Proteus anguinus is an amphibian: a pale, stretched cousin of the newt. Its development and lifestyle have been shaped by several million years of living in dark, subterranean caves in central Europe. Arne Hodalic dived to photograph this rare creature in the water-flooded caverns of Slovenia where, because of its pallid skin colour, it is known as the 'human fish'.
I STARED into the dark green water, wrapped myself into my parka and shoved my hands deeper into my pockets. Half-hearted jokes could not conceal the tension between us - in a few minutes we would dive into the icy Divje Jezero, the "Wild Lake", and swim into the deepest-known siphon in Slovenia.
We were in pursuit of the Proteus, the mysterious denizen of underground waters. Until now, no one had succeeded in photographing one in its natural environment. Could we really do it?
I had met Olivier Isler, probably one of the best cave divers of all time, by coincidence. He had listened to my stories about the wonders of the Slovenian underground world with great interest and had become infected with my enthusiasm.
One thing had led to another and my doubts about whether or not cave diving was sensible were driven away by the desire to explore the new and unknown.
But what made this extremely busy Swiss cave diver change his carefully planned schedule? It must have been the possibility of swimming in an unknown sump, along with the little pale animal that, because of its skin-colour, had acquired the local name "human fish". But what was so special about this fragile creature?
The human fish is a member of the family of amphibians, Proteidae. The family comprises only two genera: Necturus, with a few species indigenous to surface waters in North America, and Proteus, with only one species, Proteus anguinus, living in the waters of the Dinaric Karst in the area between Slovenia and Herzegovina.
As early as 1689, the famous chronicler of the province of Carniola, Baron Valvasor, wrote about the fear and astonishment of local inhabitants when an immature "dragon's young" was found at a tiny water source. The postman who found it, Mr Hoffman, took it home and put it on display.
Later, having spoken to the "brave" imperial postman, the honourable Baron admitted that this so-called dragon "was only a span long and looked like a lizard". In short, it was an underground worm.
People had forgotten about this little monster when, in 1751, a fisherman caught five creatures that looked like four-legged fish and were white as snow. When he threw them out of the stake net, he said they started "screaming and squealing".
The creature came to be 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.
One of the characteristics of amphibians is metamorphosis; when the larva or tadpole living in water and breathing with gills develops into an adult, it leaves the aquatic environment and breathes with lungs like a land animal.
But the human fish appears not to complete the metamorphosis; it reaches sexual maturity as a larva. So far, science has not entirely explained this phenomenon, known as neoteny, but one thing is certain - this peculiarity is somehow connected to the production of the hormone thyroxine, despite the fact that Proteus does not react to the substance in the way other "normal" amphibians do. A number of scientists have tried to force the Proteus to metamorphose, but in vain. The animal stays in water its entire life and breathes with gills, even though it has rudimentary lungs.
In the 18th century, the famous Swedish scientist Carl von Linne crossed swords over the creature with the Slovenian scientist Giovanni Scopoli, who wrote: "Respected Linnaeus, to whom I sent the picture, is of the opinion that it is the larva of some lizard. I feel that Proteus is a separate animal genus." He was right.
Scopoli could not keep his enthusiasm about the discovery to himself. He sent several animals preserved in alcohol to scientists all over the world while he prepared to make his great discovery public.
In the meantime, a Vienna doctor and zoologist, J N Laurenti, admired this unknown animal that Scopoli had sent to a friend of his. Laurenti beat Scopoli to the punch and entered history as the discoverer of a new animal species. He called it Proteus anguinus after the Greek god Proteus, shepherd of the creatures of the sea.
Scopoli was left empty-handed, and Laurenti won fame without even being certain where his "discovery" came from. In any case, he named the Cerknisko Jezero lake as the place of his discovery and it subsequently enjoyed the fame of an Austro-Hungarian Loch Ness.
Towards the end of the 18th century, the French Revolution and the rise of Napoleon cast a shadow over scientific discovery. People somehow forgot about the human fish - only one specimen, which Scopoli had sent abroad, remained. It was covered in dust on the shelves of a Vienna museum.
When, in 1795, the "Keeper of the Imperial-Royal Repository of Natural Specimens", Karl von Schreibers, was rearranging the vast collection, he caught a glimpse of the forgotten human fish. He dissected this extraordinary animal and found its anatomy so fascinating that he decided to study it in greater detail.
He had several live specimens brought from distant Carniola, which was no Sunday outing in those days of slow horse-drawn carts. Only a few of the toughest survived the long journey to the capital. Schreibers bred the Proteuses in artificial underground caves, and published the results of his close observations in the Philosophical Transactions of the London Royal Society.
The human fish instantly won the sympathies of the entire scientific world. Suddenly it seemed everybody wanted to see and study this rare creature. Trade in the animal flourished in Carniola and, ever since, enterprising locals have been strongly attracted to this profitable "business". Today, thankfully, the human fish is on the list of the Washington CITES Convention, which prohibits trade in rare wild animals.
Not because of environmental concerns, about which Schreibers in 1806 did not have a clue, but because of high demand and the high mortality rate of these sensitive animals in transit, the Vienna scientist designed a wax model cast after a particularly beautiful specimen. This was the only survivor of a fire which, in 1848, destroyed the entire documentation that Schreibers had amassed in the Vienna museum.
