The influence of odor stimulation with solutions of the amino acids L-glutamine and L-phenylalanine on the response of the cave fish Astyanax fasciatus (blind form) to the taste of agar pellets with L-glutamine and L-phenylalanine has been studied. It has been established that the odors used cause a food search behavior in fish, but do not affect the orosensory testing of the pellets. It is noted that the taste characteristics of both amino acids differ in the evaluation of the extraoral and oral taste systems, which indicates food selectivity in the blind cave fish, the food of which in its habitats is extremely monotonous. The attitude to the taste of amino acids is stable with a different smell background and a changing combination of odor and taste stimuli.

The paper reports the study of the food searching behavior in the Nile tilapia Oreochromis niloticus before and after the experimental anosmia combined with visual deprivation. The threshold concentration of the water extract of the common food organisms (Chironomidae larvae) was found for the tilapia with intact olfaction to be 10 –4 g/L, which allows this fish to search for food under the restriction of visual reception. The food searching behavior in response to food odors is completely lost as a result of irreversible anosmia and do not be restored after a 4.5-month period even for the high concentrations of the extract (10 –1 –10 –2 g/L). These findings point to the absence of external taste buds on the head, body, and fins, or to their extremely low numbers. It is assumed that tactile sense also plays a significant role in the food search and prey location in the Nile tilapia.

Food searching behavior of the Buenos Aires tetra Hyphessobrycon anisitsi has been investigated before and after experimentally induced anosmia combined with visual deprivation. The threshold concentration of a water extract of familiar food (chironomid larvae) for fish with intact olfaction was 10–6 g/L. Induced anosmia led to complete loss of the search reaction to food odor. The chemosensory behavioral response to the water extract of food used at high concentrations (10-1-10-2 g/L) was not restored in fish after 1.5, 5, or 13.5 months of anosmia. The obtained results show that the external sense of taste is absent or extremely poorly developed in the Buenos Aires tetra.

The effect of feeding and defensive motivations evoked by natural olfactory signals (food odor, alarm pheromone) on the choice and consumption of food items of different colors and tastes were examined in fish (koi Cyprinus carpio, roach Rutilus rutilus). Agar-agar pellets of red and green color containing one of the amino acids (glycine, L-proline, L-alanine; in the concentration of 0.1 M) were simultaneously given to single fish in pure water or in water extract of Chironomidae larvae or in water extract of fish skin. It was found that odors have different effects on the food-searching activity and food selectivity in fish. On the background of food odor, fish grasp pellets more often than in pure water. The equal choice of red and green pellets in pure water changes to a preference for red ones in the presence of food odor. Despite an increase in the absolute number of grasped pellets, their relative consumption is reduced and is replaced by a selective consumption of pellets with glycine regardless of their color. The increasing demand for food quality due to increased feeding motivation in response to food odor is an important adaptation enhancing the mechanisms of food selection and consumption. The defensive motivation caused by the alarm pheromone suppresses the feeding activity of fish. Fish grasp pellets several times less often than in pure water and reject most of them. There are no changes in color or taste preferences. The feeding behavior of both species is characterized by manipulation activity; it is higher in the cases of fish stimulation by food odor and when the pellet was finally rejected.

It was shown for the first time that the perception of the blind Mexican cavefish Astyanax fasciatus of the odour of food and targeted food search in response to it is completely controlled by olfaction. Blockage of olfactory reception deprives the fish of this ability. The odour concentration threshold (water extract of chironomid larvae) is 10–5 g/L. It is suggested that degeneration of visual organs does not intensify olfaction in troglobiont cavefish, but can cause its insignificant correction. Chronic anosmia (4 months) leads to weak recovery of chemoorientation, which supports the possession of external taste reception in blind cavefish.

Comparative study of the feeding behavior and gustatory preferences mediated by extraoral and intraoral gustatory reception in the stone loach Barbatula barbatula in the norm and 1–6 months after extirpation of all three pairs of barbels was performed. It was found that partial loss of external gustatory receptors and the sensory deficit caused by it do not lead to any noticeable disturbances of the ability of fish to evaluate taste properties of food objects (artificial agar-agar pellets containing L-isomers of alanine, lysine, cysteine or an water extract of chironomid larvae) and make an adequate decision of their grasping or ignoring and swallowing or refusing. The extirpation of the barbels does not influence feeding behavior related to determination by fish of the taste properties of pellets and completely retains in its ritual an obligatory preliminary examination of the food object using external gustatory reception. It is suggested that external taste buds having different localization are equally capable of providing for fish a preliminary evaluation of the taste properties of the object. After extirpation of the barbels, the efficiency of grasping pellets decreases in fish, which indicates an important role of tactile reception in the determination of the site of location of the food object and in providing of the accuracy of the hunter’s dart in fish with a weak vision development.

Feeding behavior caused by solutions of food extract (chironomid larvae, 10−2–10−4 g/l) and some free amino acids (L-proline, L-alanine, glycine, L-glutamine, L-cysteine, L-lysine; 10−4–10−5 M) in enucleated bitterling Rhodeus sericeus amarus with an intact sense of olfaction and after prolonged anosmia (6.5 months) was studied. A detailed description of feeding behavior in fish in the norm is provided, and the duration of the postoperative restoration of feeding and feeding behavior and specific features of its manifestation in enucleated and anosmiated fish are assessed. It was found that chronically anosmiated individuals of the bitterling exhibit a stereotype search behavior to solutions of food extract and several amino acids; however, the threshold concentration for these fish is higher by two orders than for fish with an intact olfaction. It is concluded that the presence in fish of external taste buds is an essential and sufficient condition for the development of compensatory processes on the external gustatory system and restoration of response to food odors after chronic anosmia. The width of the zone of distribution of taste buds on the body of fish and/or their density per unit of surface are not factors limiting the development of the compensatory process.

It was shown that stimulation by food odor (aquatic extract of food organisms, 10−2 and 10−3 g/l) does not cause shifts in gustatory preferences in carp Cyprinus carpio and cod Gadus morhua but modifies gustatory behavior. The level of consumption by carp of control granules and granules with attractive, by taste, L-proline (0.1 M) or deterrent L-lysine (0.1 M) (item by item presentation of granules) and by cod of control granules and granules with indifferent, to it, L-asparagine (0.1 M) (presentation of 10 granules simultaneously) is similar prior to and during olfactory stimulation. In the presence of food odor, the duration of taste testing for most types of granules, as well as the number of repeated graspings of granules with an attractive taste do not change in fish. At the same time, granules with indifferent or repulsive gustatory properties are rejected and repeatedly grasped by fish against the background of food odor more frequently than in water without odor. Olfactory stimulation leads to a considerable increase in the average number of graspings per one grasped granule with an indifferent or repulsive taste. Such behavior manifested by fish in the presence of food odor in response to granules with unattractive gustatory properties is apparently caused by the contradiction between the information coming via different chemosensory canals—olfactory and gustatory. The obtained results indicate that food stimulation caused by food odor in nature can lead to an increase in the actual consumption of only those accessible food items that have an attractive taste for fish.