All about Freshwater Velvet disease and how to treat it.
Author note: I now recommend using hydrogen peroxide to treat velvet.
Out of all the diseases that infect freshwater aquariums, Velvet is probably one of the most frustrating, deadly and difficult diseases to deal with. Velvet is particularly prevalent in wild bettas and blackwater fishes. If you have kept wild bettas for any period of time chances are you have encountered them. The disease can be easily diagnosed early on because of the typical gold like dust that covers the fish. Without treatment the death rate is quite high and in addition it is also extremely infectious, if one fish in your tank has it there's a high probability that all the fish in the tank (and other tanks) are infected.
Fig 1: typical appearance of velvet disease.
Life Cycle of Freshwater Velvet
Freshwater velvet is a type of Dinoflagellate in the genus Piscinoodinium, in most literature the exact species is Piscinoodinium pillulare but I suspect that in reality there are many different species and strains. Interestingly they are closely related to many photosynthetic plankton, and just like plankton they also have the ability to photosynthesis, though this is not their main way of acquiring energy and reproducing. Piscinoodinium sp. Have 3 life stages, this is important to understand as they are crucial to how to treat the disease.
Fig 2. Life stage of Piscinoodinium sp. Source (Kent & Sanders, 2020)
The first life stage is called the Tomont, Tomonts can be seen as a dormant version of the Piscinoodinium sp. and is almost resistant to most forms of medication and chemical treatment. With the exception of maybe formalin. This is because Tomonts are covered in a hard outer shell that protects it from being exposed to treatments. Tomonts are the reason why velvet often comes back after being eradicated. No one really knows how long the tomonts can stay dormant for but I believe it can potentially be weeks or months. To make matters worse they reside on the bottom of the tanks hiding in the substrates.
Before the Tomont hatch into Dinospores, they begin to divide themselves. Each Tomonts can divide itself hundreds up to 256 times before hatching into Dinospores (Kent & Sanders, 2020). Under optimal conditions 73.4-77 C Tomonts can become Dinospores in 10-14 days (Kent & Sanders, 2020).
The free swimming stage is called the Dinospores, Dinospores need to find a host within a few days or they will die. However Piscinoodinium Dinospores contain chlorophyll which allows them to survive without a host as long as there is available light (Lieke et al., 2020). This is why some people Cover the tank to treat the disease, but this doesn't work because they can simply survive off a host. The Dinospores is the ONLY stage that you can kill the parasites.
The third stage is called the Trophont, this is the stage where you can see the protozoan visually as the typical gold dust. Trophont are similar to Tomites in that they are covered in protective shells and are imobile, except they are actively feeding on their host through their rhizoid which they use to penetrate through the host epithelium (Lieke et al., 2020). Like Tomonts, Trophonts are very resistant against chemical treatment and there is very little you can do to remove them from the host except to wait till their life stage is over. At 77 C, trophont takes 6 days to fall off the host before they become Tomonts.
Why is Velvet so deadly?
Velvet disease is deadly because the Trophonts can spread and attach itself to the gills of the fish, this causes the fish to have difficulty breathing. This is often why you see infected fish stay near the surface gasping for air. When a fish dies from velvet, it is usually because they suffocate to death. Other issues the parasites can cause include necrosis of adjacent cells, irregular osmoregulation, and secondary infections from fungus and bacteria. When your fish is infected, they become lethargic, exhibit clamped fins and often stay near the surface. Weakened fish are unable to stay near the surface and eventually suffocate.
The other reason why Velvet disease is so deadly is because of the long infectious stage and the long dormant stage which can be 6 days and 12 days respectively. Under cool conditions this can be even longer. The period in which Velvet disease can be eradicated is extremely short from a few hours to a day, you have to kill the dinospores when it's at its free swimming stage and your window of opportunity is very limited. Because of this, fish with velvet will need to endure the infections for weeks before they get better.
