Flukes in saltwater fish is fairly common and a parasite that fish keepers will inevitably come across during their time owning a saltwater, or even freshwater, aquarium.
For this reason, as aquarists, we need to be aware of where the flukes are most likely to attach to the fish and of the symptoms displayed by affected fish.
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What are flukes?
Flukes are a type of flatworm which fall under the group name Monogeneans. There are two main types that affect saltwater fish namely, Dactylogyrus and Gyrodactylus. Dactylogyrus affect the gills of fish and Gyrodactylus affect the skin.
Flukes are transparent members of the flatworm family which attach to fish with hooks. Their transparency and their microscopic size make identification by visual inspection almost impossible. This is why we have to rely on quarantining. This ensures that we are not inadvertently adding livestock to our display tanks with parasites such as flukes that could affect all the other fish and invertebrates. It also allows us to identify and swiftly deal with any other parasites or diseases that a new fish might have.
The life cycle of flukes
In a standard saltwater aquarium maintained between 77° and 78.8° Farenheit (or 25 and 26° Celsius), fluke eggs that were released into the aquarium’s water column, will mature and hatch. This usually happens within 4 – 6 days. The larvae which emerge finds a fish host and attaches itself at it’s preferred site on the fish using hooks which help keep it in place.
The fluke will remain hooked into the fish’s flesh for 17 – 19 days and feed. Once the fluke is mature, it will lay eggs into the water column and the cycle will begin again.
Fluke symptoms in marine fish
When a fish first becomes infected with flukes, there are no immediate indications. Unfortunately the following signs will confirm the existence of flukes:
Rapid breathing and swimming at the water surface. This is due to their inability to extract sufficient oxygen from the water as the flukes attach to their gills.
Lethargy. The fish may become lethargic, hiding amongst the rocks or in a corner of your tank
Lack of appetite. Fish may eat very little or nothing at all.
The development of clamped fins or fins that become frayed.
Cloudy eyes.
There may be loss of colour to the area of infection as the parasites take hold.
Your fish may be flashing against the rockwork to try and dislodge the flukes.
They may exhibit yawning or a have their mouth perpetually open. This is to enable the fish to process more oxygen exchange when the gills are affected.
The affected fish may appear to shake it’s head from side to side.
How to treat flukes
Due to the significant investment of treating flukes in aquaculture farming, we as reefers benefit from tried and tested methods.
The following three methods are the most commonly used when treating flukes, in order of effectiveness.
Method 1: Prazipro
The go to method is using a product called Hikari Prazipro.
Prazipro has been found to be very effective in the eradication of flukes in marine fish, and cannot be overdosed either. This is a gentle treatment, so gentle in fact that it can be used in a reef tank without any ill effect on corals and vertebrates, with the exception of wrasse. A wrasse may be temporarily removed into a separate tank until it is safe to return it to the main tank. (See this article on how I caught my wrasse.)
Prazipro does affect the oxygen levels in an aquarium and for this reason it is recommended that the water is aerated throughout the entire treatment. It may also reduce fish appetite.
Each treatment of Prazipro is between 5 and 7 days, with a large water change and a change of carbon following each. Multiple treatments may be required.
Once successfully treated, keep an eye on the affected fish for up to a month to ensure all flukes have been accounted for. You may still see your fish flashing against rockwork but this would be due to the affected areas healing.
Method 2: Hyposalinity
Hyposalinity refers to lowering the salinity to 1.011 SG. This has been proven to kill adults and juvenile flukes in 2 days. A further 3 days will kill the eggs.
Hyposalinity can be used in quarantine tanks, but not in reef tanks where corals rely on an SG of 1.025. Setting up a quarantine tank doesn’t have to be expensive. See how easy it is to set up a quarantine tank cheaply here.
It is also worth knowing that in some fish stockists it is common practice to keep their tanks in a state of hyposalinity.
Method 2: Freshwater Dips
This method is only effective on flukes that will come into contact with the freshwater, however if gills are affected, freshwater dips will not work.
How to prevent flukes
New fish:
As it is impossible to see if a fish is carrying flukes in the initial stage of the life cycle, the probability of a new fish introducing them into your aquarium is quite plausible.
For this reason, as well as being a good method of keeping any other illnesses or parasites out of your display tank, quarantining new additions is by the far best and highly recommended option. This includes clean up crew such as snails, hermit crabs, clams, feather worms etc.
A simple quarantine tank (QT) setup, which could be as basic as a large plastic container with a heater, could save a lot of problems and prevent loss of life in the future.
New live rock:
Always check your source. There may be a reason someone has shut down their tank and has live rock to sell.
New coral:
Use a coral dip to remove parasites from new coral you’re about to introduce into your tank. This will ensure that you are only introducing the coral and nothing else.
So there you have it!
If caught quickly enough you can save your saltwater fish from flukes. Please consider quarantining all new fish and invertebrates before adding to your display tank if you don’t already do so. You will never regret quarantining but you may regret losing your entire stock in your display tank if you don’t.
