Social behaviour of humphead wrasse

 

 Research and education in biodiversity conservation and sustainable use of marine environments of East Malaysia.

 
When carrying out behavioural observations it is imperative that the observer can identify individuals. Many studies involve the use of artificial markers or tags which involve catching, immobilising, and other invasive techniques. The possibility of the artificial tag or marker then altering the natural behaviour of the individual is also then contentious. 

 

During our study, juvenile / small female humphead wrasse were regularly observed in association with blue fin trevally (Caranx melampygus) and longnose emperors (Lethrinus microdon), which hunted in packs across the reef. Small reef fish that darted into cracks and soft corals to evade capture would attract the attention of the small humphead wrasse. The small humphead wrasse was observed to wait beside these refuges, and darting forward to suck up the small fish when they re-emerged from hiding. Colossal adults, which are top (alpha) males, were seen cruising the reefs. These are normally found in deeper water than the smaller individuals. 

A HUMPHEAD WRASSE CRUISING WITH A SCHOOL OF BLUE FIN TREVALLY.

A FULLY MATURE MALE (MEASURING OVER 150 cm) EXHIBITING THE "YAWNING" BEHAVIOUR.

 

The larger fish were occasionally observed  to angle themselves away from the reef wall and yawn in a definite head down posture in the presence of smaller humphead wrasse individuals. The "yawning" behaviour could be seen as a form of communication between conspecifics. 

Between fish there is little aggression except during spawning when large males charge at and chase away smaller males who sneak into the territory. Dominant males are frequently seen with scars and split lips from fighting over harems between the largest males.

 

A LARGE MALE WITH SCRATCHES AND A SPLIT UPPER LIP, WHICH RESULTED FROM FIGHTING WITH OTHER MALES DURING SPAWNING.

 

Humphead wrasse go through 3 life stages, progressing from immature / juvenile fish (measuring up to about 40 cm) to breeding females (between 40 - 90 cm), and finally large males (more than 120 cm and weighing more than 22 kg). 

 

Large green inter-sex individuals (about 90 - 120 cm) changing from female to male usually have a smaller or non-existent hump. 

IMMATURE / JUVENILE INDIVIDUAL (UP TO 40 cm). 

LARGE BREEDING MALE (>120 cm). NOTE THE LARGE HUMP.

 

 BREEDING FEMALE (40 - 90 cm), DARK GREEN  WITH EYE STRIPES, WHITE WITH YELLOW FIN MARGIN. BREEDING FEMALES MAY ALSO EXHIBIT JUVENILE COLOURATION.

 

 

Accurate knowledge of territory size, courtship behaviour and social behaviour will be paramount for successful fish husbandry in the future enabling the rearing of farmed fish for the restaurant trade, thereby reducing the pressure upon natural populations.

 

 

|HUMPHEAD WRASSE IN SABAH|  |HUMPHEAD WRASSE AND THE LIVE FISH TRADE|  |POPULATIONS AND SIZES|  |NATURAL IDENTIFICATION| 

|SOCIAL BEHAVIOUR|  |SPAWNING|