Information on the Animal Class Fish
What are fish?
Characteristics and Special Features of Fish:
- Oldest vertebrates: Fish are the ancestors of all vertebrates and have existed for over 450 million years.
- Vertebrates: Fish have an internal skeleton with a spine made of bones (bony fish) or cartilage (cartilaginous fish).
- Gills for breathing: They extract oxygen from water using their gills.
- Reproduction: Most species lay eggs, referred to as spawning.
- Cold-blooded: Their body temperature adjusts to the surrounding temperature (ectothermic).
- Scales: Their skin is typically covered with protective scales.
- Swim bladder: A gas-filled organ helps many fish to float in water without sinking.
- Lateral line system: A sensory organ that allows fish to detect pressure changes and movements.
The Evolution of Fish
Fish evolved 450 million years ago and are the oldest vertebrates. There are two main types: cartilaginous fish (like sharks, rays) and bony fish (almost all others). Cartilaginous fish have a skeleton made of cartilage and their skin is covered in tiny teeth instead of scales. They do not have a swim bladder and must swim actively to maintain their position in the water).
Habitat
Where Can Fish Be Found?
Fish have a very limited habitat. They reside in:
- Freshwater
- Saltwater
- Brackish water (a mix of fresh and saltwater found in coastal areas and river mouths)
How Do Fish Differ from Other Animals?
Fish possess gills that allow them to extract oxygen from water.
Diet
What Do Fish Eat?
The diet of fish primarily consists of zooplankton (tiny organisms), other fish, crustaceans, insect larvae, worms, and spawn. Depending on the species, they can be:
- Herbivores (plant-eaters)
- Carnivores (meat-eaters/predators)
- Omnivores (eating both plants and animals)
Some fish have specialized in algae or snails.
Movement
How Do Fish Move?
Fish swim using their fins and muscles.
- Pectoral and pelvic fins: Steering rudders that help them determine direction
- Tail fin: The "engine" or propulsion for movement
- Dorsal fin: Provides stability and balance at high speeds
There are also fish that can "fly" or climb (see Fun Facts).
Reproduction
How Do Fish Reproduce?
Fish lay eggs. Most do not care for their young, meaning that the fry are on their own once they hatch. Some fish guard the eggs, and a few even give birth to live young (e.g., sharks).
Interesting Facts
Can Fish Get Seasick?
Yes! Just like humans, fish have a balance organ. When the sea is rough, they dive a bit deeper where the water is calmer. If that doesn't help and they still feel unwell, they "vomit" into the ocean (yummy!).
Do Fish Ever Get Thirsty?
With all that water around, one might wonder: Do fish need to drink? Sort of. While they don't drink like we do, fish still absorb liquid through their skin.
Are There Really Flying Fish?
Yes! However, they don't have wings and they don't sit in tiny toy airplanes (just kidding). They flap their tail fin very quickly and launch themselves upwards this way. They can soar up to 5 meters!
Are There Fish That Can Climb?
Even more impressive than flying fish are climbing fish. The mudskipper has long pectoral fins that it can use like arms. With these, it crawls up trees to catch insects.
Species
There are more than 32,500 species of fish:
| Bony fish (osteichthyes): | ca. 29,000 |
| Cartilaginous fish (chondrichthyes): | ca. 1,100 |
The most biodiverse animal orders are:
| Perciformes: | 14.400 |
| Cypriniformes: | 3,250 |
| Catfish: | 3,400 |
| Eels: | 900 |
| Flatfish: | 400 |
| Codfish: | 48 |
Biodiversity
The remora rarely swims on its own; instead, it attaches itself to other fish with a suction cup. Its "driver" benefits too: the remora eats parasites that have settled on the skin. What does this have to do with biodiversity?
Related Articles:
Recommended Videos:
Symbiotic Animal Relationships
Animal Camouflage
Animal Eating Habits
