Orosensory Food Testing in Fish: Chronology of Behavior.

The orosensory food testing behavior in fish was studied using the nine-spined stickleback Pungitiuspungitius as an example. The patterns of the chronology of manipulations performed by fish in testing food objects were identified. The existence of two stereotypical patterns of feeding behavior was confirmed, and their new characteristics were obtained. The relationship between the responsiveness to food and the predisposition of fish to feeding was revealed.

[TASTE ATTRACTIVENESS OF FREE AMINO ACIDS AND THEIR PHYSICOCHEMICAL AND BIOLOGICAL CHARACTERISTICS (AS EXEMPLIFIED BY FISHES)].

Using fishes as an example (32 species, II families) the relationship between taste attractiveness of free amino acids (L-isomers) and their physicochemical and biological properties was analyzed. It is shown that the essential amino acids, which are of the highest nutritional requirement for an organism, have lower taste attractiveness in fishes than nonessential ones. Only in 6 species of 32 investigated ones (sun- bleak Leucaspius delineatus, European minnow Phoxinus phoxinus, dace Leuciscus leuciscus, chub Leu- ciscus cephalus, blue gourami Trichopodus trichopterus, pearl gourami Trichopodus leerii) the relation- ship between taste preference and molecular weight of amino acids was confirmed statistically, in all cases being negative. Only in 2 species a statically significant correlation between taste properties of amino acids and the dissociation constant (K1) was found (positive in stone loach Barbatula barbatula and negative in lake charr Salvelinus namaycush). A positive correlation between taste preference and the value of isoelectric point (pI) of amino acids was found in one species (roach Rutilus rutilus) and negative correlation - in 2 species (brown trout Salmo trutta, Arctic char Salvelinus alpinus erythrinus). A significant correlation between taste attractiveness and solubility of amino acids in water.was found in 2 species (chum salmon Oncorhynchus keta and navaga Eleginus nawaga), negative in both cases. Acidic and polar uncharged amino acids more often possess flavor that stimulates food consumption than basic and non-polar ones, L-isomers of amino acids than D-isomers, amino acids with an amino group in cc-position than in ß-position. Amino acids are more attractive than their salts. Aromatic amino acids possess attrac- tive taste much less than sulfur-containing or acyclic ones. Thus, in the majority of fish species the relationship between taste attractiveness of free amino acids and many of their physical, chemical and biolo- gical properties is absent or low, indicating their indirect nature and difficulty of revealing these relation- ships.

[Selective feeding in fish: Effect of feeding and defensive motivations evoked by natural odors].

The effect of feeding and defensive motivations evoked by natural olfactory signals (the food odor, the alarm pheromone) on choice and consumption of food items different in color and taste, and the manifestation of foraging behavior were examined in fish (koi Cyprinus carpio, roach Rutilus rutilus). The agar-agar pellets of red and green color having one of the amino acids (glycine, L-proline, L-alanine; all in concentration of 0.1 M) were simultaneously offered to single fishes in pure water, and in water extract of Chironomidae larvae or in water extract of fish skin. It was found out that odors used have different effects on fish foraging activity and on pellet selection for both pellet choice and consumption. On background of food odor, fish grasped pellets more often than in pure water. The equal choice of red and green pellets in pure water shifted to the preference of red ones in the presence of food odor. Despite the increase in the absolute number of pellets grasped, the relative consumption reduced and was replaced by selective consumption of pellets with glycine regardless of their color. Increasing demand for the food quality, due to the increased feeding motivation in response to food odor, is an important adaptation enhancing selection and consumption of food with more appropriate sensory qualities for fish. Defensive motivation caused by alarm pheromone suppressed predisposition. of fish to feed. Fish grasped pellets several times less often than in pure water and refused most of them. Any changes in the color or taste preferences were absent. Feeding behavior of fish of both species was characterized by repeated intraoral pellet testing, but in koi handling was less typical than in roach. In both species, handling activity was higher in those cases when the pellet was finally rejected. This activity was enhanced also on the background of food odor.