Fish Lice
If you’re fish are infected with fish lice on their bodies they will be easy to spot as they will be clearly visible but there may be hidden lice in areas such as behind the fins. They may look like dark spots and a heavily infested fish will be clearly agitated. They are usually around a centimetre long and attach themselves to the fish by their mouth. They are crustaceans and are related to shrimps and crabs. The fish louse which is a member of the genus Argulus usually affects pond fish more than aquarium fish but may be introduced into your fish tank on infected fish. More common in aquarium fish is the gill louse which is a member of the genus Ergasilus and affects both freshwater and marine fish.
Treatment
For larger fish you can try to use tweezers to remove the parasites. Remedies can be purchased, such as Dimilin, but you should isolate the infected fish in a quarantine tank before use. Preventing infestation is essential by quarantining all newly purchased fish in a seperate tank until you are sure that they are free from any parasites or infections.
Bacterial Fish Diseases
There are a whole range of bacteria that can infect both freshwater and marine fish including Red Spot, Tuberculosis, Gill Disease, Tail Rot & Fin Rot, Cotton Mouth, Dropsy and Scale Protrusion. The most common are Fin Rot and Gill Disease. Some symptoms to look out for include red areas on the skin, swollen abdomens, skin ulcers, pop eyes and raised scales. Fish may move about slowly, or hide in corners. However these symptoms may also be a result of parasites, viruses or poor conditions in the tank so it may not be easy to make a diagnosis.
Treatment
Most of these diseases can be successfully treated using antibiotics added to their food. Use at the rate of about 1% antibiotic in flake or frozen food.
Fish Flukes
These parasites are less harmful than fish lice when in small numbers but can cause problems, even death, if the numbers multiply. They are very small and practically invisible to the human eye. You should suspect flukes if your fish rubs itself against objects, has reddeing of the skin, rotting fins or mucus on it’s body or gills.
Treatment
They are best dealt with by placing the fish in a separate tank containing potassium permanganate at 2mg per litre of water.
White Spot
This disease, also called Ich, is extremely common in fish tanks but is reasonably easy to cure. It is caused by a parasite called Ichthyophthirius multifiliis which is a protozoa with a three phase life cycle. These stages are a free swimming phase, an cyst phase and the adult phase and it is only at the free swimming stage that the parasite is easy to destroy. Ich causes problems with breathing, loss of appetite, lethargy and slime on the body. You will also see small white nodules on the fins or body and the fish will rub themselves on objects to relieve the irritation.
Treatment
Treatment needs to be carried out over some time to make sure that all the infestation is dealt with. The whole cycle is faster at a higher temperature so it is best to raise the temperature on the tank to around 80F while carrying out the treatment. Quinine hydrochloride or quinine sulphate can be used at the rate of 30mg per litre of water. Commercial preparations containing copper and malachite green are also effective.
Symptoms: Salt-like specks on the body/fins. Excessive slime. Problems breathing (ich invades the gills), clamped fins, loss of appetite.
Image by Sue Waters

