The Danube salmon can reach the size of a man and live for 30 years - but its last hunting grounds in the Balkans are being threatened by a rash of dam-building.
"It's very fast, lean, and elegant. And very beautiful," says Ulrich Eichelmann.
He might have been describing a racing car. In fact, the director of the environmental group Riverwatch is talking about a fish - Hucho Hucho in Latin, Huchen in German, often known as the Danube salmon in English because it was once found in much of the Danube basin.
But its main remaining refuge today is in the Balkans, in the streams and rivers which tumble down the mountains and twist through the valleys between Slovenia and Montenegro.
"We Europeans cry out with indignation about the plight of the last tigers in the wild in Asia, and demand efforts to save them," says Eichelmann, as we trudge though the wetland forest down to the shore of the River Sava in Slovenia. "But we seem blind to the threat to these last tigers of our own - the Danube salmon."
Ahead of him, a man with a white bucket treads gingerly among the snowdrops which carpet the floor of this forest just waking from its winter hibernation. In the bucket are five of the slim blue-green-grey-white-silvery creatures, three years old, each about 40cm long, twisting and turning in the narrow space like teenagers on the dance floor, sensing their imminent release into the wild.
"This fish is a good indicator of the health of our rivers," explains Steven Weiss, an American scientist based in Graz in Austria, and one of the authors of a new study warning that the building of new dams could wipe out many of the fish. They need a lot of space, fast flowing clean water and a very specific habitat to spawn in order to maintain a self-sustaining population.
The ecologists, in alliance with the Slovenian Anglers Association, have brought Danube salmon with them today to humour us journalists, as they launch their campaign to save the fish.
We reach the stony shore. A banner is unfolded. Save the Sava - the name of the river seems designed to fit the English verb. And in a matter of minutes the deed is done.
The racing fish are away, zig-zagging through the shallow waters, over the flat stones of the riverbed towards the rapids nearby.
I first came across this fish in Josef Fischer's garden, beside the Danube in the Wachau region of Austria several years ago. Fischer is a wine grower and angler who breeds thousands of them each year in tanks among his vines.
There's a tank for those several months old, big-eyed creatures filling the space like a sky-full of arrows in slow motion. Separate tanks for one-year-olds, two-year-olds, three-year-olds.
I watched him partially drain his pond, where his prize specimen, a handsome female lay peacefully. He carried her gently to a blue container, made her drowsy with a sedative in the water, then ran his big farmer's hands skilfully down the whole length of her body several times, trying to massage the eggs out of her.
Had he succeeded, he would then have brought a large male fish from another pond to fertilise them. On that occasion, he failed. No eggs. He took it manfully.
"I missed out one stage in the process this year," he explained. "Next year I will go back to the tried and tested method. In the meantime, I have enough fish here already."
Ten thousand in fact, he estimates. Each year, he releases several thousand into the Danube, repopulating the river with a noble species which once migrated up and down it in large numbers. But the many hydroelectric dams built mostly in the 1950s and 60s destroyed their spawning grounds and turned the river into a succession of lakes.
Later, when he had taken off his galoshes, we sipped his crisp white wine and watched the afternoon sun light up the ruins of the castle where good King Richard of England was once imprisoned, on a hilltop on the far bank. "I haven't eaten this fish for 10 years," Fischer confessed. "I like them too much."
On the River Sava, Weiss explains how salmon breed in the wild. The queen finds a section of riverbed she likes the look of, the king sidles alongside, they perform a dance together, sweeping away the fine grains of gravel to make a nest to lay her eggs. And as she does so, he sows his own seed over them like a sudden underwater cloud.
When its all over, she sweeps a fine film of sand over the eggs with her tail. A month or so later, small fish emerge. Princes and princesses of the Balkans.
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