Lesson 1, Topic 1
In Progress

The great diversity of fish and their main characteristics

The Great Diversity of Fish

reflects different adaptations that enable fish to live in the oceans and fresh water. Fish vary in size and shape, and can be divided in 3 main groups (above). 

Fish by the Numbers

According to FishBase, 34,300 species of fish had been described as of September 2020. That is more than the combined total of all other vertebrate species: mammals, amphibians, reptiles and birds. Fish species diversity is roughly divided equally between marine (oceanic) and freshwater ecosystems.