Taste and Olfactory Stimuli and Behavior in Fishes

Abstract

When searching for food different fish species use the same sensory mechanisms differentially. At one extreme there are omnivorous fishes such as catfish and carp that, in addition to vision, use the taste system to excite and release reflex responses and the olfactory system to excite and discriminate chemical stimuli. On the other extreme are predatory fishes that detect prey visually and, if not conditioned differentially at fry and fingerling stages, do not use chemosensory information for food finding at all. Depending on the mechanisms that they use to detect and collect food, the fishes that have been studied to date occupy the following ecological niches. (1) Bullhead catfish (Ameiurus melas) type omnivorous niche: bullhead catfishes use chemical and tactile senses to release appetitive and consummatory phases of feeding behavior. They also detect prey by the passive electric sense. (2) Channel catfish (tctalurus punctatus) type omnivorous niche: channel catfish use vision for prédation and, in addition, chemical and tactile senses. (3) Carp (Cyprinus carpio) and goldfish (Carrasius auratus) type omnivorous niche: carp use visual and chemical senses for food collection, they have taste-controlled reflex snapping/biting mechanisms and, in addition, they use oral food sorting to separate edible from inedible objects. (4) Rainbow trout (Oncorhyncus mykiss) type visual hunters niche: farmraised rainbow trout use vision and/or olfaction to get excited and search for food. (5) Exclusively visual hunters niche: in nature, European hue hen (Hucho hucho) and walleye (Stizostedion vitreum) consume exclusively living prey such as fish and crustaceans that they locate by vision.

Physiologically functional olfactory (Cooper and Hasler, 1976; Shoji et al., 1994) and taste organs (Marui et al., 1983) do not necessarily indicate that a predatory fish uses either olfaction or taste to find food. In nature, visual hunters such as huchen and walleye do not get excited by taste and olfactory stimuli, they neither bite/snap after taste stimulation nor do they use olfaction to discriminate chemical stimuli. In most predatory fishes the taste system is used solely during oral food evaluation. At fry and early fingerling stages, huchen and walleye can learn to eat non-living foods such as minced liver and industrial starter feed. Juvenile walleye were conditioned in a first step to eat non-living food, to respond to olfactory stimuli in a second step and, in a third step, to discriminate amino acids. Thus, early learning influences the functional expression of the nerve networks that enable the use of olfactory information in the control of feeding in predatory fish.