What causes amyloodiniosis?

Amyloodiniosis is caused by a dinoflagellate parasite called Amyloodinium ocellatum. The parasite infects both elasmobranchs (sharks and rays) and teleosts (bony fish) (Noga and Levy, 1995).

The life cycle of A. ocellatum

A. ocellatum has a three-stage life cycle: parasitic trophonts, encysted reproductive tomonts and free-swimming infective dinospores. The parasitic trophont attaches to the one or more epithelial cells via rhizoids. It appears that nutrients are absorbed via the rhizoids. After the trophont matures, it detaches from the host, retracts it rhizoids, forms a cyst and becomes a tomont. The tomont may divide up to 8 times producing 256 dinospores (Noga and Levy, 1995). The free-swimming dinospores seek out a fish host to infect and remain infective for at least 6 days at 26°C (Noga and Levy, 1995). Amyloodinium can complete its life cycle in under one week under optimal conditions (Noga and Levy, 1995).

Signs of amyloodiniosis

The signs of amyloodiniosis include respiratory difficulties, loss of appetite, swimming near the surface, scratching. As the gills are usually the primary site of infection, difficulty in breathing is the most common sign and may be the only sign before death. Heavy infections may also affect the skin, fins and eyes. The common name "marine velvet" comes from heavy infestations of the skin which may have a dusty appearance.

Mild infestations of 1 or 2 trophonts per gill filament cause few problems, however heavy infestations of up to 200 trophonts per gill filament cause severe damage to the gills, including inflammation, haemorrhage and tissue death. The fish usually die from a lack of oxygen within 12 hours of a heavy infestation. (Noga and Levy, 1995). Given the short life cycle, a mild infestation can become a heavy infestation in under a week.

Treatment for of amyloodiniosis

Chemotherapy is the only effective treatment for Amyloodinium, with copper being the most widely used. Copper will not affect trophonts or tomonts but is toxic to the dinospores (Noga and Levy, 1995). Free copper should be kept at 0.12-0.15 mg/L for at least 14 days, although 21 days is better to be certain of killing all dinospores and to ensure that all trophonts have become tomonts and all tomonts have excysted. Copper cannot be used in the presence of invertebrates and treatment should be performed in a hospital tank void of any calcium carbonate substrate. The copper level needs to be tested regularly to ensure that sufficient concentrations are maintained. Copper is also toxic to the fish and care must be taken to avoid overdose.

Of all the copper medications available on the market, Cupramine by Seachem appears to be the safest. It is a complexed copper and is more stable that copper sulfate, copper citrate or chelated copper. As it is complexed, the total copper concentration should be maintained at 0.5 mg/L for three weeks.

Noga and Levy (1995) report on success with the use of chloroquine diphosphate (an antimalarial medicine). It was found to be very safe and effective in killing dinospores on excystment. It is non-toxic to fish, but very toxic to algae and many invertebrates, so, like copper, should only be used in an hospital tank. Treatment involves maintaining chloroquine diphosphate at 5-10 mg/L for 10 days.

Freshwater dips of a duration of around three minutes can dislodge most but not all trophonts, offering temporary relief to the fish. Additionally, this feature can be used to determine if fish are infected with Amyloodinium. See: oama's Freshwater Dip Test.

Prevention of amyloodiniosis

Prevention of Amyloodinium in display tanks is best achieved by quarantining all new fish for at least 20 days. If the parasite is present it on the new fish there is an extremely high probability that the fish will show signs before 20 days, which represents 2-4 complete cycles of the parasite.

Further reading

Getting Acquainted with Amyloodinium ocellatum
Amyloodinium Infections of Marine Fish.

References

Noga E.J. and Levy M.G. 1995. Dinoflagellida (Phylum Sarcomastigophora) In: P T K Woo (ed.) Fish Diseases and Disorders. Volume 1: Protozoan and Metazoan Infections. CAB International, Wallingford, Oxon. pp 1-25.

Last updated: February 11, 2004