Aquarium tropical fish and fish diseases




Latin name: Oodinium
Other names: Coral Fish Disease
Pathogen: parasite

Symptoms: Microscopic examination of skin and fins scrape shows parasites, Through the magnifying glass it can be observed that scales have small goldish bumps on their edges, which can turn into continuous coating in bad cases, Fish hide in secluded places, Fish itch (fish scratch on the rocks and other objects), Entire body covered whith gray coating, Fins stick together, Separation of fin rays, Skin detaching, Velvety coating

Affected fish rub against hard objects and plants, hang in the corners of the aquarium. Fine yellow or grey film appears on the skin, fins are held to the body, inter-ray tissue disintegrates, the skin peels away. Through the magnifying glass it can be observed that scales have small goldish bumps on their edges. In cases of extensive infestation they look like a coating. Microscopic examination of scrapings of the skin and fins will show parasites.

Velvet disease is a fish disease caused by the dinoflagellate parasites of the Class Flagellata. In freshwater fish Velvet is caused by either Oodinium pilularis or Oodinium limneticum, in marine fish by Oodinium ocellatum also known as Branchiophilus maris. The flagellated have different biological and morphological characteristics. Oodinium is special kind of protozoa as it is a plant unit. Oodinium is a dinoflagellate, a single-celled organism that appears as a pear-shaped golden-brown cell, 125-130 micrometers in length. It is covered by cilia and has two flagella, one of which is much longer than the other. Inside, there is a nucleus, about 12 micrometers in diameter.
Flagella and celia propel the parasite through the water. The parasite finds a fish and adheres using flagella. It then breaks through the epithelium, fins, gill filaments as well as through the mucous membrane in the mouth. The parasite does not form pseudopodobia. It grows under the skin and later (depending on water temperature) leaves its host. It usually happens on the 3rd or 4th day at water temperatures of 23 to 25C (73-77F). At lower temperatures, the parasite can stay on the host longer. An increase in temperature can cause the parasite to stay on the fish for 2 or 3 days more. When the mature parasite leaves the host, it drops to the bottom of the aquarium or plants. Here it forms a cyst (a sack that enables it to survive adverse conditions). This stage is called palmella. The cyst divides forming between 34 and 64 new cells where upon the membrane bursts freeing the cells into the aquarium. The free-swimming organism is called a dinospore. A dinospore has two flagella, one of which is covered by a body fold and has a reddish eye. Cilia and flagella propel a dinaspore through the water. When it attaches to the fish, the life cycle starts all over again. Temperatures and water pH as well the lightning influence the duration of the parasites life cycle. Water temperatures between 23 and 25C (77F), pH of about 7 and bright lightning are optimal for the parasite. In such conditions, the life cycle of the flagellate usually takes between 6 and 8 days. Dinospores become even more active if temperatures are raised above 26C (79F) and lightning gets brighter. At the same time, its free-swimming stage (before it finds a host) becomes considerably shorter (about 24 hours).
Oodinium limneticum. It is an oval-shaped parasite, whose body is divided into two by a burrow , which gives the impression that the parasite consists of two halves. The parasites uses its two flagella (one of which is considerably longer than the other one) to propel itself in the water as well as to attach oneself to the fish. Preudopodobia also serve as means of attachment. The organism contains chlorophyll which gives the parasite its typical gold or rust color and enables it to produce its own food. Unlike Oodinium pillularis and Ichthyophthirius multifiliis, Oodinium limneticum does not eat into the cells of the epithelial layer of the skin and fins, but localizes right on their surface. It multiplies on the host rather than at the bottom of the aquarium or on the plants. The optimum temperature for reproduction of Oodinium limneticum is 22-26C (72-79F). Once on a host, the parasite encysts, then undergoes cell multiplication to form 200 free swimming parasites called dinospore while losing its pseudopodobia. The whole process takes between 4 and 5 days. Then the cyst bursts freeing dinospores into the aquarium to find a new host. All chlorophyll that a dinospore contains is used within 3 days and it dies unless a new host is found. Once on a host, dinospores burrow into the epithelial layer of the skin and fins and the life cycles begins all over again. The full life cycle takes on average between 8 and 10 days. At temperatures below 22C (72F) and above 26C (79F) parasites multiply more rapidly. Of course, such hydrochemical characteristics as lightening, pH, and water hardness influence the life cycle of the parasite, but these issues have not been studies well yet. A fish-breeder might get confused by the fact that sick fish do not lose appetite until their death. Parasites that damage the epithelial layer of the skin and fins cause excessive mucous production and disrupt gas exchange in the skin. The latter is particularly dangerous for young fish whose gill apparatus is not yet well-developed and oxygen enrichment of blood is carried out mainly though the skin. Oodinium pillularis is most damaging to fish. The abovementioned clinical signs of Oodinium are not always well-pronounced, especially in adult fish. It is not uncommon for aquarists to confuse Oodinium and Ich. That is why microscopic examinations are particularly important.
According to some foreign scientists, in the event of reinfection parasites infect previous sites of attachment and fish become immune to the disease and become only carriers. They also believe that no deaths in the case of reinfection have been observed so far. Results of research carried out by Russian scientists speak to the opposite. Lethal outcomes in adult fish that survived Oodinium have been observed on numerous occasions. The reinfection of fish that survived Oodinium (that were absolutely free from the parasite), is not uncommon, especially if caused by Oodinium pillularis, and in the case of severe infestation fish will often die. Thermal and hedrochemical characterists as well as lightening were optimal for the development of the parasite. At the same time, these conditions are also ideal for most species of tropical fish. The selectivity of parasites to the place of attachment is explained by the degree of regeneration of affected organs and tissues as well as the period of time that passed between recovery and reinfestation. Clinical signs are not sufficient to make the final diagnosis, as they resemble those of Ich. This is what aquarists who are not specialists in fish diseases should always bear in mind. However, a thorough analysis of clinical signs is the primary method of establishing a preliminary diagnosis. Good results will be achieved by studying a fish through a magnifying glass. Scales will be covered by tiny golden-brown bumps. Sometimes these bumps will look like a coating which is indicative of severe infestation. It is often impossible to see this with the naked eye. The final diagnosis should be based on clinical signs, epizootological data and microscopic examinations of scraping of the skin and fins. Microscopic examination of the gill apparatus is not necessary as parasites will mainly infest the skin and fins. The species of the parasite does not play the key role in the choice of treatment.

