fishes (Pisces, from the Latin piscis = fish) are aquatic vertebrates with gill respiration. The class of fish does not describe a self-contained class, as is the case with mammals, birds, amphibians or reptiles, but summarizes a group of morphologically similar animals.
Historically, the first fish appeared in the Ordovician about 480 million years ago. Today, biologists distinguish between 33,000 species of fish, and this number is constantly being revised upwards as new species of fish are still being discovered.
In principle, two types of fish can be distinguished:
cartilaginous fish: Skeleton of cartilage, e.g. Shark and rays
bonefish: Skeleton of bone, e.g. Salmon and catfish
Note: Although the shape or habitat suggests, whale, penguin and dolphin are not fish.

Characteristics of the fish:

The class of fish combines some characteristic features, including e.g. the gill breathing, fins for locomotion and scales as a protective armor. However, it may happen that isolated fish species do not have all the characteristics listed here. The reason for this is the long phylogenetic development, in the course of which z.T. developed very different manifestations.
fins: To move, fish use their fins.
procreation: Most species of fish do not copulate. Fertilization of the eggs takes place in the water.
sense of smell: By far the best developed sense of fish is the sense of smell. Visually, fish only badly perceive their environment.
Kiemenatmung: Fish take the oxygen released in the water via the gills.
spawn: Fish hatch from eggs, the so-called spawn. There are also live-bearing fish, but even with them the fish develop from eggs, but in the body of the fish.
Poikilothermie: All fish are hotter. Your body temperature is essentially determined by the outside temperature.
mucous glands: Beneath the scales are mucous glands. The secreted secretion protects against bacteria and reduces the frictional resistance in the water, so that fish can swim faster.
shed: The scale armor protects the fish against mechanical influences from the outside.
swim bladder: All bony fish are in possession of a swim bladder. This allows fish to regulate the buoyancy in the water.
Lateral line: The lateral line organ is a special sensory organ to perceive movements. The corresponding sensory cells are located on the left and right sides of the body.
vertebrates: As a vertebrate fish have a spine.

List of fish:

Eel, frogfish, brown trout, barbel, barracuda, blob fish, clownfish, cod, flounder, perch, trout, goldfish, guppy, shark, hammerhead, pike, cod, carp, dogfish, koi carp, puffer fish, salmon, mackerel, moderlieschen, Sunfish, Moray Eel, Piranha, Burbot, Coelacanth, Rainbow Trout, Ray, Redfish, Anchovy, Tench, Plaice, Swordfish, Seahorse, Turbot, Sturgeon, Tiger Shark, Tuna, Catfish, Pikeperch, Eel