sodium cholate (10 –1 M), sodium taurocholate (10 –1 M), and dehydrocholic acid (0.5 × 10 –3 M) for Mexican cavefish Astyanax fasciatus (blind form), silver dollar Metynnis argenteus , Nile tilapia Oreochromis niloticus , green swordtail Xiphophorus hellerii , and roach Rutilus rutilus was assessed. All substances have a significant taste effect, but the reaction of fishes to their taste is different and the responses to the same substance were different. Taste attractiveness for bile substances (sodium taurocholate, dehydrocholic acid) was found only in Mexican cavefish, which allows it to feed on specific food (bat guano) available in cave reservoirs where other food resources are extremely insignificant. For the rest of the fishes, bile substances had an inert or aversive taste, which can prevent coprophagy and contribute to long-term preservation of feces in the environment, which are an important source of odor signals for fish. It has been proposed to consider bile substances as important chemical regulators of fish relationships in aquatic communities.

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.

The palatability of six species of aquatic animals and five species of plants for the Nile tilapia Oreochromis niloticus was evaluated. Aqueous extracts of most organisms (ten of 11 species) have an attractive taste, which corresponds to euryphagia and nutritional plasticity of the Nile tilapia. Despite phytophagia, the palatability of an animal extract is higher than that of plants. The low stimulating effect of the extract of the duckweed Lemna minor suggests the presence of natural taste deterrents in it. The extract of the Canadian waterweed Elodea canadensis , depending on the origin of the plant, either completely blocks consumption or has inert taste properties. Different parts of the water hyacinth Eichhornia crassipes (leaves, roots) have a similar palatability. Repeated grasps manifested during orosensory testing of food are not typical for feeding behavior of the Nile tilapia. The results of the study indicate the ability of fish to subtly differentiate food organisms according to their taste qualities and emphasize the important role of taste reception in the choice of food objects by fish.

A rapid, sensitive and precise procedure of detecting cytomegalovirus (CMV) DNA in human tissue and biological liquid by means of the thermostable DNA-polymerase from