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Tongue-eating louse discovered in the mouth of a fish by a student in South Africa

It is an idea so horrifying that it sounds made up: A parasite which bites off its host's tongue and then replaces it, living inside its mouth for the rest of its life.

But in fact, the tongue-eating louse is real and lives inside the mouths of fish - one of which was discovered recently by a shocked student in South Africa.

Don Marx, 27, from Cape Town, was fishing near Cape Agulhas when he hooked the six-pound carpenter fish and discovered the stowaway inside its jaws.  

Marx, who happens to study marine biology, had heard of the lice but never seen one in the wild - so snapped a picture to document the moment.

Don Marx, 27, from Cape Town, was surprised to find a tongue-eating louse living in the mouth of a carpenter fish he caught off the coast of South Africa

But after he sent the photo to Professor Nico Smit, a zoologist at North-West University, he was delighted to discover this particular species of louse has never been photographed before 

'Being a marine scientist and having fished since a young age, I've see my fair share of parasites living on fish and sharks,' he said.

'But nothing could really prepare me for the moment I opened the carpenter's mouth and saw this blue eyed alien with a moustache staring back at me.

'This specific species of tongue eating louse only uses carpenters as their host and has eluded scientists for years.

The louse enters its host through the gills, bites off its tongue and replaces the organ, living in the fish's mouth for the rest of its life 

'When we allow ourselves to slow down and look around us, nature reveals all of her magic to us.' 

Tongue-eating lice have been known about for decades, but only in recent years have extensive studies begun into their life cycles and behaviour.

It is thought that all species of tongue-eating lice begin their lives as males, drifting in the ocean and looking for fish to latch on to.

Each species of louse - with over 280 identified so far - appears to target just one species of fish.

Once the louse has found a host fish of the right species, it swims through the fish's gills and makes itself at home.

If the host fish does not have any other lice already in place, the new louse makes its way into the mouth, where it attaches itself to the tongue.

Using its front claws, the louse severs blood vessels in the tongue and then feeds by drinking the blood.

During this time, the male will transform into a female - its body increasing several times in size along with its legs, which it uses to latch on to the fish.

Meanwhile its eyes dwindle since it no longer needs to navigate around.

When the fish's tongue eventually dies and falls out due to lack of blood, the louse latches on to the tongue stump and effectively replaces it.

Mr Marx caught the fish off Cape Agulhas (pictured) and was delighted to find that this particular species of louse had never been photographed before

According to a 1983 research paper, the louse 'replaces the mechanical function of the tongue' by helping the fish hold prey against the roof of its mouth while it feeds. 

It is the only known species of parasite that completely replaces the function of an organ in its host.

The parasite will then live in the fish's mouth for the rest of both their lives, feeding on the fish's blood and mucus, but otherwise causing no other harm.

If a louse arriving in a host fish finds that a female is already in place, it will remain as a smaller male and attach to the fish's gills instead.

Males live their whole lives in the gills, occasionally breeding with the female inside the fish, producing live young which are expelled through the gills after birth to find their own host.

It is possible for fish to host several males as well as a female, and in these fish it is common for them to be under-weight - likely due to several parasites feeding on their blood.  

During lab studies, parasites have been seen leaving the mouth of the fish only after it dies, and often cling on to the outside of its head or body.

However, little is known about what happens to lice whose hosts die in the wild. 

It is likely that, as with most parasite species, death of the host means the likely death of the parasite. 

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