Clamped fins

Fins held tight against the body, reduced activity or hiding — a general stress signal. Compare your fish with the reference photo above and cross-check your logged parameters in Aquarium Tracker before medicating.

SymptomClamped fins

CausesAmmonia or nitrite present — most urgent / Temperature outside species range

TreatmentTest ammonia, nitrite, nitrate and temperature immediately / Perform a partial water change if ammonia or nitrite is detectable

PreventionQuarantine new fish; zero ammonia & nitrite

What causes clamped fins?

Ammonia or nitrite present — most urgent
Temperature outside species range
pH far from species preference or sudden pH swings
Overstocking, bullying or recent aggressive tank mates
Recent water change shock, medication or new decor

What to check before medicating

What to measure	Typical target	What an off reading points to
Ammonia (NH₃/NH₄⁺)	0 ppm	Anything above zero means the biological filter cannot keep up. Toxic to fish long before it is high enough to feed algae.
Nitrite (NO₂⁻)	0 ppm	A reading above zero points to an immature or disrupted filter — common after a media change, medication, or a large clean.
Nitrate (NO₃⁻)	5–20 ppm planted · under 10 ppm reef	Climbing nitrate signals more waste going in than water changes and plants export. Near zero in a planted tank starves plants and favours algae.
Temperature	within your species range, steady	Warmer water holds less oxygen and speeds both metabolism and pathogen growth. Sudden swings stress fish more than a steady figure at either end.
pH	stable, within your species range	Stability matters more than the number. A drifting pH usually means depleted KH or a CO₂ swing rather than a pH problem in itself.
Stocking level and mix	suits volume, footprint and temperament	Crowding raises waste and stress together, which is why disease often follows a new addition rather than a parameter change.
Recent changes	note anything from the last 2–3 weeks	New livestock, plants, media, lighting or dosing are the usual trigger. The cause often precedes the symptom by a fortnight.

Take these readings first. A large share of what looks like disease is a water quality problem, and medicating a tank whose ammonia is climbing treats the symptom while the cause keeps working.

Treatment steps

Test ammonia, nitrite, nitrate and temperature immediately
Perform a partial water change if ammonia or nitrite is detectable
Review tank mates for aggression and provide hiding places
Reduce feeding until water quality is stable
Avoid adding medication until water parameters are corrected

Prevention

Test ammonia, nitrite and nitrate on a schedule rather than only when something looks wrong
Keep parameters stable — sudden swings after a large water change cause more problems than the readings they correct
Avoid overstocking; crowding raises waste and stress at the same time
Feed only what is eaten in a few minutes, and remove the rest

Frequently asked questions

Is clamped fins contagious to my other fish?

Treat the whole tank as exposed until you know otherwise. Even non-infectious causes usually reflect a tank-wide condition, so the other fish are living in whatever triggered it.

How quickly do I need to act?

Act within a day or two. Most conditions are far easier to reverse early, and a fish that has stopped eating has usually been unwell for longer than it has looked unwell.

Should I treat in the display tank or a hospital tank?

A separate hospital tank is preferable where the fish is well enough to move: doses are easier to control, and many medications harm invertebrates, plants or the biological filter. Treat in the display only when the whole tank is affected or moving the fish would add more stress than the treatment removes.