Facts
Most Fish are cold-blooded, their body temperature varying with the surrounding water. Many Fish can communicate acoustically with each other, such as during courtship displays
Fish have been an important natural resource for humans since prehistoric times, especially as food. Commercial and subsistence Fishers harvest Fish in wild Fisheries or farm them in ponds or in breeding cages in the ocean. Fish are caught for recreation, or raised by Fish keepers as ornaments for private and public exhibition Fish have had a role in human culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.
Fish species are roughly divided equally between freshwater and marine (oceanic) ecosystems; there are some 15,200 freshwater species and around 14,800 marine species.
Fish exchange gases using gills on either side of the pharynx. Gills consist of comb-like structures called filaments. Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide.
The digestive system consists of a tube, the gut, leading from the mouth to the anus. The mouth of most Fish contains teeth to grip prey, bite off or scrape plant material, or crush the food. An oesophagus carries food to the stomach where it may be stored and partially digested.
Fish have small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.
The primary reproductive organs are paired testicles and ovaries. Eggs are released from the ovary to the oviducts.
