Goldfish sitting on the bottom of the tank

A goldfish that has stopped swimming and settled on the bottom is doing the one thing a healthy goldfish rarely does during the day. Goldfish are grazers, built to cruise and pick at things for hours, so stillness is a signal. At night, or in a quiet dark room, it is usually sleep. In the daytime, with fins pulled in and gills working hard, it is most often a reaction to the water, the temperature, or something living on the gills — fast or laboured breathing works through that half of the picture. Sorting out which takes a few minutes of watching and a test kit.

Resting or unwell?

A resting goldfish holds its fins loosely, breathes slowly, hovers just above the substrate or leans lightly on it, and comes alive within a minute of the lights going on or food hitting the water. An unwell one clamps its fins, breathes visibly faster than its tankmates, ignores food or takes it half-heartedly, returns to the bottom as soon as it can, and often loses colour.

How goldfish actually rest

Worth knowing properly, because half the traffic to this page is about a perfectly healthy sleeping fish.

Goldfish have no eyelids, so they cannot close their eyes and there is no outward sign that looks like sleep to us. What they do instead is enter a reduced state: they stop swimming actively, hover low or settle on the substrate, hold their fins relaxed rather than folded, breathe slowly, and respond more slowly to movement in the room.

They usually do it at night, and they do it in the same place — a corner, a spot behind an ornament, low in the water in the darkest part of the tank. A fish that returns to the same spot every evening is not hiding; it has a bedroom.

And they go pale. This one alarms people regularly and is usually normal: the pigment in a goldfish’s skin cells can pull in at night, so a fish that is deep orange in the afternoon can look washed out when you turn the light on at seven in the morning, and returns to full colour within minutes. Slow fading in a permanently bright, bare tank is a different process, a fade over weeks as the pigment cells themselves change. The lighting page covers giving the tank a proper day and night, which matters more to the fish than the brightness does.

The distinguishing test is how fast it comes back. A resting fish rouses within a minute of the lights coming on or food hitting the water, and then behaves normally. A fish that takes a long time to respond, or that rouses, eats and immediately returns to the bottom, is not resting.

Look three times

A very useful discipline on this page, and it costs nothing.

One glance at a tank tells you very little, because whether a goldfish is on the bottom depends enormously on the hour. Check at three separated times — first thing in the morning before the lights have been on long, in the middle of the day, and in the evening — and write down what you see each time.

The patterns this reveals:

• On the bottom in the morning, active by midday, fine in the evening. Usually an overnight oxygen dip, particularly in a planted or warm tank. Aeration is the fix and gasping at the surface is the related page.
• Fine in the morning, subdued by evening. Often a room that warms through the day, or a tank in afternoon sun.
• Down at all three checks. A real problem, and the water test matters most.
• Down only when you are in the room. The fish is reacting to you, which points at a recent fright, a new tank, or simply a fish that has not settled.

Telling the causes apart

If every fish in the tank is subdued, the water is the suspect. Ammonia and nitrite make fish go still and breathe hard, and the whole tank suffers together, usually with a history: a new tank, extra fish, a filter cleaned in tap water, a missed water change. Cold does the same thing more gently. A pond goldfish sitting quietly on the bottom in January is fine, but a fancy in an unheated room after a cold night is not, and a sudden swing of a few degrees can knock a fish flat for a day.

If the fish sits low but comes up to gasp now and then, or the tank is warm, crowded and has a still surface, think about oxygen; our page on goldfish gasping at the surface goes through that in detail.

Flicking against decor, a milky sheen of extra slime, heavy or uneven gill movement and restlessness between spells on the bottom point to gill or skin flukes, which cannot be seen with the naked eye.

If only one fish is affected, watch for bullying at feeding time — chasing and bullying covers what to look for, including the version where the others are ignoring rather than pursuing it, which points at illness instead — and look at its body shape. A round fancy that struggles to lift off but can swim when it tries probably has the sinking version of the buoyancy problems that make other goldfish float.

What to do first

Test ammonia, nitrite, nitrate and pH, and read the thermometer. If ammonia or nitrite is present, do a 30–50% water change (at least half if ammonia reads 2 mg/L or more, unless the pH is below about 6, when smaller daily changes are safer) with conditioned, temperature-matched water, feed lightly, and repeat daily until both read zero. If the temperature is out of range or has swung, correct it gradually, no faster than about 1 °C an hour and more slowly for a sick fish, and shield the tank if it sits by a window or radiator; the temperature guide covers what stable means in practice. If the surface is still, add an air stone or angle the filter outlet to break it. Then watch feeding time for chasing.

