3 Sensory Capabilities of Fish
Learning Objectives
- Recognize the adaptive significance of sensory capabilities of fish.
- Compare and contrast the sensory system of humans and fish.
- Relate the sensitivities of fish to the characteristics of the underwater world.
- Describe how sensory capabilities relate to the fish’s ability to communicate and orient.
- Express how the sensory abilities lead to responses to environmental stimuli.
- Apply concepts of fish sensory capabilities to predict effects of humans on fish.
3.1 Introduction
Fish may seem alien to us because they evolved in water and their senses are more adapted to an aquatic environment. Yet, like humans, fish depend on many senses for survival. Vision is a dominant sense in fish, and we humans can appreciate the capability for depth perception and color discrimination. But what happens when you attempt to see underwater? Your vision is very blurry underwater. Somehow fish solved the problem of seeing underwater. Sensory capabilities of fish are adapted to accommodate the special characteristics of the aquatic environment.
Imagine, if you will, a day in the life of a fish. Without eyelids, their eyes are open all the time. Daily cycles of light intensity are sensed by photoreceptors in the eye and pineal organ in the brain, which contains light-sensitive nerve endings. Vision is a dominant sense of fish that we humans can appreciate. Whether the fish finds a meal or becomes prey depends on many senses, such as the abilities to see, hear, smell, taste, and to detect water movement and electrical fields. Fish have a special sense that humans do not have: the ability to detect vibrations moving through water. Because sound vibrations move easily through water, fish do not need external ear openings, and yet they also have sensitive hearing.
Together, fish use these senses to inspect the world around them. Imagine an angler tossing a lure nearby. The fish will feel the vibrations caused by the waves moving from the lure. With wide-angle vision, the fish moves toward the lure to inspect it. With an acute sense of smell, it detects no signal that suggests it’s living. In some cases, the fish will grab a bait, taste it with sensitive taste buds, and reject it as nonfood. If captured, the fish has many sensory structures in the skin to detect touch and temperature changes.
But fish use sense for more than just finding food. Fish can rely on one or more sensory cues and different sensory mechanisms to gain information about their environment and guide their behavior. Senses are engaged whether the fish is moving toward a sound, away from a threat, or following a scent of food or pheromones. For example, young glass eels (Anguilla spp.) return to estuaries and detect currents using their magnetic compass to memorize magnetic direction of tidal flows (Cresci et al. 2019). As you learn more about the sensory capabilities of fish, you will be better able to understand their behavior.
3.2 Characteri