Unveiling the Secrets of the Blackspot Tuskfish

By Gomen See, Marine Science Team of Hong Kong Maritime Museum (HKMM)

Blackspot Tuskfish (Choerodon schoenleinii), a colourful reef fish which belongs to the wrasse family, is remarkable not only for their vibrant appearance but also for their complex ecology, including sex change and tool use — traits that little known to the public.

Like many wrasses, Blackspot Tuskfish is protogynous, meaning individuals begin life as females and can later transition to males. This sex change is suggested to be socially regulated: scientist suspected that dominant male uses tactile contact to inhibit the sex change of female within the same group; when the dominant male dies or disappears, the largest female in the group may transform into male. This process involves changes in coloration (males are more bluish, while females are more greenish yellow), behaviours, and physiology.

The biological goal of life is to reproduce as many offspring that can survive and reproduce themselves as possible which can also help to explain the sex change of Blackspot Tuskfish. The evolutionary advantage of this sex change strategy lies in maximizing reproductive success; larger male Blackspot Tuskfish can defend harems more effectively to produce more offsprings, while smaller individuals benefit from starting life as females, which require less energy investment on protecting harem in which they can allocate more energy to produce more eggs, and thus more offsprings.

(Source: Dave Fairclough)

Beyond their reproductive flexibility, Blackspot Tuskfish have also demonstrated an uncommon behavior among fishes—tool use. It is recorded that blackspot tuskfish using rocks to crack open hard-shelled prey like clams. The fish would grasp a clam with its mouth, swims to a selected rock or hard coral, and repeatedly smashes the clam against the rock or coral until it breaks open, allowing access to the soft tissue inside. This behvaiour suggests that Blackspot Tuskfish has certain degrees of intelligence which is quite different from the public understanding in which most people may think that fishes have only a few seconds of memory.

Similar to sex change, tool use also helps the fish to achieve the biological goal. This behaviour helps the fish to expand the types of preys it can feed on and it also greatly improves the efficiency of feeding on certain prey types. It is especially helpful when preys are scarce and the fish cannot select their prey. By feeding on more preys, they will have more energy to defend harem or produce more eggs and thus can produce more offsprings.

(Source: Scott Gardner)

Together, sex-change and tool-using behavior of Blackspot Tuskfish highlight the complexity of ecology and the underestimated intelligence of marine life. Although the two traits are very different in nature, they both help the fish to achieve biological goals - producing more viable offsprings. Understanding these traits not only enriches our knowledge of marine ecology, but also helps us to formulate conservation strategy for the ocean based on the ecology of the wildlife.

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Ocean Guardians Series - Embark on an underwater adventure in Hong Kong with Dr. Connie  

Follow Dr. Connie (Head of Marine Discovery Centre) and her marine friends as they dive into exciting underwater missions. Along the journey, Dr. Connie interacts with various local sea creatures and uses special magic tools to carry out rescue operations. The story highlights the impact of human activities on the marine environment, inspiring audiences to reflect and take action to protect our precious oceans.  

In this episode of Ocean Guardians Series, Dr. Connie (Head of Marine Discovery Centre) heard strange tapping sounds from her old friend, the BlackSpot Tuskfish. Curious to uncover the truth, she decides to investigate! To her surprise, she discovers that BlackSpot Tuskfish mistakes a plastic toy for a clam and is trying to crack it open to eat. Fortunately, Dr. Connie arrives just in time and reminds BlackSpot Tuskfishhas about it. Join Dr. Connie as she shares an amazing story about her reunion with her old friend BlackSpot Tuskfish!