K's Kreature Feature is an educational presentation at our monthly general staff meetings here at the Two Oceans Aquarium, but it’s only right that we extend the knowledge and fun to our readers here on our website. Every month Education Operations Co-ordinator Katja Laingui presents a different animal that we have here at the Aquarium and tells our colleagues more about it. Usually she uncovers some rather interesting facts about the various animals she researches. She also makes sure to entertain her co-workers…

This Kreature Feature has been on my radar for years, but for some reason I've never researched it further. Possibly because it gives normal people the creeps.  

Image source: Wikimedia

I am not talking about the fish - look closer, into its mouth. That thing in there is an isopod. A "tongue-eating isopod" to be specific. The name really is very descriptive because that is exactly what it does: it eats the tongue of its host fish.

Let's back up a little. What exactly is an isopod? "Iso-" is a prefix derived from the Greek word "isos" which means "equal" or "the same". The word "pod" means "foot". So an isopod is an animal that has feet that all look the same. A common one, that sends many beachgoers shrieking the other way because "something touched my leg", is a little isopod called the beach louse. They are often met in swarms, feasting away at some dead kelp or fish. 

The tongue-eating isopod has evolved into a very specialised animal that survives on the blood of fish to survive. Essentially, it is a marine vampire with a preference for tongues. Weirdo. There are 380 different species of tongue-eating isopods, most of which usually have a specific species of fish that they invade. This particular form of existence is ectoparasitic. "Ecto-" means outside, signifying that this is a parasite that lives on the outside of the animal or at least not within its digestive system or in the blood stream. 

The various species are widely distributed all around the world, with most of them living in tropical and sub-tropical waters

The specific species that prompted me to make tongue-eating isopods my Kreature Feature is a cold-water species which lives in South African waters. It has no common name; it was only discovered in 2014, which is extremely recent in comparison to many other species that were discovered and described two centuries ago. The scientific name is Ceratothoa africanae. "Cera-" comes from the Greek word keratos which means horn. Its species name was derived from the ship it was discovered on, the Afrikaner.

Tongue-eating isopod inside the mouth of a steentjie. Photo by Nicholas Nicolle

Two Oceans Aquarium Senior Aquarist Nicholas Nicolle showed me photos of a postmortem he did on a steentjie (Spondyliosoma emarginatum) from one of our exhibits. Apart from the fish, Nic also found a rather large isopod sitting snugly in the mouth. Tongue-eating isopods are host-specific, which means that the Ceratothoa africanae isopod will only live inside a steentjie. However, on its journey to find a steentjie, the isopod will parasitise other species of fish and "hop" from one to the other.

The effects of tongue-eating isopods on their hosts are not pretty. Firstly, they release anti-coagulants which prevent the fish’s blood from clotting. They feed on the blood by attaching themselves to the tongue of the fish (yes, fish have tongues) so that they can grow and get bigger. The tongue eventually atrophies and falls off. Initially the host fish will suffer from anaemia, but ultimately there will be a slowing growth rate and tissue damage. The inevitable result is death, since an isopod in the mouth prevents the fish from feeding properly and leeches all of the remaining nutrients out of the fish’s body.

The isopod can get pretty large and take over the whole mouth cavity of the fish. Photo by Nicholas Nicolle

But all good (in this case bad) things come in twos. Tongue-eating isopods are protrandrous hermaphrodites. This means that there is a dominant, large female with a smaller male. Should the female die, the male will then grow and turn into a female. The new female will attract a new male and they will live happily ever after ... until either dies.

The smaller male also lives in the host fish, but usually in the gills. Photo by Nicholas Nicolle

Another very popular animal that is a protrandrous hermaprhodite is the clownfish. So when Nemo’s mom dies in the beginning of the movie (spoiler alert!), Marlin, Nemo’s dad, should have become Marlene.

Tongue-eating isopods have clearly fascinated people for a while. They have featured in popular culture, such as in an episode of QI, they have been the main theme of a book, and the stars in a movie about tongue-eating isopods that take over humans and control their brains.

However weird they are, every animal on this planet has a role to play and, who knows ... Next time you walk past a fish at the Aquarium, it might have an extra passenger on board.

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