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Species: the Napoleon fish

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Species: the Napoleon fish

The Napoleon fish, also known as the humphead wrasse and Maori wrasse, is one of the largest reef fishes in the world. Males can grow to over 2m, females are slightly smaller with an average length of around 1m. The fish can weigh up to 190kg.

Napoleon fish are found throughout coral reefs in the Indo-Pacific region on steep slopes at 1 to 100m in depth. Napoleon fish are distinguished by their large size, thick fleshy lips, and the hump above their eyes which becomes more prominent with age. Males vary in colour from electric-blue to blue-green to blue-purple. Females are red-orange in colour and their undersides are lighter than the top of the body, sometimes even being white. Juveniles look similar to females but have stripes at the side of their eyes. The Napoleon fish can live up to 30 years and does not reach maturity until it is between 5 and 7 years old.

Napoleon fish are protogynous hermaphrodites; this means that the individuals first become reproductively active as females and then may become males later on in life when they have reached a larger size. The triggers for this transition are not currently known.

Napoleon fish are opportunistic predators and feed on crustaceans, molluscs and fish. The ability of the fish's tough teeth to crush shells enables them to feed on a large variety of fish and invertebrate species. They are one of the few species of fish that predates on toxic species such as the crown-of-thorns starfish. Their ability to eat crown-of-thorns starfish and other organisms that predate on corals means that Napoleon fish are vital to the maintenance of a healthy coral reef ecosystem. They are active during the day and return to a favoured cave or ledge to rest at night. Adults tend to be solitary but pairs will spawn together as part of a large mating group that may include as many as 100 individuals.

Their large size means that they have no natural predators apart from large sharks. Although never common, Napoleon fish are becoming increasingly rare as a result of overfishing. They are considered a delicacy in certain parts of Asia and as such have been exploited. They are normally caught by cyanide fishing which is extremely damaging for the coral reefs where Napoleon fish live.

The Napoleon fish is listed as endangered on the IUCN Red List and some countries have taken measures to protect the fish.

For example, catching the fish has been banned in Australia while in other countries, fishing permits are required in order to capture the fish and there are bans on the import and export of the species. The WWF and other organisation are working to protect the Napoleon fish by helping to ensure sustainable fishing practices worldwide. Changes to public attitudes towards the fish are also required to reduce demand for this fish. However, the long life cycle of the fish means that it will take many years before Napoleon fish populations begin to increase again even if all exploitation stops immediately.

Author : Anja Mizdrak