Fishes are a highly diverse group of vertebrates. They include the cartilaginous fishes (sharks, skates, rays, chimera), the ray-finned fishes (paddlefishes, spoonfishes, pipefishes, seahorses, sturgeons, to name just a few), and the lobe-finned fishes (coelacanths and lungfishes).
Despite their diversity, fishes remain relatively unfamiliar to many people. These facts are only a tiny fraction of the available information about fishes but will help get you started down the path of learning more about this amazing group of animals.
1. Fishes were the first animals to posses backbones.
The first fishes appeared approximately 500 million years ago. These primitive fishes had a notochord but no jaw bones or teeth. It was not until 440 million years ago that fish with jaws and teeth first appeared.
2. The term 'fishes' is an informal label and does not represent a taxonomic group.
The classification of fishes is quite complex and does not include a group that corresponds to 'fishes' as we would think of them. Instead, there are several classes and superclasses that together make up what is commonly understood as 'fishes'.
3. The ray-finned fishes (Class Actinopterygii) are the largest group of fishes.
There are nearly 24,000 species in 431 families of ray-finned fishes. They are very diverse and inhabit a wide range of habitats, some of which are quite harsh.
4. Some species of fish migrate between freshwater and marine environments to spawn.
Such species are referred to as diadromous. They are further described by the direction of their migration. Fish that migrate from the sea into freshwater rivers to spawn (for example, salmon) are described as anadromous. Fish that migrate from a freshwater environment to the sea to spawn (for example, freshwater eels) are described as catadromous.
5. Fish move by creating a wave motion that moves the length of its body.
This wave motion begins at the head and moves to the tale where the resulting side to side motion produces thrust to move the fish through the water.
6. Fish are cold-blooded (ectothermic) animals.
Their internal body temperature is therefore the same as the surrounding water.
7. Many species of cichlids brood their eggs in their mouth.
After the eggs hatch the parent continues to use their mouth to provide shelter for their young.
8. There are two groups of jawless fishes alive today.
Once a diverse group of fish that appeared over 500 million years ago, jawless fishes are today represented only by lampreys and hagfish.
9. Cartilaginous fishes include the sea's largest and most skilled marine predators.
These include sharks, skates, rays, and chimeras. These fish have skeletons made from cartilage, not bone. The cartilaginous skeletons are more flexible than bone.
10. The lateral line system on some fish detects variations in water pressure.
This helps fish detect prey and avoid predators.
