Introduction to fish

Vertebrates make up around 5% of all animal species of which fish are the largest group, existing for more than 500 million years. The majority of fish species belong to the vertebrates.

Fish exhibit a range of diverse characteristics which makes them one of the most succesful groups of animals in the aquatic environment. They demonstrate a variety of sizes, shapes and diets and inhabitat a range of environments and geographic locations. The smallest known freshwater fish on record is Paedocypris measuring a mere 7.9mm long and live in an extreme niche environment with a pH of approximatley three (NHM, 2006). The largest freshwater fish is the Mekong catfish (Pangasianodon gigas) measuring up to five meters in length and inhabiting oligotrophic (nutrient poor) rivers. (National geographic, 2004).

The majority of fish have a similar body plan. With some exceptions all fish are poikilothermic (cold-blooded0., meaning they reflect the temperature as their environment. The exception to this is a suborder of bony fishes called the Scombroidei and all elasmobranchs (sharks) in the family Lamnidae which are homeothermic (maintaining a higher temperture than their environment). All fish possess gills for breathing and fins to aid movement through the water.

Taxonomy

In addition to the basic body plan, fish have evolved a diverse array of adapted features in order to inhabit a variety of environments. The  detailed taxonomy of fishes is still widely debated among scientists. Below is a basic taxonomic tree of the broad categories of fish.

Diagram adapted from

Jobling, M (1995), Environmental Biology of Fishes, Fish and Fisheries series 16. London: Chapman & Hall.

Nelson, J.R (1984) Fishes of the World, 2^nd Edition, USA: John Wiley & Sons

uBio, Retrieved from http://www.ubio.org/, 21/10/2009