How to cure:
The fact that Oodinium limneticum, unlike Oodinium pillularis, attacks the fishs skin and fins rather than burrows under their epithelial layer, caused some scientists to believe that Oodinium limneticum is easier to deal with and therefore the course of treatment can be shortened. We strongly disagree. One should bear in mind that the life cycle of the parasite included the palmella stage. On living the host, the parasite encysts and lies dormant for a period of time which depends on water temperatures. While in the cyst, the parasite is immune to medications. Finally, the cyst ruptures and releases dinaspores. Treatment is aimed at this free swimming stage. It also kills the parasites which have infested the outer layer of the skin and fins, but fails to eradicate the parasites that have burrowed into the epithelial layer, e.g. Oodinium pillularis. How much time the latter spends under the epithelial layer depends on water temperatures. That is why it is recommended to create conditions optimal for the parasites growth and multiplication and at the same time use the treatment aimed at dealing with them. It is vital that medication is administered at the moment when the parasite leaves the epithelial layer or the cyst. By not creating the conditions optimal for the parasites growth and multiplication (e.g. by prolonging its life cycle) you risk administering medication at the time when the parasite is protected by the epithelium or cyst. By prolonging the course of treatment, e.g. prolonging the time when medication is administered, you risk poisoning the fish. Since Oodinium is caused by two parasites that have different biological characteristics, it was essential to consider their biological peculiarities and explain how they affect the conditions and length of treatment. Therefore, we emphasize the necessity to consider biological characteristics of the parasites when choosing appropriate course of treatment.

Sick fish can be treated either in the separate or in the main tank. To treat fish in the separate tank, use solutions of Malachite green, Copper sulphate, Bicillin-5, and Basic Violet K.
For treatment in the main tank Bicillin-5 solution and solution of malachite Green and Copper sulphate are used. If fish are treated in a separate tank, the main aquarium is fish-free for 7 to 8 days. Water temperatures are maintained at 2426C (75-79F), bright lightening is provided. Equipment is disinfected. Only then can the fish which have undergone treatment be reintroduced into the aquarium.

Since Oodinium are plant-like, it should not be treated with medications used in the case of infestation by animal-like protozoan.

Sera Oodinopur
Sera Aqutan
During the treatment with sera Oodinopur check the concentration of copper in the water (it should not exceed 0.3 mg/L). All invertebrates should be removed from the aquarium.

Malachite Green
copper sulphate
Bicillin 5
Basic Violet K

Newly purchased fish should be quarantined and given therapeutic baths before being introduced into the aquarium. All fish should be given a good clinical examination on a daily basis. New plants should be disinfected. Equipment and tools should not be shared between several aquaria.

Fish susceptible to the disease/disorder:
Oodinium is one of the most common aquarium fish diseases. Oodinium pillularis and O. Limneticum affect freshwater exotic fish of all ages. Most susceptible are Tanichthys (cardinals), Nothobranchius, Hyphessobrycon, Nannostomus, Puntius, Brachydanio, and Danio as well as from the Cyprinodontidae order and the Anabantidae family (Colisa lalia, Alectrias and Macropodus). Least susceptible are members of the Cichlidae family, though they can be carriers of Oodinium. Fry and juvenile fish are more susceptible to disease that adult fish.