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Fish come in many shapes, colors and sizes. There are thought to be over 20,000 species of marine fish. But all bony fish (fish that have a bony skeleton, as opposed to sharks and rays, whose skeleton is made of cartilage) have the same basic body plan.
In general, fish have the same vertebrate body as all vertebrates. This includes a notochord, head, tail, and rudimentary vertebrae. Most often, the fish body is fusiform, so it is fast-moving, but it can also be known as filiform (or eel-shaped) and vermiform (or worm-shaped). Fish are either depressed and flat or compressed to be laterally thin.
Fish Anatomy Explained
Fins: Fish have several types of fins, and they may have stiff rays in them to keep them upright. Here are the types of fish fins and where they are located:
- Dorsal fin: This fin is on the fish's back.
- Anal fin: This fin is located near the tail, on the underside of the fish.
- Pectoral fins: This fin is on each side of the fish, near its head.
- Pelvic fins: This fin is found on each side of the fish, on the underside near its head.
- Caudal fin: This is the tail.
Depending on where they are located, a fish's fins may be used for stability and hydrodynamics (e.g., the dorsal fin and anal fin), propulsion (e.g., caudal fin), or steering with occasional propulsion (e.g., the pectoral fins).
Gills: Fish have gills for breathing. This involves inhaling water through its mouth and then closing the mouth, forcing water over the gills where hemoglobin in the blood circulating in the gills absorbs dissolved oxygen in the water. The gills have a gill cover, or operculum, through which the water flows out.
Scales: Most fish have scales covered with a slimy mucus that helps protect them. There are different scale types:
- Ctenoid scales have a rough, comb-like edge
- Cycloid scales, which have a smooth edge
- Ganoid scales are thick and made of bone covered with an enamel-like substance
- Placoid scales, which are like modified teeth and give the skin of elasmobranchs a rough feel.
Lateral Line System: Some fish have a lateral line system, which is a series of sensory cells that detect water currents and depth changes. In some fish, this lateral line is visible as a line that runs from behind the fish's gills to its tail.
Swim Bladder: Many fish have a swim bladder, which is used for buoyancy. The swim bladder is a sac filled with gas that is located inside the fish. The fish can inflate or deflate the swim bladder so that it is neutrally buoyant in the water, allowing it to be at the optimal water depth.