A Fisherman in the desert

The appeal of catching tiddlers is almost instinctive I think and sweeping my net through the brown water I caught three fish on my first attempt. The two females and a male were just right for my purposes. I wanted to get some photos and also to try keeping them. I popped my new pets in a large jam jar I had brought with me.

I took a look at my captures and also at the pools where I caught them. There is something very primeval about the place, with the volcanic rubble of the surrounding area, the slimy stinking and bubbling mud, and predatory insects like the large red dragonflies whose ancestors date back to prehistoric times.

There are actually several species known as Mosquito Fish, but Gambusia affinis and Gambusia holbrooki are the main ones that deserve this name. They originally came from Mexico and the central and southern states of America, but have been introduced into tropical and subtropical fresh water all over the world to help eradicate the biting pests they are named after.

Mosquitoes breed in shallow stagnant water and these little fish greedily snap up the wriggling larvae. One large female fish can eat up to 200 larvae in a day.

Both Mosquito Fish and Guppies have been added to reservoirs and irrigation tanks in some parts of Tenerife and the Canary Islands, as well as being kept in ornamental pools. I tried keeping my Mosquito Fish in a large 5 litre plastic bottle and found they seem happy enough on a diet of tiny scraps of cat-food. They also love the little green caterpillars that were ruining my houseplants.

Mosquito Fish are remarkably tolerant of their conditions and can live in fresh or brackish water and take temperatures up to 100 degrees Fahrenheit.

However, their use as a pest-control agent has its limitations and potential problems. Although they do fine at eating mosquito larvae in water troughs, irrigation tanks and disused swimming pools, in natural ponds and lakes they can pose a threat to native aquatic life like fish fry and tadpoles. This is why some conservationists call them "Dambusia" instead of Gambusia.

Damned mosquitoes aren't fussy, about whom they bite, where they breed or where they carry disease. They lay their eggs in any stagnant water they can find and often this may well be an old bucket or other container. In situations like these, Mosquito Fish are clearly of no use in keeping numbers of the larvae down.