February 10, 2011 : Clownfish

Clownfish

Clownfish or anemonefish are fishes from the subfamily Amphiprioninae in the family Pomacentridae. About twenty-nine species are recognized, one in the genus Premnas, while the remaining are in the genus Amphiprion. In the wild they all form symbiotic mutualisms with sea anemones. Depending on species, clownfish are overall yellow, orange, reddish or blackish, and many show white bars or patches. The largest can reach a length of 18 centimetres (7.1 in), while some barely can reach 10 centimetres (3.9 in). In popular culture, "Finding Nemo" by Pixar / Disney prominently features clownfish as the main characters.

Clownfish are native to warmer waters of the Indian and Pacific oceans, including the Great Barrier Reef and the Red Sea. While most species have restricted distributions, others are widespread. They are generally highly host specific, and especially the genera Heteractis and Stichodactyla, and the species Entacmaea quadricolor are frequent partners.

Clownfish live at the bottom of the sea in sheltered reefs or in shallow lagoons, usually in pairs. They are also found in northwest Australia, southeast Asia, Japan and the Indo-Malaysian region. There are no clownfish in the Caribbean.

Clownfish live in pairs inhabiting a single anemone. When the female dies, the dominant male changes sex and becomes the female. This life history strategy is known as sequential hermaphroditism. Because clownfish are all born as males, they are protandrous hermaphrodites (pro=first; androus=male). On the top of the hierarchy is the reproducing female followed by the mating male. Below them are a bunch of non-mating males. But, if the female dies, the whole hierarchy gets disrupted. The predominant male then morphs into a female and chooses a partner from the various non-mating males. The largest fish in the group is a female and the second biggest is a male. All the other clownfish are neuter, which means they have not fully developed functioning sex organs for either gender. If the female should die, the male will change sex, while the biggest neuter clownfish will develop functioning male sex organs to replace the male.

In a group of clownfish, there is a strict hierarchy of dominance. The largest and most aggressive female is found at the top. Only two clownfish, a male and a female, in a group reproduce through external fertilization. The clownfish are hermaphrodites, meaning that they develop into males first, and when they mature, they become females. Also, as mentioned earlier, more than one clownfish is able to live in a sea anemone. If the female clownfish is removed from the group, such as by death, one of the largest and most dominant males would become a female. The rest of the remaining males will move up a rank on the hierarchy.