▷ Velvet disease in fish | Details, diagnosis and treatment

external symptoms

Behave

photos

Photo: Reiner

Scalar, probably with velvet disease

Photo: EisenStern

The picture shows a discus in which the detection of the disease was not easy. At first I guessed a fungal infection, because apart from the dark coloration of the fish, nothing else could be seen (which would have been described). Two other discs showed whitish discolouration on the skin.

The following were noticeable: – clear, slightly milky threads which the fish pulled behind it coming from the skin, the gills and later also from the mouth. – difficult breathing – discoloration of two other discs in the basin – milky-slimy deposits on the discs – water surface as if wet with protein (streaks)

After the fungus treatment didn’t work, I filtered over activated charcoal for 24 hours. In the morning (after the 24 h) all the fish in the tank (including catfish) stayed close to the water (and air) inlet. Immediately carried out a very large water change (although the last partial water change was only 3 days ago) and off to the specialist trade.

They didn’t know what to do there either, so I took Tetra’s «General Tonic» with me, which I put in high doses in the pool.

I am now certain that it was the velvet disease – which can also be treated with the tonic. Unfortunately, the discus mentioned above did not survive the day and an examination of the gills revealed no infestation by parasites, but total congestion, so that the animal was obviously no longer able to exchange oxygen.

The thickened gill cover can be clearly seen in the picture, which the discus could no longer open completely. Also easy to see: the pinched pectoral fins.

Another tip: the dots on the skin and fins (see external symptoms) look as if “air bubbles” had settled on the skin.

(Comment by EisenStern)

Photo: Janine Klaus

Malawi cichlid with velvet disease.

causes

The velvet disease is also known under the name Oodinium. However, the correct name has been Piscinoodinium for some time, as the scientific name of the pathogen was changed from Oodinium pillularis to Piscinoodinium.

Piscinoodinium is a dinoflagellate that can grow to 0.1 mm. It is therefore significantly smaller than the causative agent of white spot disease. Since the pathogens of the velvet disease often appear in clusters together in clusters, the two diseases can still be easily confused. A fish suffering from velvet disease appears to be covered in fine gold dust. Often the coating can only be seen if you look at the fish lengthways against the light, or at night in the light of a flashlight in an otherwise dark aquarium. The covering has a velvety effect when the infestation is severe and thus gave the disease its name.

The coating is difficult to see with normal aquarium lighting. Sometimes it helps to turn off the lights, darken the room completely and shine a flashlight on the fish from behind if possible. Often the disease first becomes visible at the gill openings or at the base of a fin. Later, the eyes can also be affected.

Fish that have been infested for a long time can get dark head or back.

The velvet disease is often only recognized when the infected fish is lying on its side on the bottom and desperately trying to get to the water surface to gasp for air. Then it is usually too late for successful treatment. However, a quick response can potentially save the lives of other fish. Without treatment, many fish can die from velvet disease within a short period of time.

The parasitic pathogen has root-shaped plasma filaments with which it anchors itself in the skin, fins or gills of the infected fish. The pathogens can also enter the intestines and stomach through the mouth and get stuck there. The skin of the fish is destroyed by the clawing. Since the pathogens often attach themselves to the skin in groups, it is possible that the damaged fish cells release substances that attract more dinosaur spores. If the infestation is severe, the resulting wounds can also be attacked by bacteria, resulting in diseases such as fin rot and inflamed, red spots. The inflammation can cause larger areas of skin to peel off.

The pathogen absorbs part of its nutrition from the skin cells of the fish by osmosis. In contrast to the causative agent of the seawater oodinium disease, the causative agent of freshwater oodinium only partially feeds on the contents of the skin cells by dissolving them. It also nourishes itself through photosynthesis.

The pathogen has chloroplasts that perform photosynthesis and supplement the nutrients ingested by the fish. Yellow and brown carotenes are mixed with the green chlorophyll. This gives the rubber its typical brown-yellow color.

The pathogen can also release nutrients from the cells of the gills. The gills secrete mucus and swell. If the infestation is severe, the gill cover may look swollen.

After 3 to 7 days, the pathogen, also called trophont, has received enough food and is adult. During this time it has increased 5 to 6 times. He detaches from the fish, swells and falls to the bottom. A spherical cyst forms there in which the pathogen divides. As a result of repeated division of the daughter cells, up to 256 spores are finally formed. These spores each form 2 visible flagella and are therefore flagellates. Only one of these flagella is used for locomotion and protrudes from the cell. Under the microscope you can see that the spores are almost round and the two flagella are located at the intersection of a longitudinal and a transverse furrow. You can also see a red eyespot. When the spores leave the cyst after three to five days, they are called dinospores or swarmers. Without a host, the dinosaur spores can survive for about 24 hours, otherwise they die. However, it is suspected that the dinosaur spores can even survive for several days without a host. Once the dinospores have found a new host, they form their root-like plasma filaments and anchor themselves in the fish skin. While free-swimming, the pathogens carry out photosynthesis. A complete life cycle takes 10 to 14 days at aquarium temperatures. Other sources speak of 14 days with optimal temperatures between 23° and 26° C.

While young fish in particular can die quickly from the bacterial sequelae, the actual velvet disease often lasts for a few weeks until the skin is so badly infested with pathogens that it peels off and the fish slowly die. If only the gills are affected, the affected fish can even die without any obvious external symptoms of velvet disease. The velvet disease is even more dangerous because the pathogens can also settle in the intestines of the fish, where they are protected from medication.

The velvet disease mainly affects killifish, labyrinth fish, rainbow fish and barbel. But many other fish species are also affected, with live-bearing and Malawi cichlids being affected only rarely. Young fish in particular fall victim to velvet disease, while older fish appear to be able to acquire some form of immunity.

Damage to the gills cannot always be healed, even if the fish survives the disease. As a result, surviving fish may gasp for the rest of their lives.

treatment suggestions

Special remedies are available to treat velvet disease. These agents usually contain copper, which can be harmful and even fatal to some aquarium inhabitants, e.g. B. catfish, shrimp and snails. Since agents with malachite green, e.g. E.g. remedies against white spot disease or broad-spectrum remedies against the parasites of velvet disease should be avoided if necessary. Longer salt baths with 2 to 5 milligrams of salt per liter of water or an increase in temperature are also suitable if the affected fish can tolerate them . If the infestation is severe, simultaneous treatment against bacterial infections can be useful.

It may be helpful to keep the aquarium dark during treatment, as darkness prevents photosynthesis of the pathogens and slows down the development of the dinospores. However, darkness alone probably does not kill the pathogens.

Since the velvet disease usually comes into the aquarium with new fish and can then lead to serious problems due to the rapid development, new fish should be born in 3 to 4 weeks Quarantine being held.

Further information