[FluffynTex]

I googled it and found the following info....

Leeches are parasite that are easy to spot and identify as they tend to be large enough to be spotted with the naked eye. Leeches are worms that often appear hearth shaped as they curle themselves toward the body of the fish. Leeches attached themselves onto the body, fins or gills. Leeches can only be found in your aquarium if you have introduced them to your aquarium somehow. The main way to introduce leeches is with live food that has been caught in leech infested waters. Refraining from feeding live food you have not cultivated yourself and especial wild caught live food will dramatically reduce the risk of getting leeches in your aquarium. Leeches can also be introduced with new fish and plants. You should therefore carefully examine new fish and the water in the bag for leeches before letting the fish into you aquarium. Ideally you should also keep the new fish quarantined for a while to prevent introducing other diseases. Plants should also be inspected to avoid introducing leeches, and to be extra safe you can place new plants in a 5 mg/l potassium permanganate solution for about an hour before adding them to your aquarium. The potassium permanganate will kill any leeches that might hide among the plants in question.

It might be tempting to get a pair of pliers and manually remove the leeches from you fish but you should never do that. This is due to the fact that the leeches borrow themselves into the surface of the fish and forcibly removing them can cause serious damage to the fish. You should instead bath the fish for 12-15 minutes in a 2.5% salt solution. This will most likely cause the leech to release its grip on the fish and if it doesn't, it should at least have loosened it enough for you to be able to remove it using pliers without damaging the fish seriously. Never use this method on salt sensitive fish such as rays and certain catfish species. For salt sensitive species or if you prefer to medicate your entire tank (to make sure to remove all leeches) I recommend adding 0.25 mg Trichlorofon for every litre water in your aquarium If you choose to treat the entire tank I recommend digging up your plants and using the earlier mentioned method to kill any leeches that might be hiding.