A school of reef fish

Fish are aquatic, cold-blooded vertebrates that breathe by means of gills and use fins to move around.

Fish are divided into two main groups: bony fish such as hake, tuna, sole and trout, which have a bony skeleton – and the cartilagenous fish such as sharks and rays, which have an inner framework made of cartilage.

Fossil records indicate that fish have been around for more than 360-million years. During this incredibly long period they have achieved great diversity and have become adapted to life in nearly all aquatic habitats. There are over 20 000 fish species worldwide which makes them the vertebrate group with the largest species diversity.