Trichodina

Photo © Lee Harrell and Mark Strom,
Northwest Fisheries Science Center, NOAA Fisheries Service, USA.
For a larger view click here

by Karen Paul

Trichodina is a microscopic protozoan parasite measuring 50 - 100µm in diameter. Trichodina is only visible under a microscope and is easily identifiable. It looks like a tiny spinning flying saucer from the side. The marine Trichodina is more bowl-shaped as can be seen in the photo above. When viewed from the top the three concentric rings can be seen. The inner denticulate ring, or corona, is composed of hook-like structures called denticles. The middle ring is known as the striated band and overlaps the hooks of the denticulate ring. The outer ring is composed of a thin flexible membrane with a border of cilia.

Symptoms

As Trichodina cannot be seen with the naked eye, the only visible sign of it's presence is that the fish take on a milky appearance due to an increase in mucus secretion. Fish react to Trichodina in the same way as they do to other parasites by flashing and rubbing to relieve the irritation. There are a number of parasites that cause the same symptoms so the only way to make a definite diagnosis is to examine a skin scrape under the microscope. Trichodina does not feed on the fish and is quite harmless at low levels. In large numbers they can be very irritating to the fish and the sucking discs used by Trichodina to attach itself to the fish can cause tissue damage leading to secondary infections. Seriously affected fish may become be lethargic, stop feeding and sit on the bottom with their fins clamped. Severe infestation of the gills can lead to suffocation.

Treatment

Chemical treatments for Trichodina include Formalin, Malachite Green, Chloramine-T and Potassium Permanganate. Any treatment method must take into account the species of fish. Do not use Formalin, Potassium Permanganate or any treatments that state not to be used with Golden Orfe (Leciscus sp.) or Rudd (Scardinius reythrophathalmus) if you have sturgeon in your pond! Chloramine-T or Malachite Green can be used in a pond containing sturgeon but do not use a Malachite and Formalin mixture.

There are a number of proprietary treatments available for the treatment of Trichodina most of which are based on the chemicals mentioned above. Always check the labels to make sure the treatment is suitable for your fish. If in doubt consult a vet. Do not overdose. Chemical treatments are toxic not only to the parasite but also to the fish, especially those already weakened by disease. Always add extra aeration when treating and reduce feed levels.

freshwater trichodinids

Salt can be useful against Trichodina but it will kill plants. Salt should not be used with zeolite filters as it will release ammonia, nitrite etc back into the water. A salt bath can be effective for individual fish.

Large numbers of trichodinids are usually a sign of poor water quality or overcrowding.

As with all parasites and disease, prevention is better than cure. Poor water quality, overcrowding and poor nutrition will cause stress and weaken the immune system. Healthy fish will be able to fight off most diseases and parasites.

Before using any chemical treatments it is advisable to test the water quality. Some symptoms, such as flashing, may be caused by high nitrite levels. Adding chemicals in these circumstances will do more harm than good.

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