Velvet, gold dust disease, rust disease, Oodiniasis, and Oodinium are all names for one pesky foe. The protozoa that cause velvet were once classified as Oodinium, hence the other names for velvet, but has since been reclassified to Piscinoodinium because they’re partially photosynthetic. But a rose by any other name, right?
There are several species of protozoa that fall under the name “velvet”; P. amyloodinium, P. crepidoodinium, P. pillulare are a few, but they can all be treated (more or less) the same way. Both fresh and saltwater fish can contract this protozoan parasite. It acts in a way that’s similar to ich, where the parasite forms cysts on the fish’s skin, scales, and gills. This similarity is likely because they both come from protozoa. But that’s where the similarities between the two stop.
Velvet isn’t a particularly unsightly disease, so it’s not uncommon for someone to purchase a fish because of the beautiful gold speckling that fish has. It’s only when this gold speckling begins to spread, or they observe the fish scratching that questions start to bubble up. If you’re among this lot of folks, know that you’re not alone (*raises hand too.*)
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So, let’s get down to the brass tax, how do we beat this rusty foe?
Table of contents
Gold Dust Disease FAQ
Can humans get velvet from fish?
Humans can’t get velvet disease from fish since it’s not zoonotic (meaning humans can catch the disease from other species.) You can, however, have it live on your skin while your skin is wet and transfer this disease from tank to tank.
How long can a fish live with velvet?
It depends on how severe the case is and how warm the water is. At higher temperatures, velvet produces faster, and the infestation intensifies. It also depends on how stressed the sick fish is. But, in general, it’s best to deal with the illness as soon as you can to prevent fatalities.
Can fish die from velvet?
Yes, velvet can be lethal to fish. A particularly nasty infestation could wipe out your fish in a few days. Though typically velvet is only contracted when the fish’s immune system is weak to begin with, so the additional stress may be what kills them more than the parasite itself.
Velvet isn’t particularly hard to diagnose, as far as illnesses go. How many symptoms and which symptoms a fish has depended heavily on the species and the severity of the outbreak but, in general, here’s what you might see:
- Gold or brownish “dusting” on the fish
- Itching and scratching against surfaces
- Bloody streaks on the body or fins
- Excessive mucus
- Opacity in the eyes
- Clamped fins
- Loss of appetite
- Ulcers on the skin
- Detachment of the skin or loss of scales
- Exophthalmia (bulging or mislocation of eyes)
We already talked about how velvet is a protozoan parasite that’s caused by several different species. But where does it come from, and how do some fish get it while others don’t?
- Stress: Stress plays a significant role in immune system responses. When fish (or people, or any living thing, really) are stressed, their immune system is suppressed. Stress presents a perfect opportunity for all sorts of things to creep into their body.
- Undeveloped immune system: this is the case when fry come down with velvet.
- Newly Introduced fish: a recently introduced fish is, not only stressed, but likely stresses out established inhabitants as well. This intro is a prime opportunity to add a pathogen.
- Newly introduced plants: pathogens can come in on any surface that was in an infected tank, including plants.
Velvet Life Cycle
Ich and velvet have incredibly similar life cycles. There are a few key differences in their life cycle; however, namely that velvet needs light to survive, whereas ich couldn’t care less.
Trophont (Velvet You See On Fish)
Trophonts attach to the fish and gnaw on the skin and tissue of your poor fish and photosynthesizing. As your fish’s skin becomes irritated, their immune system encysts the velvet in a dome-like bubble.
This “bubble” is what you see when your fish has velvet – but it isn’t velvet itself, just a reaction. The bubble limits the damage these parasites can do to the surrounding tissue, but it also makes the trophonts harder to kill since medication can’t penetrate this bubble. This stage of the life cycle lasts six days at tropical temperatures, but higher temperatures will speed it up, and lower temperatures will slow it down.
Once mature, the trophonts will burst from this bubble and will be called…
Tomont or Palmella (“Reproductive” Velvet)
Trophonts leave their protective fish bubble to fall to the floor of your aquarium – or any spot they land. This stage is where the “adults” (tomonts) will divide into hundreds of baby velvets, more or less. (Although scientists would likely frown and call them dinospores.)
This stage is incredibly temperature-dependent. Tomont division happens fastest between 79 – 80F (26C), and this stage can complete in three days at this range. At lower temperatures, it can take up to six days, and the time to finish treatment is, as a result, more time-consuming as well.
Once replication is complete, the tomonts will burst and release hundreds of dinospores into the water.
This stage is incredibly temperature-dependent. Tomont division happens fastest between 79 – 80F (26C), and this stage can complete in three days at this range. At lower temperatures it can take up to six days, and the time to finish treatment is, as a result, more time-consuming as well.
Once replication is complete, the tomonts will burst and release hundreds of dinospores into the water.
