The ecological role of cleaner wrasses of the Indo-Pacific region provides a good example of the complexity of seemingly mutualistic relationships between fishes. Typically, cleaner fishes are elaborately colored and perform displays over a patch of reef while larger fish approach and assume a relaxed posture. Cleaner fishes are commonly thought to benefit the host by removing dead or damaged tissue and ectoparasites. Accordingly, investigators reported higher recovery rates for wounded fish in the presence of cleaners. However, in experiments where all cleaners were removed from an environment there was no incidence of fishes leaving the area or becoming particularly unhealthy. Further, when levels of parasitic infections are high the host benefits from cleaning but when infection levels are low, which they usually are, some cleaners feed on healthy tissue, such as scales, pieces of fin, mucous, or in some cases the eggs of other reef fishes. Despite these parasitic qualities of the relationship, fishes being cleaned have a positive response to the tactile stimulation from cleaners, suggesting that some cleaners are mildly beneficial while others have taken advantage of the cleaning arrangement.

The relationship between wrasse species and their invertebrate prey is a spectacular example of coevolution. As invertebrates have developed anti-predator adaptations, such as spines, toxins, heavy armor, and adherence to the substrate, wrasses have evolved simultaneously. Some physical changes include the development of strong, hard beaks and a second set of strong teeth in the throat (  pharyngeal jaw), making it possible to crush hard-shelled invertebrates. A conspicuous behavioral adaptation is “following behavior.” As larger fish disturb the substrate, some wrasses follow close behind to capture exposed invertebrates. Other small wrasses have become adept at combing the reef for invertebrates too small for most fishes to prey upon. Finally, some wrasses use their snouts to flip rocks and pieces of coral to expose hidden invertebrates.

Ecosystem Impact: parasite

Species Used as Host:

• some fishes

Mutualist Species:

• many fish species