Fish Not Eating? 8 Causes and What to Do

Why Fish Stop Eating

Few things worry an aquarist more than watching their fish refuse food. You sprinkle flakes or pellets into the tank, and instead of the usual feeding frenzy, your fish hide, spit food out, or simply ignore it altogether. If your fish are not eating in your aquarium, there is nearly always an identifiable cause — and in most cases, it is something you can fix.

Fish use feeding behaviour as a barometer of their overall well-being. A healthy fish in a comfortable environment will eat eagerly and consistently. When something is off — whether it is environmental, social, or physical — appetite is often the first thing to go. The key is to identify which of the eight common causes below applies to your situation, then take targeted action.

1. New Fish Stress (Just Added to the Tank)

Signs

• Fish hiding behind decorations, driftwood, or in corners
• Pale or washed-out colouration
• Darting or skittish movements when you approach
• Ignoring food entirely for the first 24-72 hours

Why It Happens

Moving from a shop bag to a new aquarium is enormously stressful. The water parameters, temperature, lighting, tank mates, and even the sounds are completely different. In Singapore, fish may have gone from a wholesaler in the Qian Hu or Clementi area through a retail shop and then to your HDB flat — that is multiple environmental changes in just days.

Solution

Give new fish time. Keep the lights dimmed for the first day, avoid tapping on the glass, and do not attempt to feed for at least 12-24 hours after introduction. When you do offer food, use small amounts. Most new fish will begin eating within 2-3 days. Providing hiding spots with plants or driftwood helps them feel secure enough to venture out and feed.

2. Wrong Food Type

Signs

• Fish approaches food, mouths it, then spits it out
• Food sinks uneaten to the substrate
• Some fish eat enthusiastically while others ignore the same food

Why It Happens

Not all fish eat the same food. Herbivores need algae wafers and blanched vegetables. Carnivores require protein-rich foods like bloodworms or brine shrimp. Bottom feeders may not even notice floating flakes. The food size also matters — a micro rasbora cannot eat a pellet designed for a large cichlid.

Solution

Research the dietary needs of each species in your tank. Offer a varied diet that includes options for all inhabitants. Sinking pellets for bottom dwellers, floating flakes or micro pellets for mid-to-top dwellers, and frozen or live foods as treats. A well-stocked approach ensures every fish gets what it needs.

3. Poor Water Quality

Signs

• Fish that were eating well suddenly stop
• Gasping at the surface
• Clamped fins or lethargy alongside appetite loss
• Cloudy or foul-smelling water

Why It Happens

Elevated ammonia, nitrite, or nitrate levels suppress appetite. In Singapore’s warm climate (28-32 degrees Celsius ambient), waste breaks down faster and dissolved oxygen levels are naturally lower, making water quality issues more acute. PUB tap water is treated with chloramine rather than simple chlorine, so insufficient dechlorination during water changes can also irritate fish and reduce appetite.

Solution

Test your water immediately using a liquid test kit. Perform a 30-50% water change with properly dechlorinated water if ammonia or nitrite registers above zero, or nitrate exceeds 40 ppm. Check your filter and maintenance schedule — in tropical Singapore, fortnightly water changes are the minimum for most setups. Ensure you are using a water conditioner that neutralises chloramine, not just chlorine.

4. Disease or Illness

Signs

• Appetite loss accompanied by visible symptoms: white spots (ich), cotton-like growths, bloating, red streaks on fins, or unusual swimming patterns
• Fish isolating from the group
• Rapid gill movement or laboured breathing
• Weight loss despite being offered food

Why It Happens

Sick fish divert energy from feeding to fighting infection. Internal parasites can cause fish to waste away even if they appear to eat. Bacterial, fungal, and parasitic infections are common, particularly after introducing new fish without quarantining.

