Why is my fish not eating? Causes and what to do today
Fish won't eat? A new fish skipping food for 1–3 days is normal; an established fish refusing two meals needs a water test today. The checks, in order.
By Xavier Jodoin
In short
A new fish that skips food for one to three days is normal; an established fish that refuses two meals in a row is a water test today. Check the temperature first, then ammonia, nitrite and nitrate, and change 30–50 % of the water if anything reads wrong. If the refusal comes with bloating, white spots, gasping or ragged fins, that other symptom names the problem, and its guide has the treatment.
The fish that ignores the food
Feeding time is the one moment every fish in the tank shows up, which is why a fish that stays behind is the first sign most keepers notice. It hangs back, takes a pellet and spits it out, or ignores the food as it drifts past and sinks. Sometimes it is one fish, sometimes the whole tank.
A lost appetite is not a disease. It is the most general symptom a fish has, the way a fever is for us: something is wrong, and appetite is the first thing a fish gives up. The work is finding what. Three questions narrow it down faster than any list of causes: how long has it been, is it one fish or several, and is anything else different about it.
How long, and which fish
A new fish, for the first one to three days. Normal. It has been netted, bagged, driven home and dropped into water that tastes different, and it may never have seen your brand of food. Keep the lights low, offer a small pinch once a day, and remove what it ignores. Most new fish eat by the third day; wild-caught fish and shy species can take a week.
An established fish that skips one meal. Watch it. Fish are not machines, and a single missed feed after a big meal, a water change or a spell of chasing is not a problem. Offer again tomorrow.
An established fish that refuses two meals or more. Test the water today. This is the point where waiting stops being patience and starts being lost time, because the usual causes get worse the longer they run.
Several fish at once. It is almost certainly the water. Diseases start in one fish and spread over days; a whole tank going off its food on the same morning points at something every fish shares.
- 1
A new fish, first one to three days
Normal. Lights low, a small pinch once a day, remove what it ignores
- 2
An established fish skips one meal
Watch it. Offer again tomorrow
- 3
An established fish refuses two meals or more
Test today: temperature, ammonia, nitrite, nitrate
- 4
Several fish stop eating at once
Almost always the water. Test and change 30–50 % if anything reads wrong
- 5
Refusal plus bloating, spots, gasping or ragged fins
The other symptom names the problem. Go to its guide
The three tests to run first
1. Temperature. Fish are cold-blooded, and their appetite follows the thermometer. A tropical fish below about 22 °C slows down and stops eating; a betta at 20 °C lies on the bottom. A heater that failed overnight or a cold snap in an unheated room is the single most common cause, and the cheapest to fix. Goldfish are the exception: they eat less as water cools and stop almost entirely below 10 °C, which in a pond in winter is normal.
2. Ammonia and nitrite. Both burn the gills, and a fish that cannot breathe comfortably does not eat. Any reading above zero in a cycled tank is the answer: change 30–50 % of the water now, with a dechlorinator and matched temperature, and test again tomorrow. The ammonia spike guide has the full routine.
3. Nitrate. Nitrate that has crept past 40 ppm over weeks does not kill quickly; it wears fish down, and appetite goes first. The fix is a regular water change schedule, starting with two 25 % changes this week.
If all three read well, check pH against your last few tests. A sudden drop after months of stable readings, usually because KH ran out, stresses every fish in the tank; the parameters guide explains what the numbers should be.
In the app — log the readings and the verdict says which ones are off and by how much, with the water change already sized to your tank. The trend chart shows whether nitrate has been climbing for weeks, which is the usual story behind a fish that has slowly gone off its food.
When it comes with another symptom
A lost appetite rarely travels alone for long. Whatever arrives with it is the more useful clue.
Bloating. A round belly after a big feed and a fish that floats or sinks is usually constipation, and the swim bladder guide covers the fast-and-pea fix. A swollen body with scales standing out like a pinecone is dropsy, which is much more serious and needs treatment today.
White spots like grains of salt. Ich. Fish stop eating as the parasite reaches the gills. A fine gold or rust dusting you can only see under a torch is velvet, which kills faster.
Gasping at the surface. Oxygen or gills. Check ammonia and nitrite first, then whether the water is warm and still with no surface movement; the gasping guide has the ten-minute routine.
Ragged, shrinking fins. Fin rot, almost always in water that has been dirty or cold for a while. Grey-white patches on the mouth that spread in days are columnaris.
Long white stringy faeces and a hollow belly. An internal parasite, or an internal bacterial infection. The fish is losing weight while its tankmates eat; that needs a checkup and a medicated food, not a better diet.
Hiding, clamped fins, torn fins on the others. Bullying. A fish that is chased away from every meal looks like a fish that is not eating. Watch a whole feed from start to finish before you assume it is ill.
Species notes
Bettas spit food out when it is too big, too hard or unfamiliar, and they refuse flakes outright once they sink. A cold betta and an overfed betta are the two classic non-eaters; the betta guide covers both.
Goldfish eat everything, so a goldfish that refuses food is a stronger signal than most. Check the water first, then look for floating after meals, which points at swim bladder trouble from dry floating food.
Bottom feeders such as corydoras and plecos often look like they are not eating when the food never reaches them. Drop a sinking wafer after the lights go out and see if it is gone by morning.
Cichlids guarding eggs or fry eat very little for a week or two. So do many fish during a spawn. If the pair is healthy and the rest of the tank is fine, leave them to it.
Getting a fish eating again
Fix the cause first. No food tempts a fish that is sitting in ammonia or cold water, and once the water is right most fish start eating again within a day or two without any help.
For a fish that is recovering but still picky, feed tiny amounts of something it cannot resist: frozen bloodworm, daphnia or brine shrimp, thawed in a little tank water. Drop them near it, not across the tank. Feed with the lights dimmed if it is shy. Remove anything uneaten after five minutes, because rotting food is the last thing a struggling tank needs.
In the app — a checkup with a photo, your readings and Not eating ticked gives Finley the whole picture, and he says what the likely cause is and what to do first. The follow-up the next day asks whether it is eating again, so a fish that is not improving does not slip through a busy week.
Common questions
How long can a fish go without eating?
A healthy adult tropical fish can go a week, often two, without food, which is why skipping feeds over a holiday is safer than an automatic feeder that overdoses the tank. A sick fish that is not eating is a different matter: it is burning reserves it needs to recover, so find the cause within a day or two rather than waiting for hunger to fix it.
Why is my new fish not eating?
Stress and unfamiliar food. A fish that has been caught, bagged and moved into different water usually refuses food for one to three days, and it may not recognise your brand of pellet. Keep the lights low, offer a little once a day and remove what it ignores. If it still refuses after a week, or shows any other symptom, test the water and run a checkup.
Why is my fish spitting out its food?
Usually the food is too big, too hard or unfamiliar, and the fish takes it, tests it and rejects it. Try smaller pellets or soak them in tank water first. A fish that spits out food it used to eat, and looks thinner, may have a mouth injury or the start of an infection, so watch it closely for a day or two.
Should I stop feeding a fish that is not eating?
Stop dropping in food it will not eat, because uneaten food rots and makes the water worse. Offer a small amount once a day and take out what is left after five minutes. Keep feeding its tankmates normally, and put the effort into the water tests and the cause instead.