Unpacking the Term: What is 'Drug Velvet'?
When aquarists ask, 'What is the drug velvet used for?', they are typically referring to the treatment of a parasitic condition known as Velvet Disease, also called Gold Dust Disease or Rust Disease. There is no single medication named 'Velvet'. Instead, the term describes a category of drugs used to combat the microscopic dinoflagellate parasites responsible for the infection: Piscinoodinium in freshwater fish and Amyloodinium in saltwater fish. These parasites give the fish a dusty, gold-to-brown 'velvety' appearance, hence the name. The disease is highly contagious and can be fatal if not treated promptly, primarily by causing respiratory failure as it attacks the gills.
The Parasite's Life Cycle
Understanding the parasite's life cycle is critical for effective treatment. It consists of three main stages:
- Tomont (Reproducing Stage): A mature parasite detaches from the fish, encysts, and falls to the aquarium floor. Inside this cyst, it divides into hundreds of free-swimming offspring. This encysted stage is resistant to most medications.
- Dinospore (Free-Swimming Stage): The cyst ruptures, releasing motile dinospores that swim through the water in search of a host. This is the stage where medications are most effective. These dinospores use photosynthesis for energy and must find a host within about 24-48 hours, or they will die.
- Trophont (Feeding Stage): Once a dinospore attaches to a fish, it becomes a trophont. It embeds into the skin and gills, feeding on the fish's cells and causing irritation, tissue damage, and the characteristic velvety sheen.
Identifying Velvet Disease: Symptoms and Diagnosis
Early detection significantly increases the chances of survival. The initial signs are often behavioral before the classic 'gold dust' appears.
Common Symptoms Include:
- Flashing: Fish rubbing or scraping their bodies against objects in the tank.
- Lethargy and Clamped Fins: Fish become less active and hold their fins close to their body.
- Rapid Breathing: A key sign that the parasites are attacking the gills, causing respiratory distress.
- Loss of Appetite: Infected fish often refuse to eat.
- Velvety Film: A fine, gold, rust, or grey-colored dust appears on the fish's skin. This can be hard to see, but a flashlight shone on the fish in a dark room can make it more apparent.
Formal diagnosis is best performed by an aquatic veterinarian who can take a skin or gill biopsy and identify the parasites under a microscope.
Medications and Pharmacological Treatments
Treatment must target the free-swimming dinospore stage of the parasite's life cycle. Because the cycle's length is temperature-dependent, treatment must be sustained for an extended period to eradicate all emerging parasites.
Copper Sulfate: This is a common and effective treatment, especially for marine velvet (Amyloodinium). Copper ions are toxic to the parasites. However, copper is also toxic to fish if dosed incorrectly and is lethal to invertebrates like snails and shrimp. Precise dosing and regular testing of copper levels are crucial for success and safety. Treatment duration typically requires an extended period to target the parasite throughout its lifecycle.
Chloroquine Phosphate: An antimalarial drug, chloroquine is highly effective against both marine ich and velvet. It is often considered gentler on fish than copper but is also toxic to invertebrates and should only be used in a quarantine tank. A typical treatment involves a specific concentration maintained for a period of time.
Hydrogen Peroxide: A newer approach involves using hydrogen peroxide baths. It works as a strong oxidizer that can break down the cell walls of the parasites, even in the attached trophont and encysted tomont stages. This method can eradicate the parasite much faster than copper but carries a risk of harming the fish if the concentration or duration is incorrect. It also destroys beneficial bacteria in the filter.
Supportive Treatments:
- Dimming Lights: Since the parasites are photosynthetic, keeping the aquarium dark for several days can weaken them and supplement chemical treatments.
- Raising Temperature: Increasing the water temperature to around 82°F (28°C) speeds up the parasite's life cycle, allowing the medication to kill the free-swimming stage more quickly. Ensure your fish species can tolerate the higher temperature.
- Aquarium Salt: For freshwater velvet, adding aquarium salt can help reduce osmotic stress on the fish and may inhibit parasite reproduction.
Treatment Comparison
| Treatment | Primary Target | Safety for Invertebrates | Key Considerations |
|---|---|---|---|
| Copper Sulfate | Free-swimming dinospores | No, highly toxic | Requires precise dosing and frequent water testing. Very effective but narrow safety margin. |
| Chloroquine Phosphate | External protozoan parasites | No, toxic | Considered gentler on fish than copper; must be used in a quarantine tank. Effective for a broad range of parasites. |
| Hydrogen Peroxide | All life stages, including trophonts | Not recommended | Fast-acting but experimental. High risk to fish if dosed incorrectly. Kills beneficial bacteria. |
| Salt & Darkness | Free-swimming dinospores (weakens them) | Yes (Salt may harm some plants) | Less aggressive method. Best for freshwater. Stresses the photosynthetic parasite. |
Conclusion and Prevention
In pharmacology, the 'drug velvet' is not one substance but a range of medications—primarily copper sulfate and chloroquine phosphate—used to combat a deadly parasitic fish disease. Successful treatment depends on correctly identifying the disease, acting quickly, and maintaining therapeutic levels of medication long enough to break the parasite's life cycle. The absolute best defense, however, is prevention. Quarantining all new fish for a minimum of four to six weeks in a separate tank is the most effective way to prevent Velvet and other diseases from ever entering your main display aquarium.
For more information on marine velvet disease, LiveAquaria offers a detailed guide to identification and treatment.
