"WHAT'S ON THE OUTSIDE"
Vertebrates- animals with backbones
The external anatomy of a fish is very different from our own, because fishes are adapted to move and live in water, and we are adapted to live on land. Therefore, locomotion and sensory structures may look very different, although their general functions are very similar. For example, fishes have "noses" (called nares) that don't look anything like our own, yet their purpose is to smell chemicals in the water. Likewise, the internal anatomy will look very different from our own, however, most of the major organs are the same (e.g., heart, stomach, liver, spleen) and have the same basic function. A few internal structures, like the swim bladder, are of course unique to fishes. In this lesson we will be examining the external and internal anatomy of a bony fish and comparing this to a human.
Fishes do have a few specialized structures that have no counterpart to humans. The lateral line is one example. The lateral line detects physical vibrations in the water that allows the fish to sense other animals and objects in the water, even if they can't be seen. Many types of fishes use inner ear stones, called otoliths, to detect changes in body position. Because of their unique characteristics and growth patterns, scientists often use otoliths to classify fish, as well as determine their age. These stones rest on a bed of sensory hairs, that send messages to the brain about the orientation of the fish. Sharks have an organ in their snout, called the ampullae of Lorenzini, that detects weak electric fields. It is thought that they use this structure to detect prey, perhaps being able to distinguish the weak electrical signals given off by injured animals.