Solution

Isolate sick fish in a hospital tank if possible. Identify the specific disease based on symptoms and treat accordingly. Maintain pristine water quality, as this alone can help fish recover from mild ailments. For persistent or serious issues, consult a knowledgeable aquarium shop — at Gensou, we regularly help customers diagnose and treat fish health problems.

5. Temperature Issues

Signs

• Lethargy and reduced movement overall
• Fish sitting on the bottom or hovering listlessly
• Appetite loss during particularly hot or cool periods

Why It Happens

Fish are ectothermic — their metabolism is directly governed by water temperature. In Singapore, the issue is almost always overheating rather than cold. During hot spells, tank water in an un-air-conditioned HDB flat can easily exceed 32 degrees Celsius, stressing tropical fish that prefer 24-28 degrees. Conversely, if your air conditioning runs very cold overnight, sudden temperature drops can also shock fish.

Solution

Use a thermometer to monitor water temperature. For tanks in warm rooms, improve surface agitation for evaporative cooling, use a clip-on fan, or invest in an aquarium chiller for sensitive species. Avoid placing tanks near windows with direct afternoon sun. If air conditioning causes temperature swings, use an aquarium heater set to 25-26 degrees to maintain stability.

6. Bullying and Intimidation by Tank Mates

Signs

• Specific fish not eating while others feed normally
• Chased away from food by dominant individuals
• Hiding constantly, only emerging when lights are off
• Torn fins or visible injuries

Why It Happens

Territorial or aggressive species can prevent subordinate fish from feeding. This is common with cichlids, certain barbs, and male bettas housed with timid species. In smaller tanks typical of HDB setups, there is less room for fish to establish separate territories, intensifying aggression.

Solution

Feed at multiple spots simultaneously to spread out competition. Use sinking and floating foods at the same time to separate feeding zones. Rearrange decorations to break up territories. If bullying is severe, consider rehoming the aggressor or the victim to a more suitable tank. Adding more hiding places with plants and hardscape can also help.

7. Overfeeding (They Are Simply Not Hungry)

Signs

• Fish pick at food lazily rather than eating with gusto
• Uneaten food accumulating on the substrate
• Slightly rounded bellies
• Algae bloom from excess nutrients in the water

Why It Happens

This is more common than most aquarists realise. Fish do not need as much food as many owners provide. A fish’s stomach is roughly the size of its eye. If you are feeding multiple times a day, or if multiple family members are each feeding the tank, your fish may simply not be hungry.

Solution

Reduce feeding to once or twice daily, offering only what fish can consume within two minutes. Skip feeding one day per week — this mimics natural conditions and is perfectly healthy. Coordinate with other household members to ensure the tank is not being double-fed. Remove uneaten food promptly.

8. Breeding Behaviour

Signs

• Male fish building bubble nests or displaying to females
• Female fish appearing plumper than usual
• Mouthbrooding species holding eggs in their mouths (and therefore unable to eat)
• Increased territorial behaviour

Why It Happens

During breeding, many fish prioritise reproduction over feeding. Male bettas guarding bubble nests will refuse food for days. Mouthbrooding cichlids do not eat for the entire brooding period, which can last two to three weeks. Female livebearers may eat less just before giving birth.

Solution

This is entirely natural and not cause for concern. Do not try to force-feed breeding fish. Continue offering small amounts of food so it is available when they are ready. Once breeding behaviour subsides, appetite will return to normal. Ensure water quality remains high, as the fish will be weakened after the breeding period.

How Long Can Fish Go Without Food?

Most healthy adult tropical fish can survive without food for considerably longer than many owners expect.

That said, regular feeding is important for long-term health, colour, and immunity. These figures are for emergencies and context, not a recommendation to fast your fish routinely.

Species-Specific Feeding Quirks

Some species are notoriously fussy eaters, and understanding their quirks can save you considerable worry.

Pea Puffers

Pea puffers are among the fussiest aquarium fish. Many individuals flatly refuse dry food — pellets, flakes, and freeze-dried options are often ignored completely. They typically require live or frozen foods such as bloodworms, snails, and brine shrimp. If your pea puffer is not eating prepared foods, this is normal behaviour, not a health issue. Offer live pest snails as a staple.

