Humphead Wrasse (Napoleon fish)

c_undulatusPhoto: Patrick L.Colin

Cheilinus undulatus

The humphead wrasse is one of the largest of all coral reef fishes, reaching a possible maximum of about 2 metres and capable of living for more than 30 years. It occurs widely in the Indo-Pacific, in coastal waters from inshore down to about 100 m. It is found from the Red Sea and African coast, across the Indian Ocean and much of the Pacific, north to southern Japan and the coast of southern China, and south to New Caledonia.

The species spawns in relatively small to medium size aggregations that have been noted to occur in outer reef areas, usually close to deep water. Not much is known of the aggregation spawning of this species, although groupings of up to 150 fish, that consist of one or several large males and many smaller females have been observed. Fish migrate to spawning areas on a regular basis during the spawning periods, males arriving at the site first, to be joined later by smaller females. Spawning can occur daily and appears to be associated with certain tidal cycles but not with specific lunar phases. Spawning has been noted in many months of the year and lasts for about 60-75 minutes on any one day. The sex ratio in one well-studied location was about 10-15 females per male. ‘Sneaking’ by small males has been observed.

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Male about to spawn a very small female

Male with courtship posture with pointed caudal and anal fins

The humphead wrasse changes markedly in both body form and colouration throughout its lifetime both within the juvenile and adult phases and between adult female and adult phases. The species is known to be a protogynous hermaphrodite, which means that many, if not most, fish change their sex from female to male as they grow older and larger.

Juveniles occur in coral-rich areas of lagoon reefs, particularly among live thickets of staghorn Acropora sp. corals, in seagrass beds, murky outer river areas with patch reefs, shallow sandy areas adjacent to coral reef lagoons and in mangrove and seagrass areas inshore. They tend to move into somewhat deeper waters as they grow older and larger. Juveniles are all, by definition, sexually immature. It takes quite a long time, possibly up to 5 years, with the fish reaching about 35-50 cm in total length, before individuals attain sexual maturation.

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Small juveniles (eg this 6 cm fish) typically live inshore

25 cm long juvenile live inshore

Adults are more common offshore than inshore, their preferred habitat being steep outer reef slopes, reef drop-offs, passes and tops, channel slopes, and lagoon reefs to at least 100 m. They are typically found in association with well-developed coral reefs and may be somewhat sedentary; the same individuals may be seen along the same stretch of reef for extended periods. Indeed, many commercial dive sites have their ‘resident’ Humphead wrasse, a favourite species for divers in many areas.

Population densities are evidently never high, even in preferred habitats. For example, in unfished or lightly fished areas, adult fish densities may range from 2 to 20 (but rarely >10) individuals per 10,000 m 2 of reef. This is very low for a commercially targeted reef species and is more akin to densities of large terrestrial animals. In heavily fished areas, the numbers can drop to at least ten times less than in unfished areas. In some countries the species has become quite rare due to overfishing.

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Adult fish

Large adult with distinctive humphead

Humphead wrasse feed primarily on molluscs and on a wide variety of invertebrates including crustaceans and echinoderms; heavy shells are crushed with the tough pharyngeal teeth and the species also take fishes. It appears to be one of the few predators of toxic animals such as the crown of thorns starfish, boxfishes and sea hares.

Maximum sizes recorded for this species are from Queensland at 2.29 m and 190.5 kg, and 2.5 m and 191 kg. In general, however, fish much larger than 1.5 m are rarely recorded. The reason(s) for this is (are) not clear but it is possible that larger fish are naturally rare, appear to be rare because they are wary, have become rare or occur predominantly in waters deeper than those typically visited by divers, or fished.

The humphead wrasse can live for at least 3 decades. Unpublished age and growth studies using the sagittal otoliths (ear stones) and length data suggest a longevity of at least 32 years for females and 25 for males, if the growth checks in otoliths are deposited annually. On the Great Barrier Reef of Australia, fish attain about 1 metre in total length in about 28 years and sexual maturity in about 5 years. Nothing is known of the natural mortality of the Humphead wrasse. The longevity of the species, however, and our limited knowledge of reef fish biology, in general, suggest that adult mortality is low. It is likely, following the early post-settlement period typically associated with high mortality levels in fishes, that natural mortality drops rapidly after fish settle out from the plankton.

This species spawns (reproduces) in pairs formed within larger social groups that form temporary aggregations. Sometimes spawning aggregations can number several hundred fish in unexploited areas; at other times mating groups are much smaller. Planktonic eggs are released into the water column and drift away from the spawning site. After hatching, the larvae stay in the water until they settle on the substrate. Population sizes and structures are not yet known for this species.

This wrasse is interesting because some individuals change their sex. Adult females are known to change to adult males, a form of sequential hermaphroditism that is found not only in wrasses but in many reef fishes. We do not yet know what controls the timing of sex change, or how ‘decisions’ are made about which fish change sex. Indeed, we still have much to learn about the biology of this species.

(Information extracted from: The humphead wrasse, Cheilinus undulatus: synopsis of a threatened and poorly known giant coral reef fish by Sadovy, Y, Kulbicki M., Labrosse P., Letourneur Y., Lokani, P., and T. J. Donaldson in Reviews in Fish Biology and Fisheries 13(3):327-364)

News from the CITES meeting in Doha, Qatar: http://fishspawning.wordpress.com/2010/04/01/new-from-cites-in-dohanoticias-sobre-cites-en-doha/

(Note that there is an error in Table 7 in the column for the year 2003. The corrected CSD total for January to September is 12,203, the AFCD total is correct at 12,159. All other numbers from the 2003 column should be removed.)

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