Taking extreme measures to save my fish

RECENTLY I noticed that the fish in my small pond had starting acting oddly.

They were off their food and spent a lot of time hiding in clumps of weed or crevices in the stones. They alternated this reclusive behaviour with occasionally dashing about in a mad fashion and scraping themselves against hard objects.

Something was obviously wrong so I got down on my knees for a closer look. That’s when I noticed a scattering of tiny white spots on their bodies. It looked as if someone had shaken fine grain salt over them.

The condition was remarkably easy to identify with the aid of the internet. It was Ichthyophthirius multifiliis. This is so difficult to spell or pronounce that fish keepers have come up with a number of simpler names – it is often called ‘white spot disease’, ‘ich’ or ‘ick’. It’s caused by a protozoan parasite and is a common complaint in ornamental fish in ponds or aquariums and can break out in freshwater fish farms and sometimes in free-swimming wild populations.

The life cycle of these protozoa is quite interesting. Each little white spot on my poor goldfish is a cyst containing an adult parasite which is actually eating the fish alive. Eventually the cysts break open and produce what, to be rather unscientific about it, amount to baby protozoa. These are free-swimming in the water and can increase by binary fission, splitting in two up to ten times. Each cyst can produce up to 500 microscopic ‘babies’.

The duration of these events depends on water temperature. The entire life-cycle is about a week at 25 degrees but up to 8 weeks at 6 degrees.

The free-swimming ‘babies’ (there are scientific names for them at various stages in their development) spend some of their time clinging on to objects in the water but they have to swim around as well because if they fail to find another host fish and complete their life-cycle they will die within a few days. It’s all a rather desperate business.

All the more desperate because eventually it would probably kill the three goldfish and two shubunkins confined in my little pond.

Luckily there are a number of treatments. The one most commonly recommended for an aquarium or small pond is a chemical called malachite green. This is a synthetic chemical and has no connection with malachite the mineral apart from the fact that they both have an intense green colour. It has an eye-achingly long chemical symbol and was first developed as a dye for fabrics.

Its use to cure fish diseases is controversial and it is now illegal in most countries to use it on fish farms that produce fish for human consumption. There are a few people who eat goldfish but this is quite rare so malachite green is still legal for use with ornamental fish.

So, armed with all this information, I went to the local pet shop and explained the situation. The knowledgeable and helpful owner sold me a bottle of bright green liquid which, although it had a proprietary brand name, was undoubtedly malachite green. It cost more than the fish but I was determined to give it a go.

After some complicated mathematics to work out how many litres of water I had in my pond, I applied the chemical to the water, which immediately went dark green, in two doses four days apart. So far I can see some improvement but not a complete cure and I’m a bit concerned about the ecological impact of the treatment on other creatures living in the water. But I may have to go back and buy another bottle of malachite green.

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