He's not making this up.
It's known as
Proteus anguinus and even though it's called a
human fish it's actually an
amphibian of the
Proteidae family and is distantly related to the newt. The creature was known locally as the
Mocheril, which in
Slovenian means "the one that burrows into wetness." It is the only known cave
amphibian and the largest among proper cave animals.
It's usually about 25
centimeters long when fully grown, with a flat tail and a swimming fin. It has two pairs of legs. Living deep
underground, it's completely adapted to the dark with no
pigment in its skin and eyes that have atrophy once the animal passes the foetal stage. Its whole body, though, is extremely sensitive to light, smell and electrical currents. It's not an effective
predator: it has a blunt muzzle and small teeth, but it eats small animals, shrimp, and insect larvae. it can survive without food for a surprisingly long time (one test showed that in one instance in captivity it fasted for twelve years).
Very little is known about their reproduction. And, given the difficulty of getting to their favoured locations, little is known about the extent of the population. The habitat is very limited - deep underwater caves and rivers in
Slovenia, a few square miles in
Italy and
Croatia, and the territory reaching down to
Bosnia and
Herzegovina.
They reach
maturity at 12 to 14 years, and can live to be a hundred.
First written about in 1689, and thought to be the offspring of a
dragon, this creature was captured by a local postman and put on display. Where the world promptly forgot about it until 1750 when a fisherman snagged five legged fish in his net. A single specimen was sent abroad, and forgotten about within fifty years despite the intial fights about what exactly it was and the naming of the creature. (It was named by a Viennese
zoologist, J N Laurenti, after the Greek god
Proteus, shepherd of the creatures of the sea.)
It bamboozles scientists with several of its habits: most particularly the fact that it reaches sexual maturity when still in its larval stage. It doesn't finish its
metamorphosis, from the
tadpole-like stage breathing with
gills to leaving the water. Even though it has rudimentary
lungs, it remains in the water, using its gills.
I'm more worried that something ten inches long with gills, four legs and no eyes is said to look like a human...
most of this information digested from Diver magazine