Marine Velvet
Amyloodinium ocellatum
Dinoflagellate Pathogenesis
Marine Velvet is arguably the most destructive and rapidly fatal parasitic disease in marine aquaculture, caused by the parasitic dinoflagellate Amyloodinium ocellatum. Unlike ciliates, Amyloodinium possesses chloroplasts (though non-functional in this parasitic stage) and attaches directly to the host's gill and skin epithelium utilizing highly specialized root-like structures called rhizoids. These rhizoids aggressively penetrate host cells, secreting lytic enzymes that dissolve the cytoplasm, allowing the parasite to absorb the liquefied cellular contents.
The lifecycle mirrors Cryptocaryon but operates at a hyper-accelerated rate. The parasitic trophont feeds for just 2 to 6 days before dropping off as a tomont. Division inside the tomont cyst produces up to 256 dinospores within 2 to 4 days. These dinospores are highly motile, swimming toward light (phototaxis) to intercept hosts in the water column.
Symptoms
Acute Clinical Signs
The velocity of an Amyloodinium infection means fish often perish before dermatological signs are distinctly visible.
- Lethal Asphyxiation: The primary target is the gills. Fish display extreme hyperventilation, congregating in the direct flow of wavemakers (e.g., Wavemaker 530 GPH) or gulping at the surface.
- Velvet-like Dusting: When viewed at an angle under blue actinic lighting, the skin exhibits a fine, golden, rust-colored, or whitish dusting—similar to powdered sugar or velvet cloth. The spots are significantly smaller and more densely packed than Marine Ich.
- Severe Photophobia: Infected fish will actively hide in dark caves, avoiding the intense light of the display tank, an evolutionary response as dinospores are phototactic.
- Epidermal Sloughing: The skin begins to peel or slough off in advanced, necrotic stages.
Main Causes
Epizootiology
- Unquarantined Additions: The introduction of any wet item (fish, coral, macroalgae, or inverts) harboring encysted tomonts.
- Aerosolization: Rare but documented, dinospores can potentially cross-contaminate adjacent tanks via aerosolized water droplets from protein skimmers.
Treatments & Solutions
Emergency Chemotherapy
Immediate, aggressive intervention is mandatory; hours dictate survival.
- Freshwater Dip: An emergency 5-minute dip in temperature- and pH-matched RO/DI freshwater induces massive osmotic shock, bursting the trophonts and providing critical, immediate respiratory relief. This must be followed immediately by chemical treatment in a hospital tank.
- Copper (Cupric Sulfate): Sustained ionic or chelated copper maintained rigorously at therapeutic levels (2.0 - 2.5 ppm) for 30 days. Velvet is highly susceptible to copper.
- Chloroquine Phosphate (CP): The drug of choice for many modern aquarists against Velvet, dosed at 15 mg/L. It destroys the dinospores and disrupts the metabolic pathways of the trophonts.
Prevenzione & Biologia
Mandatory Biosecurity
- Strict Copper Quarantine: 30 days of therapeutic copper or Chloroquine for all new arrivals.
- Extended Fallow Period: The display tank must remain completely devoid of fish for 6 weeks (42 days) to guarantee the starvation of all dinospores.
Riferimenti Accademici e Scientifici
- [1]Merck Veterinary Manual: Parasitic Diseases of Fish
- [2]Dinoflagellates Amyloodinium and Ichthyodinium: morphology and molecular phylogeny of fish parasites
- [3]A highly specific PCR assay for detecting the fish ectoparasite Amyloodinium ocellatum
- [4]Study on amyloodiniosis outbreak in captive-bred percula clownfish and treatment response
- [5]Merck Veterinary Manual: Disorders and Diseases of Fish
Panoramica Clinica
Contagious
Mortality Rate
Avvertenza
Le informazioni presenti in questa scheda clinica hanno scopo puramente accademico e divulgativo. Consulta sempre un medico veterinario ittiopatologo per diagnosi certe e prima di somministrare farmaci.