Domites (Free-Swimming Velvet)
Domites, once released, will swim around until they latch onto a fish. But they’ll rest on plants, decor, in the gravel – basically, anywhere they see fit. At this stage, velvet is easily transferred from tank to tank. However, while it’s most contagious, it’s also easiest to kill.
Domites can only survive for 48 hours without a host. Once the domites attach to fish, they become trophonts, and the cycle starts over again.
Depending on the water temperature, the whole cycle can take a few days to weeks. There is no hard and fast answer for how quickly they’ll go through their life cycle.
There are a few methods you can use to treat velvet, but before we get to those, I suggest you follow these steps first for any plan of attack:
Step 1: Water Change
Unless you literally just changed the water – like today – I would advise you to change it. There are a few reasons why but, for one, your fish will likely sit in the water their in for a few days if you add meds to their water. Two, it helps get rid of some of the free-swimming and “adult” velvet that are left in your tank, hopefully reducing the number in your tank out the gate.
Step 2: Add Air
Start pumping some air into the tank now since your water is currently at a lower temperature, and it will hold oxygen better.
If you can saturate the tank as much as possible before raising the temp, your fish will have an easier time breathing once it gets hotter. Trying to do this the other way around is much more difficult (and less effective.)
Step 3: Increase Temperature
Temperature increases help speed up the life cycle of velvet so you can kill them faster. The max, if you can, would be 89F (31C), but if you can get your temp up to at least 86F (30C), that should be high enough. If you have cold-water fish like goldfish, or if your fish are less heat resistant you can take your temp up as high as you (and they!) feel comfortable going.
Slowly bring your temperature up by one or two degrees every few hours – you don’t want to shock them. The same is true for bringing the temp back down (but more on that in a minute.)
Step 4: Turn Out The Lights
Turn out your aquarium lights and, if you can, cover it with a towel or a blanket to make sure no light from the room or outside can get it. Velvet is photosynthetic meaning that, like plants, it needs light to survive. Without light, you have a better chance of killing this foe once and for all (well, maybe that’s too far.)
Once that much is done, you can…
Treat Velvet With Medication
There are some medications on the market that treat velvet with the use of copper and quinine. Cupramine and PraziPro are good choices. Of course, these medications cause issues for a host of fish including invertebrates, rays, pufferfish, loaches, and catfish, to name a few, so it might not be a safe route for some tanks. It is, however, highly effective at ridding fish of velvet if you find your fish aren’t sensitive to those chemicals.
Acridine, acriflavine, and the like are safer to use but are more effective on freshwater velvet than brackish or saltwater.
Treat Velvet With Heat, Salt, & Darkness
When medication is not an option (which is common with sensitive fish), you can use salt in combination with heat and darkness to treat velvet – though you need to proceed slowly with this method.
If you want to attempt this method, bring the temp as high as your fish are comfortable going.
Providing your fish can go to warmer temperatures, try bringing the temperature up to 82 – 86F (27 – 30C.)
It’s advised to add one to three teaspoons of aquarium salt per gallon of water in your aquarium. You can mix this solution is a one-gallon jug and slowly add the brine solution over a few hours. Just be sure to monitor for stress in the fish over this time. If you’re feeling crafty, you can hook the jug up to an irrigation dripper (or make your own) where it will slowly drip into the tank, no extra work needed on your part.
It’s worth noting that this method is, obviously, not suitable for tanks with snails or most invertebrate species.
Most fish are exposed to velvet at some point in their life and, like ich, once exposed, they tend to develop and immunity to future reinfection. While it’s not entirely avoidable, you can prevent massive outbreaks from forming in your tank by
1. Quarantine new fish and plants:
Quarantining won’t avoid the need to cure velvet with some newly acquired fish, but it will significantly reduce the risk of infecting fish you already have as well as make it easier to cure. A adequately set up quarantine tank should be bare (no gravel, no plants, etc.) And while it may seem above and beyond to quarantine new plants, if you purchased your plants from a tank with fish in it, this step is entirely necessary. Just because you don’t see velvet on the fish in the tank, doesn’t mean it’s not there.
2. Avoid using wet equipment on more than one tank:
Even if your tanks are healthy, avoiding using wet equipment on more than one tank is an essential step in preventing cross-contamination. This includes nets, siphons, pumps, heater, plants – basically anything. Wait a few hours for it to dry out before you put it in a new tank.
3. Reduce live food use:
Unless you culture your own live food, in which case, disregard. But if you frequently buy feeder fish, blackworms, bloodworms – or any other live food – it’s best avoided until you can culture your own. This prevents a ton of the risks associated with live foods. Avoiding live food may be nearly impossible with obligate piscivores that are difficult (or impossible) to get on a frozen food diet – but these instances are rare in home aquariums.
Further Reading & Resources
Science Direct – Protection against velvet disease in goldfish recovered from ichthyophthiriasis
USM.edu – Studies on Amyloodinium ocellatum(Dinoflagellata) in Mississippi Sound: Natural and