fish lice

Symptoms: Behavior wise, you will see the fish trying to scratch itself against anything it can find. You will also see round-shaped transparent parasites attached to the body of the fish. There may be red or scarred areas where the parasite has been before.

Reason: These parasites, which have eight legs, are lice (Argulus) that attach themselves by suckers, break the skin and feed on fish. The eggs are laid away from the fish. Some say they are often mistaken for algae but if you look closely enough you will see what they are if they are adults as they appear green in colour, but the young ones may not be as obvious.

Treatment: Adult parasites can be removed with tweezers once the fish has been removed from the aquarium. Treat the affected area with an antiseptic. Then you could use a whole tank treatment to deal with the younger, newborn parasites with an organophosphate like Dimlin (Diflubenzuron), but this type of chemical is now banned in many countries.

I have noticed that Parazin P has been proposed, a suitable drug to treat crustacean infestations, which takes several weeks to take effect as it is based on the life cycle of the parasite.

I have also read about a treatment in which the fish is rubbed with a roll of kitchen paper on the area affected by the parasite, the fish is submerged in water (at the same temperature as the main tank) and all the parasites in that area come out of the fish! Parasites apparently don’t like dry conditions, hence the use of the dry paper roll. It can’t do any harm, so why not give it a try?

Fungus

Symptoms: The areas of the body that are affected are those in which the mucous layer that protects the skin has been damaged. You will see a cotton-like material attached to the fish or the entire appearance of the skin may appear dirty. You can see why it is also called the cotton disease. The types of fungi are typically Saprolegnia, Achlya, Leptomitus, and Pythium.

Reason: This is a secondary infection as it often occurs after an initial wound has occurred or when a parasite has been active or after the fish has suffered a white spot. It can also be due to poor water quality.

Treatment: You can use a proprietary fungicide like phenoxyethanol to treat individual fish in a hospital/quarantine tank, but try to determine the cause of the outbreak and take corrective action, otherwise it may come back. Salt baths are another alternative or the use of Gentian Violet topically on the affected area.

Gil Flukes (Dactylogyrus)

Symptoms: You will see the fish rubbing against objects to relieve the itch. It may be breathing fast or swallowing oxygen at the surface. As the disease takes hold, the fish will become lethargic and try to isolate itself in a corner or stay at the bottom of the tank. It will stop eating, have swollen gills, and one gill may stay open or closed.

Reason: A worm-like parasite up to 2 mm long infests the gills of fish and reproduces there. It has hooks on its body to dig into meat, causing damage and possible bacterial infection. But the main effect is to reduce the fish’s ability to breathe and get enough oxygen, which eventually leads to their death.

Treatment: This is an infectious disease so treatment of all fish is recommended. Since the eggs of the parasite are quite resistant, repeated treatments will be needed for a few weeks to kill the newly hatched worms. Fluke tabs are no longer recommended.

Praziquantel (Droncit (US) or Drontal (UK) are preferred as they are safer for fish. Other UK treatments include Paragon (for mild infections and safe with shrimp and snails) or Sterazin (for severe infections but not safe with shrimp and snails.) A follow-up bacterial treatment is probably advisable to counteract any secondary infection caused by the parasite.

Hole in the head (hexamithiasis)

Symptoms: As the disease can affect both the intestines and under the skin, you may see stringy white feces and literally holes in the poor fish’s head. Discus are particularly susceptible. You can see the fish swimming backwards, its color may darken, and it may hide, head down.

Reason: A parasite called Hexamite is the culprit. It lives in the intestines and can become a problem when fish become stressed and/or weakened due to poor environmental conditions.

Treatment: Metronidazole at approximately 500 mg per 10 gallons is the normal dose. First dissolve the medicine in hot water. Multiple treatments may be needed over two weeks with 50 percent water changes before each treatment. I have noticed that some people add Malachite Green to work on secondary infections.

Since the disease is also internal, it is also appropriate to medicate the fish with food. 250mg (0.25g) of metronidazole in 25g of food will do the trick.