Oodinium, Velvet or Coral Fish Disease is a type of saltwater ich caused from an infestation of the dinoflagellate Amyloodinium ocellatum. A member of a large group of flagellate protists that are traditionally subdivided into two groups, the animal-like protozoa and the plant-like algae, Amyloodinium ocellatum belongs to the same group of single-cell alga organisms that cause red tides in marine waters. Although Oodinium does not cause red tides, it is parasitic on fish at one stage in its life cycle, which depending on the temperature of the water can be completed in 6 to 12 days. Being able to reproduce so rapidly, if an outbreak occurs and it is not properly diagnosed and immediately treated, in a closed aquarium system this "disease" can reach overwhelming and disasterous numbers in a very short period of time.
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 in lower tank temperatures at around 75-80 degrees, some strains may last up to 30+ days.
- 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 deriving nutrition for 3 days to a week the trophozoites become mature and drop off into the substrate, may remain hidden in the mucus membrane, or sometimes be deeply imbedded in the tissue of a host fish, where at this point each forms a type of 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.
How Does an Aquarium Become Infected?
- Primarily by not quarantining new fish before introducing them into an aquarium.
- Ocean water, invertebrates, live rock, sand and algae can be carriers of these organisms in any form of their life cycle.
Symptoms to Look For
Most similar symptomatically to Brooklynella, this too is a parasite that primarily attacks the gills first. At the onset fish may scrap up against objects, rapid respiration develops, and fish often gasp for air at the surface as the gills become clogged with excess mucus. As the disease progresses outwards from the gills, the cysts become visible on the fins and surface of the body, appearing as tiny white dots the size of a grain of salt. Fish become lethargic, refuse to eat, colors fade, and mucus production increases. The difference that sets Oodinium apart from Brooklynella at this point is that a whitish, tan to golden colored velvety, powdery or dusty appearance becomes noticable on the fishes body as the cysts proliferate, and it is not uncommon as with all ich diseases for secondary bacterial infections to develop.
Treatment Recommendations
- Remove all exposed fish from the main aquarium and give them a freshwater dip or bath to explode and remove a majority of the parasites, then place them into a QT with vigorous aeration provided.
- Use a copper based medication (shop & compare prices) per the manufacturer's product instructions, and provide treatment in the QT for at least 3 weeks, 4 is better.
- The QT can be treated by hyposalinity or O.S.T. (Osmotic Shock Therapy) alone, or better yet, in combination with the copper medication.
- It is a good idea to treat the fish for or the prevention of complications from secondary infections with an appropriate antibiotic or anti-bacterial medication at the same time.
Preventing Reinfestation
Reinfection will occur no matter how effectively the fish have been treated if oodinium is not eradicated from the main aquarium, which can be accomplished by keeping the tank devoid of any fish for at least 4 weeks. For fish-only aquariums hyposalinity can be applied, and to speed up the life cycle of the organisms, elevate the tank temperature to 85 to 90 degrees, which will help to eliminate all cysts and dinopsores in 3 weeks.
Several days prior to returning the fish to the main aquarium clean all filtering equipment, change any filtering materials, and do a water change.
- ~ Debbie & Stan Hauter
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