Supportive care while you investigate

None of this treats anything. All of it lowers the demand on a fish that is already short of margin, and it is what to do in the days between noticing and knowing.

• Soften the flow. A weak fish holding station against a current spends energy it does not have. Spread the filter outflow or angle it away from the floor of the tank — the filtration guide covers how.
• Dim the light, or shade part of the tank, so the fish has somewhere less exposed.
• Give it somewhere to rest out of the main flow: a smooth ornament, a plant, anything that breaks the line of sight without sharp edges.
• Keep the room quiet. No tapping, no faces at the glass, no rearranging.
• Feed lightly or not at all. A fish that is not moving is not digesting much, and uneaten food worsens the water it is already reacting to.
• Hold the temperature steady rather than trying to improve it. A swing is a second problem on top of the first.
• And keep testing. Daily, while it is unwell.

Winter, and pond fish on the bottom

Seasonal and important, because the instinct to help does real harm here.

As pond water falls below about 10 C, a goldfish’s metabolism slows until it is barely digesting. The fish settle in the deepest, most thermally stable water and stay there, moving little, for weeks or months. This is correct behaviour, not illness, and the whole of a pond through the year is built around it.

What that means in practice:

• Stop feeding. Below roughly 8 to 10 C the fish cannot process food, and food that sits in the gut undigested causes real harm. The seasonal feeding page covers the taper and the spring restart.
• Do not disturb them. No netting, no moving, no prodding to check they are alive.
• Do not bring them indoors to warm up. A fish taken from 4 C water into a 20 C room is subjected to a severe shock, and the same again in reverse in spring. Pond goldfish overwinter outdoors perfectly well.
• Keep a patch of surface open if the pond freezes, so gas exchange continues. Melt a hole with a pan of hot water set on the ice; never break it with a hammer, which can harm the fish below.
• Spring is a risky time as well as winter. Fish come through with their immune systems slowed while the filter is still cold and the water is warming, which is when problems often appear.

An older fish rests more

Worth ruling in rather than out, once everything else is clear.

An elderly goldfish genuinely does spend more time still. It cruises rather than darts, takes longer to reach food, and rests more often and for longer — and none of that is a problem if the fish still eats well, holds itself level, breathes calmly and has clean water around it. The lifespan page covers what ageing looks like and, importantly, what it does not cause.

The caution is that “it is just old” requires no action, which makes it the easiest explanation to reach for and the easiest to be wrong about. A water test costs nothing and rules out the thing that is actually most likely. Age is what is left after the other explanations have been eliminated, not a substitute for eliminating them.

When it is something else

A fish that stays down and breathes hard after a large water change, with clean tests and a good temperature, needs a parasite ruled out; flukes in particular can only be confirmed by a vet examining a skin or gill scrape under a microscope. A fish that has not eaten for several days, or shows bloating, red streaks or sores, has moved beyond watching and waiting.

Preventing it

Nearly every case comes back to water, temperature or space. A cycled filter, a tank large enough for its fish, weekly water changes, good surface movement and a stable temperature away from drafts and sun remove most of the reasons a goldfish ends up on the bottom. Quarantining new fish keeps flukes out.

Summer is the season to plan for, which is the opposite of what people expect. Warm water holds less dissolved oxygen, and a goldfish’s demand for it rises at the same time, so the two curves move against each other. A crowded or poorly aerated tank that is comfortable at 20 °C can leave fish resting on the bottom at 27 °C with nothing else changed and the usual water tests normal. If a room reaches the high twenties in July, the answer is more surface agitation before the weather arrives rather than after: an air stone, the filter outlet raised to break the surface, the lid propped open. Sitting on the bottom in hot weather is a fish conserving effort, and it is one of the few versions of this that can turn into laboured breathing within a day.

Give the bottom a reason to be comfortable. A fish that rests on bare glass does so on a hard, reflective, slightly abrasive surface, and one already unwell will sit there long enough to mark itself. A smooth, shallow substrate and one low, soft-edged place to rest against mean that the resting a healthy goldfish legitimately does costs it nothing.

And a fish that rests at night, in the dark, with its fins relaxed and its gills moving slowly, is simply doing what goldfish do. Knowing your own fish’s normal resting habit is what makes the abnormal version obvious, and there is no substitute for having watched it when nothing was wrong.