The first ray-finned fish appeared during the Devonian Period and underwent significant expansion and diversification during the Carboniferous Period. The first actinopterygiians evolved in freshwater but they later expanded into marine habitats.
Ray-finned fish possess the following basic characteristics:
- bony skeleton - the skeleton of ray-finned fishes is made up of true bone
- an upper jaw that consists of two bones - the two bones that form the upper jaw of ray-finned fish are the the maxilla and the premaxilla
- fins with bony spines - the fins of ray-finned fishes consist of a set of bony spines that are covered with a thin layer of skin, which contrasts with the sarcopterygiian fish, a group of fish whose fins consist of fleshy lobes
The two-boned structure of the upper jaw in actinopterygians has proven highly adaptable. This structure makes the upper jaw protusible (easily extended) and as a result, a wide range of feeding adaptations have developed in actinopterygiians.
Many actinopterygians face significant threats from humans including habitat destruction, over-exploitation through commercial fishing, and pollution of the waters in which they live.
Classification:
Range and Habitat:
- Temperature: -1.8°C–40°C
- pH: 4–10
- Salinity: 0–90 ppm
- Depth: 0–7,000 m
- Oxygen Saturation: 0–saturation
Regions with high diversity of freshwater species include the Amazon River Basin and the rivers and wetlands of Southeast Asia. Marine species are most diverse around coral reef systems such as the Great Barrier Reef. Some species of ray-finned fishes are capable of migrating between fresh and salt water, and are therefore considered diadromous. Some species such as salmon make a migration from saltwater upstream to freshwater where they spawn. Other species such as freshwater eels migrate from freshwater to salt water to spawn.
References:
- Burnie D, Wilson DE. 2001. Animal. London: Dorling Kindersley. 624 p.
- Jonna R. 2004. Actinopterygii, Animal Diversity Web. October 12, 2007.
