Tongue-Eating Isopod – Opens Clownfish Mouth

Most divers if not all divers are profoundly attracted to this colourful and well described marine critter the Clownfish.

However the less known aspect of the Clownfish is the existence of this unusual behaviour of a parasitic isopod  that make the Clownfish mouth stay wide open continuously. This less known aspect is however a curiosity among divers and also underwater photographers. Often during our dives, we noticed Clownfish with its mouth wide open. The reason it is doing so is because of a tongue-eating isopod that has invaded the mouth of the Clownfish and has become attached to the base of the mouth of the affected Clownfish.



The tongue-eating parasitic isopod is the Cymothoa species. There are many species of the Cymothoa isopods. However, each species of the parasite is attached to a specific host, it has been observed.  So far, only the Cymothoa species isopods are known to the only isopods that consume and replace the organ of the hosts.

The parasitic isopod enters the fish through its gills and then move towards the fish tongue.  The male isopods attach themselves on the gill arches of the fish and the female isopod/s attach themselves  on to the tongue. Normally there is only one female isopod in the group. The female isopod then feed on the blood supply of the tongue causing it to atrophy and fall off. It then attaches itself to the base of the fish tongue to become the fish “pseudo tongue”. There appears to be no damage to the fish except that the tongue has been replaced and the isopod becomes the fish tongue. As a result of this parasitic isopod invasion, the mouth of the Clownfish becomes wide open continuously.

Here’s another interesting observation that led me to further study this unusual behaviour of the Clownfish and the life-cycle of the parasitic isopod, the Cymothoa.

Diving and underwater photography can help us to have a better and keen sense of observation and provide new aspects and avenues for us to explore nature further in depth.

Our dive experience  allows us to see more and be more discerning, through this, we will be able to discover more. Even common observation can stimulate interesting study and challenge us to pursue deeper study in the field of science and discovery.

Enjoy your dive experience and continue to share what you have observed. Have fun and dive safe always!











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