| ¡ | Fish have been around longer than dinosaurs, approximately 500 million years |
| ¡ | All fish are vertebrates. This means they have backbones like humans and other animals most of us are familiar with. |
| ¡ | There are two main groups of fish: cartilaginous fishes, and bony fishes. Lamprey, Hagfish, sharks, skates, and rays belong to the cartilaginous fishes. Tuna, carp, salmon, bass, bluegill, and many others belong to the group of bony fishes. The backbone and skeleton of cartilaginous fish is, as the name implies, made of cartilage and is softer than that of the bony fishes. |
| ¡ | Fish are poikilothermic or "cold-blooded" meaning that they do not generate their own body temperatures as mammals do. Unlike humans for example, a fish's body temperature is very much affected by the temperature of its surroundings. |
| ¡ | Today there are approximately 25,000 known species of fish. 20,000 of those are the bony fishes. |
| Anatomy Body plan: Most fish have a fusiform body shape which just means that their bodies taper at both ends. This helps the fish to move through water more easily. In addition to the fusiform body plan, most fish are covered with a series of overlapping scales arranged in such a way that allows water to flow over them easily. As a fish moves, water flows over the scales much like rain pouring over roof shingles. Most fish also have fins on all sides of their bodies, dorsal (top), pectoral (side), pelvic or anal (bottom), and caudal (rear). Fins are are used for propulsion and stability while swimming. They are typically a thin membrane of skin supported by a series of bony ribs that are controlled by a complex series of muscles. This allows the fish to move its fins both forcefully, and delicately depending on the need. |
| Basic External Fish Anatomy |
| Breathing: Fish need oxygen just like humans. But, since most do not have lungs or breath air, they must get oxygen another way. Waters that fish live in contain dissolved oxygen and fish exrtract this oxygen with their gills. Simply put, gills are a series of delicate vascular tissues that water is pushed over. As oxygenated water comes into contact with the gills, the oxygen is absorbed by the gills and deliver it to the bloodstream. To breath, fish suck in water through the mouth and force it out through channels that pass over their gills. The gills are located in the rear jaw area of the fish and are enclosed behind an operculum. The operculum is a specialized region on the fish's head that forms a slit which can be sealed for intake of water, or unsealed to allow water to be expelled. |
| Seeing: Most fish have eyes on opposite sides of their head and can see in both directions simultaneously, unlike humans that see in only one direction and must turn their heads to see left and right. Except in sharks, fish lack eyelids. Since fish live under water there is no need to blink to keep their eyes moist. |
| Hearing: Fish have no external eardrum. They do however have an inner ear which is sensitive to sound vibrations. Sound vibrations travel through the fishes body to reach a very sensitive inner ear. Thus, fish are extremely sensitive to sound, despite not having an outer ear. |
| Touch: Fish have a strong sense of touch. Their skin is equipped with many nerve cells that detect changes in water pressures around them. They also have a unique system of channels under the skin which is connected to the lateral line system. The lateral line system runs the length of their bodies from head to tail roughly. This sensory system makes fish highly sensitive to other fish around them also. If you have ever seen large schools of fish that seem to be swimming in synchrony, it is partly because of this keen sense of touch. |
| Smell: Fish have a strong sense of smell. Two nostrils located on of the head area, between the eyes and mouth, allow water to flow in past two olfactory sense organs. |
