A fish that's hiding and not eating in an otherwise established tank is usually showing the earliest sign of stress or illness, often before any visible symptom appears. Test your water first — a hidden water quality issue is the most common cause — then watch closely for developing symptoms over the next few days.
Why is my fish hiding and not eating?
Fish often show behavioral changes before any physical symptom shows up. Hiding and refusing food are the two most common, and they usually trace back to one of a handful of causes.
Water quality
This is the most common cause by far. Ammonia or nitrite that's crept above zero, a nitrate level that's been building between water changes, or a temperature swing from a failing heater all stress fish well before they cause visible damage. A test kit reading takes five minutes and rules this in or out immediately.
Recent changes in the tank
A new tankmate, rearranged decor, a big water change, or a move to a new tank can all cause temporary stress on their own. This kind of hiding usually settles within a few days as the fish adjusts.
Bullying from tankmates
A fish that's being chased or nipped will retreat to cover and stop coming out at feeding time, even when the water is fine. Watch the tank for a few minutes around feeding — if one fish is consistently pushing another away, it's a stocking and aggression problem, not an illness.
Early illness
Less commonly, it's the early stage of an illness that hasn't developed external symptoms like white spots or fin damage yet. Loss of appetite is often the first thing that changes, a day or two before anything is visible.
Normal behavior for the species
Some fish hide by nature. Plecos, many catfish, and loaches are shy or nocturnal and spend most of the day under cover, feeding after the lights go off. If the fish has always behaved this way and looks healthy, it may not be a problem at all.
New fish hiding and not eating
A newly added fish hiding for the first few days is normal. Transport, a new tank, new water, and new tankmates are all stressful at once. Most new fish start eating within two to three days, and some timid species take up to a week. Keep the lights a little dimmer, avoid chasing the fish around with a net, and offer small amounts of food daily rather than heavy feedings it won't eat.
Why are my fish not eating but not hiding?
A fish that's out and active but ignoring food often has a feeding issue rather than a health one. The food may be too big for its mouth, the wrong type (a bottom feeder won't chase flakes at the surface), or something it doesn't recognize as food yet. Cool water also slows a fish's metabolism, so check that your heater is holding the right temperature. If a fish is active but also looks bloated or is producing stringy waste, overfeeding or constipation is a common cause.
How long can a fish go without eating?
A healthy adult tropical fish can go several days to a week without food without lasting harm, so a short hunger strike isn't an emergency on its own. What matters more is why it's not eating. Don't keep adding food to tempt it — uneaten food breaks down into ammonia and makes any water problem worse. Remove anything not eaten within a few minutes.
Should I be worried right away?
A day of reduced appetite after a stressful event, like adding new fish or doing a big water change, usually isn't a concern on its own. It's worth acting on when hiding and appetite loss persist for several days, or when other symptoms start appearing alongside it: clamped fins, faded color, rapid breathing, or gasping at the surface.
What to do
- Test your water first — ammonia, nitrite, nitrate, pH, and temperature. Fix anything out of range with a partial water change.
- Watch closely for any developing symptoms (spots, discoloration, clamped fins) over the next few days.
- Watch feeding time to rule out bullying from tankmates.
- Reduce other stressors: check tankmate compatibility, avoid unnecessary decor changes, and keep feeding consistent.
- Try a different food (sinking pellets, frozen or live food) if the fish seems interested but isn't taking what you offer.
- Consider a quarantine tank if you suspect illness, so you can observe closely without risking the rest of the tank.
Hiding vs. other problems
| What you're seeing | Likely cause | Guide |
|---|---|---|
| Hiding and not eating, no other symptoms yet | Stress or early illness | This guide |
| Hiding specifically from other fish | Aggression or stocking issue | Aggression guide |
| Gasping at the surface | Low oxygen or acute water quality | Gasping guide |
| Floating sideways or struggling to stay upright | Swim bladder problem | Swim bladder guide |
Not sure what's going on? Run the 2-minute fish diagnosis to narrow it down, or see the full stress and early illness guide for what to check next.