What is Amyloodinium?

[snorvich]

What is Amyloodinium?

Velvet or Coral Fish Disease is caused by the dinoflagellate Amyloodinium ocellatum. Oodinium is an older name for this genus, so it often appears in the literature as well. The life cycle of A. ocellatum is very similar to the life cycle of marine ich (Cyrptocaryon irritans). This organism is parasitic on fish at one stage in its life cycle; during that stage it is visible to the naked eye. The total life cycle for this parasite is about 3 weeks; but for total safety, after a tank is infected, it should be kept fish-free for 6 weeks. This disease is very similar to marine ich but the effect on fish is much more severe.

Because this organism is able to reproduce so rapidly, when an Amyloodinum outbreak occurs in an aquarium, it can reach disastrous numbers in a very short period of time. This parasite is one of the most common causes of a tank wipeout, or an abrupt loss of all the fish in a saltwater aquarium. By the time you notice the problem it often is too late.

The Life Cycle of Amyloodinium ocellatum

• Free-swimming cells called dinospores are released from a mature cyst and go in search of a host fish. Typically these cells can survive seven to eight days without a host, but at temperatures around 75-80 degrees, some strains may last up to 30 days or more. Raising the temperature will speed up the lifecycle but it also reduces dissolved oxygen in your tank water. For fish with this parasite in their gills, this treatment can be dangerous.

• Once a host is found, typically heading for the soft tissue inside the gills first, the dinospores lose their swimming capabilities and become non-motile parasitic trophozoites. At this stage they turn parasitic, as each attaches to the host fish by sending out a filament for feeding.

• After feeding for 3 days to a week, the trophozoites become mature and either drop off into the substrate, remain hidden in the mucous membrane, or sometimes remain deeply embedded in the tissue of a host fish. At this point, each forms a hard shell covering.

• Inside each encrusted cyst, the cells, now called tomonts, reproduce internally by non-sexual division. Upon reaching maturity in about five days, each cyst ruptures and releases hundreds of new free-swimming dinospores to start the cycle all over again, but in much large numbers.

Symptoms

Much like Brooklynella, Amyloodinium organisms primarily attack the gills first. At the onset of this infestation, fish often scrape up against objects in the aquarium, become lethargic, and start respiring rapidly, which is the result of damage to the gills caused by the parasites. This is typically noticed as fish staying at the surface of the water, or remaining in a position where a steady flow of water is present in the aquarium, such as near overflows or powerheads.

As the disease progresses, the cysts become visible on the fins and body. Although these cysts may appear as tiny white dots the size of a grain of salt, like the first sign of marine ich, Amyloodinium also causes the fish to have the appearance of being coated with what looks like a whitish or tan to golden colored, velvet-like film, thus the name Velvet Disease.

In the advanced stage of the disease, the production of gill and body mucus increases and the fish becomes listless, refuses to eat, and sometimes develops secondary infections. Fish that reach this end stage of the disease usually do not respond to treatment, and most often will die.

Most Effective Treatments for Amyloodinium

• Remove all fish from the main aquarium and give them a freshwater dip. For this dip, adjust the pH and add Methylene Blue (at double the in-tank concentration). Use a specific gravity of 1.001 for the saltwater fish. This dip should be no less than 3 minutes and no more than 5 minutes to be effective. This is very effective in removing Amyloodinium directly from the fish (including gills). Do not be alarmed if the fish ‘lies down’ and acts dead; this is a common initial reaction and the fish will usually perk up a minute or two into the dip. The cell membrane of the Amyloodinium cyst cannot withstand the change in osmotic pressure as well as the fish and will burst, that is why the minimum three minutes is a must. This dip is more effective for Amyloodinium than marine ich because the Amyloodinium cyst does not imbed as deeply as the marine ich parasite does.

Following a fresh water dip, use a formalin bath, and then place them in a QT with vigorous aeration provided. To address complications from secondary infections, also treat the fish with an appropriate antibiotic or anti-bacterial medication. Continue treating the fish in the QT until the Amyloodinium appears to be gone, and then keep treating for another week after that.

• Unfortunately, Amyloodinium can withstand a broad salinity range (from 3 to 45 ppt) so hyposalinity is not an effective treatment.

• Many sources recommend treatment with copper, however, keeping copper at the proper level is very difficult and infeasible for most aquarists, which is why many prefer a freshwater dip followed by a formalin bath.

• Chloroquine diphosphate is a very effective (probably the most effective) treatment for Amyloodinium. Use a single dose of 10mg/l and leave the fish in the tank for 20 days.

Preventing Reinfection

Reinfection will occur no matter how effectively the fish have been treated if the Amyloodinium organisms are not eradicated from the main aquarium. Because they require a fish host to survive, keeping the tank devoid of any fish for at least six weeks will remove the parasite. For fish-only aquariums the tank temperature can be elevated to 85 to 90 degrees to speed up the life cycle of the organisms, which will help to eliminate all cysts and dinospores in three weeks.

[snorvich]

"Infective dinospores can be transported in aerosolized water droplets (Roberts-Thompson et al 2006). Droplets from static systems were shown to be transmissible for up to 1.44 feet however droplets from dynamic ones were shown to be transmissible up to 9.8 feet. This means that adjacent aquaria, (and potentially ponds), could spread the infection of parasites such as cryptocaryon irritans, amlyloodinium, etc. to other aquaria nearby. As such that aquaria that are situated close together should be covered especially if one is known to have or have had a parasite." These references were originally from Fish Disease: Diagnosis and Treatment By Edward J. Noga but after additional use of Google Scholar, there were other examples. So bottom line is respect aerosol transmission of parasites between proximate aquaria.