THE human fish, completely adapted to the dark, hides in the depths of underground sources far from our curious gaze. The pale skin contains no pigment, and the tiny eyes can be seen only at the foetal stage - later they atrophy and are grown over with skin.
Approximately 25cm long, the animal has a flat tail surrounded by a skin-like fin which is used for swimming. Its Latin species name anguinus (meaning snake) comes from its snake-like appearance. It has two pairs of legs and the entire body is more or less sensitive to light. It has an excellent sense of smell, and probably has a highly adapted sense for weak electrical currents, which would partly explain its orientation abilities in the darkness of the cave environment.
The Proteus breathes in three ways. On either side of its body, at the back of its head, there are three pairs of extended gills, bright red with excellent blood circulation. It also has a simple pair of lungs and, when out of water, it can breathe through its skin.
It eats small animals, such as the shrimp-like Troglocaris schmidti, amphipods and the larvae of various insects. Sometimes, under the cover of night, the human fish will swim to the cave exit to hunt for small surface-water animals.
Cannibalism is not unusual but a fully grown animal can attack only the very young, as its blunt muzzle and small teeth do not make it a very effective predatory beast.
Proteus is fascinating in its ability to remain in captivity without food for an unbelievably long time. There are reliable reports about the length of its fasting, with one surviving for 12 years at the Faculty of Biotechnology in Ljubljana. It was kept alive in a small jar and held in a refrigerator at 6*C to simulate the animal's natural habitat.
The animal was eventually sacrificed for research purposes - when the scientists dissected the body, which by this time was very weak and thin, they found that the creature's digestive system had completely disappeared.
Proteus's metabolism must be extremely decelerated, because the animal reaches sexual maturity between the ages of 14 and 18, and can reach the grand age of 100.
Little is known about its reproduction. Divers have been known to swim through miles of siphons and underground lakes, researchers have tipped up countless stones, but so far nobody has seen where or how the life of this mysterious creature begins.
The zealous Schreibers was determined to find out. He offered a very high reward of 25 gold coins to whoever could bring him a female carrying ripe eggs or foetuses.
This tempting offer was published in the Ljubljana newspapers. The number of captured and killed animals soon ran into thousands, but Schreibers' reward remained undisturbed. We can only assume that Proteus reproduces deep in the peaceful and inaccessible watercourses of the cavity-filled, or karstic, underground. There is no doubt that the human fish lays eggs - this has been confirmed by laboratory cultivation. But there are also two or three unconfirmed cases of these creatures giving birth. The experiments date back to 1928, when one of the first laboratories in a natural cave was established in Slovenia. The chief goal was the reproduction of Proteus.
Years passed without any success. Then, in the 1950s, a modern underground laboratory was established in Moulis in the French Pyrenees. The French got the necessary permits, gathered together a few Proteuses and began experimenting. It was six years before they got any results.
The animals laid approximately 70 eggs, and incubation of the foetuses lasted several months. Although there had been earlier reports on reproduction with eggs in captivity, the French experiment in an artificial cave environment was scientifically supervised and properly documented.
The habitat of the human fish is very limited. It is mainly found within the territory of present-day Slovenia, a few square miles in Italy and Croatia, and the territory reaching down to Bosnia and Herzegovina.
Schreibers noticed that animals from different sites varied slightly in colour and shape. This led to descriptions of seven diverse species, which soon proved to be the result of exaggeration by over-zealous natural scientists.
In 1986, the high waters of a karstic source in the Bela Krajina region washed up a completely black Proteus. The discovery would not have surprised anyone, for it is well known that the white Proteus turns almost black when exposed to light for a long time. However, it appeared that this specimen was different in shape and had less-atrophied eyes.
Diving into the source did not produce any results, but fortunately another, more abundant site was discovered nearby. So far, the number of specimen finds does not go beyond 20, but a quite homogeneous population of black Proteuses, or Proteus anguinus parkelj, is thought to live in a tiny part of Slovenia, no bigger than 50 square miles.
Research shows that the black population is probably a sub-species of the white human fish but it is more akin to its surface ancestors. Due to the difficult access to the genuine Proteus habitat in the karstic underground world, and the high number of caves yet to be discovered, it is impossible to estimate the size of the Proteus population, white or black.
Meanwhile, nervous and shivering with cold on the snowy shores of a small lake, it was time to embark on my first cave dive.
I instantly forgot about the icy cold and threatening blocks of rock above my head when, in the weak light of the flashlight, I saw a transparent white animal slithering through the green-black water, purposefully swaying its tail fins. In the narrow space of the underground sump, the Proteus swam away from the disturbing light and tried to avoid Olivier, who floated motionlessly just above the floor a short distance away.
It did not succeed. They touched for a brief moment in time - the human and this ancient animal species which has been living in the silence of the underground world for millions of years.
What a contrast! The cave diver, caught in the complicated system of breathing tubes, pipes, manometers and all kinds of instruments that enable him to survive in a lethal environment, faced this sensitive creature which is so completely adjusted to his unwelcoming world of darkness.
As if amazed, the Proteus shrank back and swam towards the dark rocks lying scattered around the bottom. I remembered that the human fish does not have a single enemy in its natural environment and that an adult animal can swim freely in the underwater labyrinths without having to fear the slightest danger.
When I looked at Olivier and myself, having barged into this once untouched world like two terrible beasts, this sad thought came flashing into my mind like a sharp pain: Proteus does have an enemy, the worst and most merciless of all - the human.
Appeared in DIVER - September 1997