Fishing Lines: Doctor slug in the mud

THE neighbour was very apologetic. 'We've got this creature in our dried-up pond and we're not sure what it is. We rather hoped you might come and capture it. It's about two feet long and looks like a giant slug,' he added.

What do you take to capture a two-foot slug? A spear? A club? A bag of salt? Surely not a rod. I compromised and fetched the giant landing net, specially for monster pike and salmon but so far, alas, unsullied by anything except an unusual butterfly.

I was convinced the Creature of the Black Lagoon would be an eel. On dark summer nights, when the ground is damp, eels will travel across land to find new homes. It is not unusual to drain a lake or pond and find almost black eels, like snakes from hell, hiding in the sludge.

But when I saw something stir, I realised it was not a swamp monster or even a huge slug. It was something as slimy as an eel, but not quite as repulsive: a tench, once called the doctor fish. This name comes from the belief that tench are physicians to other fish, especially pike. In perhaps the earliest angling book, A Treatyse of Fysshynge wyth an Angle, Dame Juliana Berners says the tench 'heelith all manners of other fysshe that ben hurt yf they maye come to hym'. Walton believed that pike would not eat tench, and 'forbears to devour him though he be never so hungry'.

Nonsense it may have been, but early physicians regularly used essence of tench slime, along with powdered bits from the fish's ears, in their potions. You certainly don't catch many tench with the snuffles. Whether this is because of its natural slime or some mysterious built-in aspirin is not clear. More interesting to the fisherman is the tench's ability to survive in conditions that would kill any other fish. If tench are dying, don't drink the water.

They can also hang on in when waters start to dry up. As long as there is damp mud, tench will bury themselves and wait for better (or wetter) days. They live happily in mud and much of their food is filtered from it, so it is no surprise to find that their usual shade is an unexciting brown, the colour of old hospital tiles. It is probably a good camouflage, though I'm told gypsies used to catch tench with hay rakes from farm ponds.

A rake would certainly have been easier. My nice new net looks as if it has been catching alligators. The only way to rescue the tench, apart from wading waist- deep, was to scoop out a netful of mud and rootle through it to find the fish. This activity stirred other dormant tench to life and I caught four, all about 3lb. There may have been more but the pond looked as if a JCB dance party had been held there when I'd finished. The tench are now in the Ouse, where for the moment at least, there is plenty of water. They'll probably hate it.