White spot is arguably the most common disease that tropical fish are subject to, and is believed to be responsible for causing more fatalities than any other disease. Most – if not all – aquarists will encounter white spot (also known as Ich) at least once or twice during the course of their career/hobby.
What is it?
White spot is a single-celled, ciliate protozoan. In regular English, this means it’s a single celled parasite organism, which propels itself through the water through use of cilia, or filament-like hairs. Mature adult cells are 0.5 – 1.0 mm in size, and are usually clearly visible to the naked eye.
White spot is a parasite. It lives under the top layer of scales and skin on your fish, eating skin cells and causing minute cellular ruptures. The white spots which result from these ruptures are the basis for the parasite’s name, and are what will eventually kill the host (the fish).
How does it get into my tank?
White spot is usually introduced to a tank along with new, infected fish or plants. It can also break out seemingly without warning in an undisturbed tank.
When this happens, it means that the organism has been present for some time, but has been dormant (hibernating), and that some new stimulus – stress, or a change in water temperature – has caused it to awaken and become active.
The original cell of the organism will attach itself to a host (the weakest, oldest, or sickest fish in the tank), usually in the gill plates or under the scales.
After approximately one week of parasitism, the now-mature organism (mature Ich cells are called trophozoites) detaches from the fish and settles on a new surface: usually, a plant or ornament.
It will then form a capsule around itself (called a cyst) and will remain dormant – at least, outwardly – for about a week. During this period of time, the cell within the capsule is furiously dividing: by the time that those seven days are up, that one cell has become approximately 1,000 new single-celled organisms.
These “daughter cells” will then break loose and swim freely about the tank, attaching themselves to new fish – and beginning the cycle all over again.
White spot is highly contagious and progresses very rapidly. 100% mortality is to be expected unless something is done about it.
What can I do about it?
Prevention is obviously the best cure:
1. Make sure you only ever buy healthy fish from a reputable, clean breeder
2. Inspect the tank from which your fish originate: does it look to be in clean condition? Are the plants healthy and flourishing? Is the gravel clean of sediment and dust? Is the water warm and well-conditioned?
3. Check the fish, too – not just the ones you’re buying, but all the fish in the tank. Watch out for ones that are ‘hiding’ (under rocks and behind ornaments) since this is a classic symptom of an infected fish. Make sure none are displaying those tell-tale white spots
4. Thoroughly clean any gravel or ornaments you purchase before placing them in the tank, to make sure any cysts are dislodged
5. Quarantine new plants and fish for one week before adding them to your tank
6. Never overstock your tank, since it will stress the fish (which is a major contributor to outbreaks of white spot, as well as dictating in part the severity of the outbreak)
7. Check your fish regularly for white spots. The earlier you detect it, the less impact the disease will have on your tank.
What if it’s too late for prevention?
If you’ve already got an outbreak in your own tank, relax – it may be a serious illness, but at least it’s easy to cure!
The most common, and user-friendly, method of curing condition is through the use of aquarium salts.
Parasites are less tolerant of salt than fish, so adding extra salt kills off all the Ich organisms with no adverse effects to the fish themselves. Make sure you follow the instructions on the package (aquarium salts should always come with clear instructions), and make sure before using it that you don’t have any salt-intolerant fish in the tank like Neons, Cardinals, Glow-Lights, or scale-less Catfish, which are easily burned by salt.
A second alternative is to use a chemical called malachite green. This is an effective way of treating Ich, but unfortunately the chemical is toxic to humans (as well as most plants and snails, so make sure you remove these before commencing treatment!). Always use gloves when administering this chemical – and, because it’s teratogenic (meaning it harms fetuses), pregnant women should stay well away from it.
All you have to do with malachite green is remove the carbon from the filter, and add the appropriate amount (according to the instructions) to the water of the tank. It usually takes about 4-5 days to kill all the Ich cells – a good rule of thumb is to continue use of it until a couple of days after the last white spot has vanished from the fish. 10 days is typical for use of malachite green: just remember to put the carbon back in the filter to remove any lingering traces of the treatment, and give it one or two more days before putting the snails and plants back in.
UV light is also an effective means of treatment: you can purchase inner-tank filters from the pet store with small UV lights inside them. The light kills the parasites in the capsule stage, before they attach to the host.
The transfer method is time-consuming but effective: you’ll need to move all the fish, daily, into a new tank with clean, warm, conditioned water. It takes about 7 daily transfers (so, a week) for all the parasites to fall behind. The only downside is that the fish (and, often, the aquarist!) get stressed by the process, leaving them more susceptible to other diseases. Fish already affected by white spot will sometimes die during the transfer process because their bodies can’t handle the additional stress.
For a complete compendium of information on all the problems that tropical fish are subject to, take a look at Katy’s Tropical Fish – A Complete Guide.You’ll learn how to keep your fish happy, healthy, and beautiful, how to keep your aquarium to professional standards, how to troubleshoot health problems as soon as they occur, and learn valuable insider tips and tricks for keeping your aquarium looking spectacular.