Argulus / Fish lice
Argulus, also known as fish lice, is a crustacean parasite that will attach to the fish using curved hooks and suckers. This parasite has a direct life cycle and will only infest fish. Mating takes place during the free-swimming stage of the lifecycle and egg clusters are released in the aquarium. After being hatched, the parasite must find a suitable host within four days, otherwise it will die. The whole life cycle takes between 30-100 days depending on water temperature.
When the parasite has attached itself to a fish, it will insert its needle-shaped mouth into the tissue. This parasite causes patches of swollen and bleeding skin and can affect the entire body, including fins and gills. It feeds on blood and other bodily fluids, and it causes further harm to the fish by injecting digestive enzymes that can lead to systemic illness. It is sometimes possible to see the parasite with a naked eye because this oval, flat parasite can reach a length of 10 mm. Other symptoms are small dark spots on the skin, typically behind the fins and around the head. Affect fish are known to clam their fins and scratch themselves against rough surfaces in the aquarium.
A 10-30 minute long potassium permanganate bath (10 mg potassium permanganate per litre water) is usually enough to kill the argulus parasite. In some situations, you have to treat the entire aquarium to get rid of them by adding 2 mg potassium permanganate per litre. It is possible to pick off the parasite from the fish with a pair of forceps, but it can be tricky to find all the parasites and remove them.
Does anything described above relate to your fish and tank? If you are unsure... maybe catch a few of them in a bag and take them to you LFS? I know that there are different treatments out there to deal with parasite infections... I just don't know the name of any because I haven't had to use it for my fish.
I hope that helps you out a bit... maybe see if anyone else has any more ideas
