Velvet disease (also called gold-dust, rust and coral disease) is a fish disease caused by

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

parasites of the

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

'' Amyloodinium'' in marine fish, and ''

Oodinium ''Oodinium'' is a genus of parasitic dinoflagellates. Their hosts are salt- and fresh-water fish, causing a type of fish velvet disease (also called gold dust disease). One species has also been recorded on various cnidarians. The host typical ...

'' in freshwater fish. The disease gives infected organisms a dusty, brownish-gold color. The disease occurs most commonly in tropical fish, and to a lesser extent, marine aquaria.

Life cycle

The single-celled parasite's life cycle can be divided into three major phases. First, as a

tomont Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism i ...

, the parasite rests at the water's floor and divides into as many as 256 tomites. Second, these juvenile,

motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

tomites swim about in search of a fish host, meanwhile using

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

to grow, and to fuel their search. Finally, the adolescent tomite finds and enters the slime coat of a host fish, dissolving and consuming the host's cells, and needing only three days to reach full maturity before detaching to become a tomont once more.

Pathology

Velvet (in an aquarium environment) is usually spread by contaminated tanks, fish, and tools (such as nets or testing supplies). There are also rare reports of frozen live foods (such as bloodworms) containing dormant forms of the species. Frequently, however, the parasite is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to a fish, and only causes a noticeable "outbreak" after the fish's immune system is compromised for some other reason. The disease is highly contagious and can prove fatal to fish.

Symptoms

Initially, infected fish are known to "flash", or sporadically dart from one end of an aquarium to another, scratching against objects in order to relieve their discomfort. They will also "clamp" their fins very close to their body, and exhibit

lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...

. If untreated, a 'dusting' of particles (which are in fact the parasites) will be seen all over the infected fish, ranging in color from brown to gold to green. In the most advanced stages, fish will have difficulty respiring, will often refuse food, and will eventually die of hypoxia due to

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

of their gill tissue.

Treatment

Sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...

(table/sea salt) is believed to mitigate the reproduction of velvet in freshwater fish, however this treatment is not itself sufficient for the complete eradication of an outbreak. Additionally, one of the common medications designed to combat the disease must be added directly to the fish's environment. These medications usually include the active ingredients

copper sulfate Copper sulfate may refer to: * Copper(II) sulfate, CuSO4, a common compound used as a fungicide and herbicide * Copper(I) sulfate Copper(I) sulfate, also known as cuprous sulfate, is an inorganic compound with the chemical formula Cu2 SO4. It ...

methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin ...

formalin Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

malachite green Malachite green is an organic compound that is used as a dyestuff and controversially as an antimicrobial in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper. Despite its name the dye is ...

or acriflavin. Additionally, because velvet parasites derive a portion of their energy from

, leaving a tank in total darkness for seven days provides a helpful supplement to chemical curatives. Finally, some enthusiasts recommend raising the water temperature of an infected fish's environment, in order to quicken the life cycle (and subsequent death) of velvet parasites; however this tactic is not practical for all fish, and may induce immunocompromising

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

References

{{fish disease topics Fish diseases Veterinary protozoology

Life cycle

Pathology

Symptoms

Treatment

See also

References