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

Abstract

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.