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Corydoras are normally active, enthusiastic foragers — when they stop eating or appear disinterested in food, it is almost always a sign that something is wrong. Because corydoras feed at the bottom and are often overlooked at feeding time, appetite loss can go unnoticed longer than in mid-water fish. This guide walks through the most common causes in order of likelihood so you can identify and address the issue quickly.
Most Common Reasons Corydoras Stop Eating
1. Food Not Reaching Them
This is the most common reason corydoras appear not to be eating — and it is not actually a health problem. In a community tank, mid-water fish often consume all available food before it reaches the bottom. Corydoras that appear lethargic or uninterested may simply be underfed rather than ill. Switch to sinking pellets or wafers, feed in the evening when mid-water fish are less active, and observe directly whether the corydoras are consuming food. See our Corydoras Feeding Guide.
2. Poor Water Quality
Elevated ammonia or nitrite is one of the most reliable causes of appetite loss in corydoras. Even moderate levels suppress feeding behavior before causing visible physical symptoms. Test water immediately if corydoras stop eating unexpectedly. If ammonia or nitrite is detectable, perform a 25–50% water change immediately and identify the cause of the spike. See our Best Water Test Kits guide.
3. New Tank Stress
Corydoras that have just been introduced to a new tank will often refuse food for 24–72 hours while they acclimate. This is normal and not a sign of illness. Keep lighting subdued, avoid disturbing the tank, and give newly added fish time to settle before becoming concerned. Ensure the tank is fully cycled and the school is large enough — both significantly affect how quickly new fish settle.
4. School Too Small
Corydoras kept in groups below 6 of the same species experience chronic stress that suppresses normal behavior, including feeding. A school that has dropped below 6 due to losses will often become lethargic and stop foraging actively. Adding more fish to restore the group to 6 or more often resolves the behavior within a few days.
5. Temperature Problems
Corydoras become lethargic and stop eating when water temperature drops outside their preferred range. Check the heater and verify temperature with a reliable thermometer. A failed heater, particularly overnight in cooler months, is a common cause of sudden appetite loss. Temperature instability — even within the acceptable range — can also suppress feeding. See our Best Aquarium Heaters guide.
6. Barbel Damage
Corydoras with severely eroded or infected barbels have difficulty locating and consuming food from the substrate. If corydoras appear to be searching for food but not eating, inspect the barbels closely. Healthy barbels should be intact and pointed. Eroded, stubby, or inflamed barbels indicate a substrate or water quality problem that needs to be addressed. See our Corydoras Barbel Erosion guide.
7. Disease
Loss of appetite is a common early symptom of several corydoras diseases:
- Ich: Fish may stop eating before white spots are visible. Look for flashing behavior and clamped fins as early indicators.
- Red blotch disease: Bacterial infection causing red patches on the body, often accompanied by lethargy and appetite loss.
- Fin rot: Bacterial infection of the fins, usually secondary to poor water quality. Fish may become lethargic and stop eating.
- Internal parasites: Corydoras with internal parasites may eat but remain thin, or may stop eating entirely. Sunken belly despite apparent feeding attempts is a warning sign.
Inspect fish carefully for visible symptoms if appetite loss is accompanied by behavioral changes. See our Corydoras Diseases guide.
8. Incorrect Substrate
Corydoras on sharp or coarse gravel may reduce foraging activity to avoid barbel pain. If corydoras are spending less time at the substrate than usual and appear reluctant to forage, substrate may be a contributing factor. Switching to soft sand or very fine smooth gravel resolves this over time as barbels heal.
Immediate Steps If Corydoras Stop Eating
- Verify food is actually reaching them — switch to sinking pellets and feed in the evening
- Test water immediately — ammonia, nitrite, nitrate, and temperature
- Inspect barbels — check for erosion, infection, or damage
- Count the school — ensure there are at least 6 of the same species
- Check temperature — verify heater is functioning and temperature is stable
- Inspect fish for visible symptoms — spots, red patches, fin damage, sunken belly
- Perform a water change if any parameters are elevated
- Try a high-value food — frozen bloodworms often trigger feeding in reluctant corydoras