The animal on the cover of Learning WCF is a marine fish commonly referred to as a damselfish (demoiselle). Damselfish and clownfish comprise the family Pomacentridae and are found in tropical waters throughout the world, though mainly in the Atlantic and Indo-Pacific oceans. The damselfish, of which there are about 250 species, has a deep, compressed body, a small mouth, and an anal fin with two (occasionally three)spines. Its average length in captivity is about 2 inches, but in the wild, the largest member of this subfamily reaches over 14 inches.Coloration varies according to species, location, and age; these fish often lose their brightness as adults.
Because damselfish are extremely hardy, they are often captured and bred in aquariums.They are sometimes used to break in a new aquarium, but this is considered an old-school practice and is frowned upon by advanced aquarists. In captivity,damselfish can become quite aggressive among themselves and toward other tankmates,disrupting an otherwise peaceful environment. In the wild, they tend to stay in small schools while young and eventually break away to become solitary as adults.
Some damselfish live with anemones in a comensal relationship, meaning that each party benefits from the arrangement. In its natural habitat, this entertaining little fish can live up to 20 years.