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Fishing tip: Light bends when it passes from air to water. The greater the angle at which light enters the water, the more it bends. Because of this, a fi sh sees objects straight overhead in their true locations, but the images of objects near the horizon are shifted. Light from an object that is on the horizon doesn't penetrate the water, so sitting while fi shing at the water's edge can help you avoid being spotted by your target. Ears Fish have internal ears. They don't need an external opening because sound travels so well through water, however the structure of a fi sh's inner ear is similar to a human's. Bony structures called otoliths make up part of the structure of the inner ear and help a fi sh to maintain its orientation and balance in the water. Like scales, otoliths can be used to determine a fi sh's age. Nares Instead of a nose, fi sh have nares on their heads. Water constantly moves through the nares, and fi sh can detect odors with them. Unlike the function of a nose, fi sh do not breathe through nares. Coloration Marine fi sh are known for having bright colors and bizarre patterns, but even freshwater fi sh have many colors and patterns. Fish that have vertical stripes often spend much of their time in aquatic vegetation, and the striped pattern on their bodies helps to camoufl age them, either to hide from predators or to lie in wait for prey. Fish with spots or blotches can blend in to a rocky or gravelly substrate. Light-colored, silvery fi sh are camoufl aged in clear, open water. Countershading, dark colors on top and light on bottom, helps fi sh to blend into their surroundings. The light bellies of many fi sh make them diffi cult to see from below because they blend in with the light coming from the sky. Likewise, the dark backs of many fi sh make them diffi cult to see from above because they blend in with the depths of the water where light doesn't penetrate. SO, WHAT IS A FISH? What are some exceptions to this list of things that make fi sh unique? ● Channel catfi sh don't have scales. ● Not all fi sh have swim bladders. Sharks don't, and neither do paddlefi sh, a fi sh found in the Missouri River. ● All fi sh live in water, but some fi sh can actually stay alive out of water for a period of time. The lungfi sh, which lives in parts of the world where there are dry seasons, can burrow into the mud when the water disappears. The fi sh remains inactive until the water comes back. ● All fi sh have fi ns, but some fi sh have fi ns that are adapted to very specifi c environments and they don't even look like fi ns. The lungfi sh is a good example of this. Its fi ns look like legs. ● Fish use gills to get oxygen from the water, but some fi sh, like gar, can use their swim bladders to get oxygen from the air. These fi sh can be observed snapping at the surface of the water to gulp air into their swim bladders. So, not all fi sh have all of these characteristics, and some things that aren't fi sh have some of these characteristics. Snakes have scales, whales are aquatic, salamanders have gills, frogs are cold blooded. Sometimes the defi nition can get a little sticky! But a good general guideline is that fi sh are cold- blooded, aquatic, they use gills to obtain oxygen, they have fi ns and scales, a slime coat and a lateral line. Fish are fi sh because they are adapted to living in a world of water. C. IVERSON, MINNESOTA DEPARTMENT OF NATURAL RESOURCES 37 CHAPTER 6 ● FISH ANATOMY