Fig 2: scanning electron microscope image of Trophonts and its infections of the gills of Tambuca Hybrid fish (Martins, Moraes, Andrade, Schalch, & Moraes, 2001).
Best treatment for Velvet disease
There's many different ways that you can treat Velvet disease, but I'm going to show you the best and most practical ways to do it. Using chelated Copper Sulfate and increasing the temp to 84 degree F or above. In the infected tank, I raise the temperature up to 84 degrees F and dose Chelated Copper at 5ml per 5 gallon. And I keep it this way for 30 days.
Why do we increase the temperature to 84 degrees F or above
Increasing the temperature of the water quickens their life cycle, allowing the tomonts to become dinospores so that treatment can be used. Piscinoodinium sp. life cycle is HIGHLY influenced by the temperature of the water. In Fact, from my personal observation, very high temperatures can effectively eradicate the velvet disease alone. It seems prolonged exposure in very high temperatures, Piscinoodinium sp. Might actually die (though I have no evidence for this). Luckily for us, wild bettas and many blackwater fishes can tolerate temperature in the mid 80’s for quite a while, some species such as splendens even prefer that temperature.
Why do we use Chelated Copper Sulfate?
Copper base medication has been a very effective form of treatment against Velvet disease due to its toxicity to protozoans. However many copper medications are also deadly to fish and when it comes to wild bettas and many blackwater fishes, copper toxicity is increased significantly under acidic conditions. This is why Chelated Copper is the preferred choice because although it is less effective than nonchelated copper like cupramine, it is much less toxic to fish and you are less likely to overdose on copper if using chelated copper. The ideal concentration is roughly 1.5 - 2.0 ppm copper but I personally do my copper at about 5ml per 5 gallons using CopperSafe. Chelated copper also has the benefit of being active in the water for 14 to 30 days. This is extremely important! Because only the free-swimming dinospore stage of the parasite is killed, the Trophont can stay on the host for 6 days, and the Tomont which can be dormant in the substrate for 14 days.
The best product I use for the treatment of velvet disease is coppersafe by mardel
Dinospores needs to be exposed to Copper for a period of time.
Many people think that copper immediately kill dinospores, this is not true. Dinospores can be exceptionally resilient and infect fishes before they are killed by copper exposure. This is why in heavily stocked tanks, velvet disease is notoriously difficult to get rid of. The dinospores reinfect another fish before they are exposed to copper long enough to die. To combat this, you need to make sure your tank is not heavily stock, the larger the body of water the more time the copper and heat can get to work on eradicating the disease.
Why do we need to treat it for 30 days?
Because of the dormancy stages of Velvet, to truly eradicate the disease you would need to treat it for 30 days. Fishes can look healthy and normal but still be carrying the parasites on them, likewise tomonts can be hidden in the substrate somewhere and since they are unaffected by copper they can release dinospores when you think the infection is over. This is why many people have velvet and often have it come back and reinfect again after weeks of eradicating the disease.
UVC filters can be a very effective form of quickly killing the dinospores. However it needs to be set up correctly and many people do not have the correct knowledge of how to use UVC. The dinospores are killed by the UVC because it causes DNA damage, for this to occur it needs to be exposed to UVC at a certain wavelength with minimum light intensity over a specific amount of time, this is referred to as “Dwell time”. Unfortunately many popular UV filters do not offer the correct light intensity and even wavelength, they are really only good for eradicating algae. From my experience you need to have at least 36 W high quality UVC bulb pushing wavelength at the ~250nm with a rated dwell time for your tank for it to be effective, you can measure this by finding the GPM (gallon per minute) a filter is capable of moving water through it, slowing water flow through a UV filter makes it more effective.
Treatment that is not effective against velvet.
