Info on the Animal Class Fish

Main Characteristics of Fish:

  • Fishes are the oldest vertebrates.
  • Fishes breathe through gills.
  • Fishes lay eggs.
  • Most fishes are ectothermic.

Fishes emerged about 450 million years ago. They are the oldest vertebrates. You differentiate between cartilaginous fishes (e.g. sharks, rays) and osteichthyes (almost all other species). Cartilaginous fishes have a skeleton consisting of cartilages and their skin is made up of tiny dermal denticles instead of scales. They do not have a swim bladder and have to actively swim in order not to sink.

Where do Fishes Live?

Fishes exclusively live in waters.

How do Fishes Differ From Other Animals?

Fishes have gills to breathe in the water.

What do Fishes Eat?

Fishes feed on plankton (tiny organisms) and other marine creatures.

How do Fishes Move?

Fishes use their fins and muscles to swim. The pectoral and ventral fins help them to navigate, while the tail fin usually serves as a “engine” to move along. There are a few fishes that also can “fly” or climb (see Special Aspects).

Whale Shark Whale Shark - Photo: Dai Mar Tamarack/Shutterstock

How do Fishes Reproduce?

Fishes lay eggs. Most of them do not take care of their offspring. This means that the young have to look after themselves after they have hatched out. Some fishes guard their eggs, some of them even give birth to babies (e.g. sharks).

Special Aspects:

• Can Fishes Suffer from Seasickness?

Yes! Like human beings, fishes have a vestibular system. If the sea is rough, they head for the lower and calmer water layers. Sometimes this does not help and they feel sick and throw up into the ocean (yummy!).

Can Fishes be Thirsty?

Considering all the water around them, one might ask oneself: Do fishes need to drink? Yes and no. Even though they do not drink like human beings, they absorb water through their skin.

Flying Fish – Do They Really Exist?

Yes! They do not have wings and do not use little toy airplanes (just joking!). They rapidly flap their tail fin to be catapulted up to 16.4 ft (5 m) into the air.

Climbing Fish – They Also Exist!

Even more impressive than flying fish are climbing fish. The mudskipper has long pectoral fins that it can use like arms. They enable him to climb trees in order to hunt for insects.

There are more than 32,500 species of fish:
Osteichthyes: ca. 29,000
Cartilaginous fishes: ca. 1,100
The most biodiverse animal orders:
Perciforms: ca. 14.400
Cypriniformes: ca. 3,250
Catfishes: ca. 3,400
Eels: ca. 900
Flatfishes: ca. 400
Codfishes: ca. 48

The Remora (suckerfish) rarely swims by himself, but attaches himself with a suction plate to other fish. His "chauffeur" benefits from it: The Remora eats parasites that nest on the skin. What does this have to do with biodiversity?