Scarlet Badis

Similar to pea puffers, scarlet badis are micro-predators that frequently refuse dry food entirely. Live baby brine shrimp, micro worms, and daphnia are usually necessary. Males are especially prone to hunger strikes and can be extremely picky. Patience and variety are essential.

Otocinclus

Otos are algae grazers that may appear not to eat because they feed on biofilm and algae you cannot easily see. They often refuse algae wafers initially. Ensure your tank has sufficient natural algae growth, or supplement with blanched courgette or cucumber.

Discus

Discus are sensitive to stress and water conditions, and appetite loss is often the first indicator of a problem. They are also hierarchical feeders — subordinate fish may not eat in the presence of dominant individuals. Feed a varied diet including high-quality pellets, frozen bloodworms, and beefheart preparations.

When It Is an Emergency

Not every instance of a fish not eating is urgent, but certain combinations of signs should prompt immediate action:

• Appetite loss plus gasping at the surface: Test water immediately. This suggests ammonia, nitrite poisoning, or dangerously low oxygen levels. Perform a large water change right away.
• Appetite loss plus visible disease symptoms: White spots, cotton-like growths, or red streaks indicate infection requiring treatment.
• Appetite loss plus bloating or pineconing scales: This may indicate dropsy, a serious and often fatal condition. Isolate the fish immediately.
• All fish in the tank refusing food simultaneously: This points to an environmental issue rather than an individual fish problem. Test water and check temperature urgently.
• Fry or juvenile fish not eating for more than 24 hours: Young fish have minimal energy reserves and can deteriorate rapidly.

If you are unsure whether the situation is serious, it is always better to test your water and err on the side of caution. A quick water test can rule out the most dangerous causes within minutes.

Frequently Asked Questions

My fish spits out food and then picks it up again. Is this normal?

Yes, this is completely normal for many species. Fish often “taste test” food by taking it in and spitting it out before consuming it properly. Some species, particularly cichlids, chew food by repeatedly spitting and re-catching it. This behaviour is only concerning if the fish consistently spits food out and never swallows it, which may indicate the food is too large or the wrong type.

Should I try live food if my fish refuses pellets and flakes?

Live food can be an excellent way to entice reluctant eaters. The movement of live brine shrimp, daphnia, or bloodworms triggers a natural hunting response that prepared foods cannot replicate. However, source live food carefully — poorly sourced live food can introduce parasites. Frozen alternatives are a safer option that still appeals to fussy eaters. Many aquarium shops in Singapore stock frozen bloodworms, brine shrimp, and daphnia.

How do I know if my bottom-feeding fish are eating enough?

Bottom feeders like corydoras, plecos, and loaches can be tricky to monitor because they often feed at night or when you are not watching. Check for a slightly rounded belly (not concave or sunken), consistent activity levels, and steady body condition over time. Drop sinking wafers or pellets in after lights-out when surface feeders are less active. A clean substrate each morning suggests your bottom feeders are doing their job.

Is it true that fasting fish one day a week is beneficial?

Many experienced aquarists practise a weekly fast day, and there is good evidence it benefits digestion, particularly for species prone to bloating such as goldfish and bettas. A rest day allows the digestive system to clear completely. It also mimics the natural feast-and-famine cycle fish experience in the wild. The exception is fry and juvenile fish, which should be fed multiple small meals daily for healthy growth.

If your fish are persistently refusing food and you have exhausted the troubleshooting steps above, it may be time for professional advice. At Gensou, our team has over 20 years of experience diagnosing fish health and behavioural issues. Visit us at 5 Everton Park or get in touch — we are always happy to help Singapore’s aquarists keep their fish healthy and thriving. If you suspect water quality is the underlying cause, our aquarium maintenance services can get your tank back on track.