Heat and salt
I hear this alot, even from experienced fish keepers. This is because it has historically been the treatment for a lot of diseases when information isn't widely available for people to research. Heat and salt is extremely effective for Ich because the salt affects the osmosis pressure of the Ich parasites, but it has very little effect on Piscinoodinium sp.. Piscinoodinium sp. Is quite salt tolerant and many of its related cousins infect marine fish. However, that doesn't mean salt is completely useless, salt has a therapeutic effect of reducing the chances of secondary infection which can often kill the fish before velvet does. Success from using Heat and Salt actually comes from the Heat alone, because temperature above 84 degrees disrupt the reproductive abilities of the velvet disease as well as reducing its dormancy. Trophonts stay on the body of the fish for 2-3 days instead of 6 and tomonts might have difficulty dividing and reproducing, dinospores might even have less time to find a host before it dies.
Indian Almond Leaves
Some people think that Indian Almond Leaves have magical healing properties. But whatever it is that it does, it has no effect on velvet. What IAL really does is reduce the PH of the water (as long as your water is already soft with very little buffer to begin with!) which reduces the toxicity of ammonia on fish. The reduction in ammonia toxicity can help with sick fish but does nothing to fight against the parasites.
submersible low wattage UVC
As explained before, low quality UV filters might not have the correct wavelength and might only be outputting at the ~280nm this is ineffective for Velvet as the wavelength is too long to reach the DNA of the parasites. Furthermore, many in tanks and submersible UV filters move water through it too fast to be effective, there simply isn't enough dwell time for the UV light to affect the dinospores.
Condition that causes Velvet outbreak.
Drop in temperature
Velvet disease usually occurs through the introduction of fish that carry the parasites. However infected fish often show no symptoms for many weeks until something triggers the disease to break out. This trigger is often caused by the decrease in the immune system of the fish. In Wild bettas, one of the most common triggers appears to be a rapid decrease in temperature. Wild bettas live in tropical habitats where the daytime and night time water temperatures do not differ significantly. However in the home environment where water bodies are significantly smaller, a change of 15 degrees over a period of an hour really negatively affects the fish. Water temperature that quickly drops below 73 degrees can cause the fish to all of a sudden have an outbreak. This is why it is important that you have a heater in your tank at all times to keep the temperature stable. Wild bettas and blackwater fishes can be happy in the low 70s as long as they stay consistently at the low 70s.
Overstock or stressed fish from aggression
Another trigger that causes a velvet outbreak is when a fish is under a stressed condition from tank mates. Bullying is very common in wild bettas kept together and aggressive fish can often bully and beat up the subordinate fish. Fish under stress can have low immune systems causing them to be susceptible to velvet infections or if they have been carrying the disease an outbreak. It's important that if you are keeping wild bettas or blackwater fishes in groups you carefully remove aggressive domineering fish so that other fish in the tank aren't stressed. Making sure that you have adequate space and that the tank isn't overstocked is one of the best ways to resolve this issue.
Some things to know
Velvet is an extremely frustrating disease to deal with. Don't be surprised that your fish still dies even if you have done everything correctly. The death rate for velvet is very high particularly in very old or very young fish. Furthermore chemical treatment with heat and copper can be stressful for some species leading to secondary infections and death. The best way to treat velvet is to make sure you don't have an outbreak in the first place by having good fish practices.
Kent, M. L., & Sanders, J. L. (2020). Important parasites of zebrafish in research facilities. The zebrafish in biomedical research (pp. 479-494) Elsevier.
Lieke, T., Meinelt, T., Hoseinifar, S. H., Pan, B., Straus, D. L., & Steinberg, C. E. (2020). Sustainable aquaculture requires environmental‐friendly treatment strategies for fish diseases. Reviews in Aquaculture, 12(2), 943-965.
Martins, M. L., Moraes, J., Andrade, P. M., Schalch, S., & Moraes, F. R. d. (2001). Piscinoodinium pillulare (schäperclaus, 1954) lom, 1981 (dinoflagellida) infection in cultivated freshwater fish from the northeast region of são paulo state, brazil: Parasitological and pathological aspects. Brazilian Journal of Biology, 61, 639-644.