Whitespot disease (ich)

What you can and cannot establish yourself

Cause

A ciliate protozoan that burrows under the outer skin layer to feed — Ichthyophthirius multifiliis

Spread between fish

Spreads rapidly through a system

Urgency

Act today

Affects

fish

Confidence

high confidence

Signs

• Discrete white specks on the body and fins, roughly 0.5–1 mm across, raised rather than flat
• Spots have defined edges and sit individually rather than merging into a film
• Flashing — the fish scrapes its flank against decor, substrate or the glass
• Clamped fins and reduced activity
• Rapid gill movement where the gills are involved
• In a heavy infection, spots increase over several days rather than appearing all at once

Do this first: the environmental response

Water quality is the cause, the contributing factor or the deciding variable in the great majority of aquarium health problems. These steps come before any treatment decision, and for several conditions they are the entire treatment.

1. Test ammonia and nitrite first. An outbreak commonly follows a water-quality problem, and treating the parasite while the water is still damaging the fish addresses half the problem.
2. Increase aeration. Gill involvement reduces oxygen uptake, and most treatments reduce dissolved oxygen further.
3. Warming the water shortens the parasite's life cycle and brings the vulnerable free-swimming stage forward, which is why it is a standard part of the response. It is only appropriate within the range the species actually tolerates, and it must be done gradually and with extra aeration — warm water holds less oxygen at exactly the moment the fish can least afford it.
4. Do not raise the temperature for species that are not warm-water animals. For a goldfish or a white cloud mountain minnow the temperature that would accelerate the parasite is itself a stressor.
5. Continue the response for several days beyond the disappearance of visible spots, because the disappearance means the feeding stage has dropped off, not that the infection has ended.

What else it could be

Every entry names the observation that separates it from this record. Work through these before deciding what you are treating — the most expensive mistake in fish health is confident treatment of the wrong thing.

What makes it more likely

Each entry states the mechanism, not just the association — an association without a mechanism is not something you can act on.

• Recent addition of fish without quarantine. The parasite arrives with a carrier fish, often one showing no visible spots because its own infection is light and established.
• Chilling or a sudden temperature drop. Cold stress suppresses the fish's immune response while the parasite remains viable, which is why outbreaks classically follow a heater failure or an unheated shipment.
• Crowding. Free-swimming infective stages must find a host within roughly a day. The more fish per litre, the higher the proportion that succeed.
• Chronic poor water quality. Sustained ammonia or nitrite exposure damages gill and skin epithelium and depresses immune function, so an exposure that a healthy fish would clear becomes an outbreak.

Treatment categories

AquariumHQ names classes of response and never doses. Product concentrations differ between markets and formulations, several actives are temperature- and pH-dependent, and the invertebrate and plant tolerances that decide whether the rest of the tank survives are not printed on the label. Where a category puts a chemical in the water, what it can damage is stated with it.

Isolation and quarantine

• Isolating the visibly affected fish does not protect the others. By the time spots are visible the free-swimming stages are already distributed through the tank, so the whole system is the unit that has to be dealt with.
• Treat the display tank, not a hospital tank, unless there is a specific reason not to — moving one fish out leaves the parasite in the tank you moved it away from.
• Do not move equipment, nets or plants from an affected tank to a clean one without drying or disinfecting them.

When a vet is the right call

• Fish continue to die after several days of appropriate response
• Spots that do not respond to treatment, which suggests the identification was wrong
• Gill involvement with laboured breathing and no visible spots
• A valuable or long-lived animal where a confirmed identification is worth the consultation

Prevention

• Quarantine every new fish, including fish from a trusted source, for long enough to cover the parasite's life cycle at your quarantine temperature.
• Match temperature carefully when acclimatising, and avoid chilling during transport.
• Keep separate nets and equipment for quarantine and display tanks, or dry them fully between uses.
• Maintain stable water quality — the outbreaks that become serious are almost always the ones where the fish were already compromised.

What AquariumHQ does not know

Published rather than hidden. A health page that lists no limitations has not had its limitations looked for.

• AquariumHQ does not hold species-level susceptibility data. Reports that particular aquarium species are more prone to whitespot are widespread and, as far as we can establish, not supported by controlled comparison — differences in husbandry, origin and transport stress are confounded with species in almost every account.
• The exact life-cycle duration at each aquarium temperature varies between reported strains, so AquariumHQ gives the relationship rather than a table of days.

Evidence

Each claim is shown with what kind of support stands behind it and how strongly we hold it. Those are separate axes: a measurement held tentatively and an editorial position held firmly are different things.

Related

• fish gasping at surface
• quarantine
• temperature
• dissolved oxygen