This is just one of a number of protozoan that can cause the skin to produce slimy secretions, it is also the most dangerous, albeit the smallest (10-20µ) of the three that I am going to discus here.
Costia necatrix also known as Ichthyobodo necatrix is a bean-shaped flagellate that uses two long and two short flagella for locomotion in its free-swimming state to find a host fish. If the parasite does not find a host within one hour it will die.
When it does find a host it reproduces rapidly and will cover the fish’s body in a matter of days. The parasite can also form cysts, which are highly resistant; this will occur if conditions are unfavourable for the parasite. Once attached to its host’s body, by a suction disc, it feeds on mucus, surface debris and epithelial cells, these are cells that lie just beneath the surface layer of body tissue. This results in damage to the tissues, which causes respiration and mobility problems for the affected fish.
Heavily infected animals may develop reddish coloured patches on the skin, they will swim erratically, glancing their bodies off rocks, or other objects in the aquarium. If the condition goes untreated death will result in end.
If a fish develops sliminess of the skin it may be Costia necatrix, or it may be one of the other protozoans responsible for this condition. The only way one can be certain is by microscopic examination of live skin or gill samples. In general, for tropical aquariums, Costia is not common. It cannot thrive at temperatures above 77ºF (25ºC), and at temperatures above 86ºF (30ºC) it cannot survive at all; it is also more likely to flourish in a crowded aquarium.
If you do encounter Costia necatrix in your aquarium it has the potential to cause substantial damage, it is highly contagious and is the most serious of these parasites, immediate action is necessary. Fortunately, because the survival time away from a host is so short, it is a relatively easy task to rid the aquarium itself of the parasite.
The diseased fishes can be removed to the “hospital” tank, the main aquarium can be left to stand for several hours, which will prove fatal to the parasites, thus getting rid of the problem.
Meanwhile, in the hospital tank, the affected fishes can be bathed in a 1 - 2% salt solution (1.6 - 3.2 ounces per imperial gallon)-(10 - 20g per litre) for 20 minutes; this may be enough in itself to cure the problem. Otherwise, reliable, pre-mixed, ready-to-use medications are available nowadays; as soon as the problem is identified you should seek out the appropriate ready-to-use remedy from your local aquatic store, and follow the manufacturers directions.
See Method of Treatment
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As with Costia necatrix this parasite too causes a slimy skin appearance, the skin and gills may also become discoloured showing bluish-white to grey. Generally, heavy infections can be seen from just behind the head and back to the dorsal. The fish’s swimming will be affected and it will be seen chafing its irritated body against objects in the aquarium.
Chilodonella cyprini is a ciliate of oval shape, its size between 40 and 70µ (1µ [1 micron] = 0.001mm), most of its cilia are arranged in rows along its underside, although it does have a number of larger cilia at one end. It is thought to feed from the epithelial cells and surface debris of fishes, and just like Costia, it dies within a short time, when separated from its host. The parasite reproduces by division whilst on the host fish.
Like Costia, viewing smears under a microscope is the only way to positively identify Chilodonella the smears must be from live fish because the parasite leaves the fish’s body when the fish dies. The symptoms are similar to Costia. When fishes are heavily infested epithelial damage is caused, skin erosion occurs, this may spread to the gills, which affects the fish’s respiration, in severe cases it can prove fatal.
To prevent Chilodonella cyprini form occurring in the first place, avoid overcrowding, as this seems to be the principle cause, especially when new fishes are not quarantined initially.
Treatment is very similar to Costia. A commercial remedy of Malachite Green is effective. Or the affected fishes can be bathed in a 1% salt solution (1.6 ounces per imperial gallon)-(10g per litre) for 10 -20 minutes. Otherwise, reliable, pre-mixed, ready-to-use medications are available nowadays; as soon as the problem is identified you should seek out the appropriate ready-to-use remedy from your local aquatic store, and follow the manufacturers directions. See Method of Treatment
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This is a ciliate protozoan that is generally round or disc-shaped, with a flattened underside, similar to half a sphere. Viewed under a microscope, its underside reveals a suction attachment with a ring of hooks located within it. Once the parasite attaches to its host it continually rotates, and like Costia and Chilodonella, can cause the skin to produce a slimy secretion.
The organism feeds on dead cells and particles caught up in the mucus, and it reproduces by lateral division. There are several species that are known, and it is T. domerguei that is possibly the most common, and probably the least harmful of the three I’ve mentioned here. Unlike Costia and Chilodonella, Trichodina can survive in free-swimming form for up to 24 hours; however, it must find a host within this time or perish.
This parasite rarely causes death, but it can cause irritation and skin damage. It can also spread over the entire body of a fish that may be weakened from another infection. Small infestations are generally not visible, however, if a heavy attack is encountered you may see a grey film over the skin and gills. Common symptoms include gasping for air at the surface and loss of weight.
Apparently long baths are quite effective and a commercial remedy of Malachite Green gives good results. The affected fishes can also be bathed in a 1 - 3% salt solution (1.6 – 4.8 ounces per imperial gallon)-(10 - 30g per litre) for 5 -10 minutes. Otherwise, reliable, pre-mixed, ready-to-use medications are available nowadays; as soon as the problem is identified you should seek out the appropriate ready-to-use remedy from your local aquatic store, and follow the manufacturers directions.