One of the first things I get told when looking at an aquarium is:
“Ash, my fish aren’t eating.”
And usually the next question is:
“What medication should I put in?”
My answer is nearly always the same:
“Let’s work out why first.”
A fish not eating doesn’t automatically mean it’s sick. Sometimes there’s a very simple reason. Other times, it’s the first sign that something is wrong with the aquarium.
Here’s what I’d check.
1. Check your water first
This is always one of the first things I’d look at.
Your fish live in the water 24/7. If something is wrong with the water, they’re going to feel it.
Ammonia and nitrite are two big ones. In a healthy established aquarium, both should be zero.
And don’t assume the water is fine because it looks crystal clear. I’ve seen plenty of tanks that looked perfect but had water parameters that were causing problems.
If your fish suddenly stop eating, test the water before reaching for medication.
2. Have you recently moved the fish?
If you’ve just bought new fish and put them into your aquarium, don’t panic if they don’t eat straight away.
They’re stressed. They’ve been caught, bagged, transported and then introduced into a completely new environment.
Give them some time to settle.
One of the worst things you can do is keep adding food because you’re worried they aren’t eating. The food doesn’t disappear. It just sits there and becomes waste.
3. Something has changed in the aquarium
Think back. Did you recently:
- Change a lot of the water?
- Move decorations?
- Change the filter?
- Add new fish?
- Add medication?
- Completely clean the aquarium?
- Move the tank?
Fish don’t always appreciate us redecorating their house every weekend.
If they were eating normally and suddenly stopped after you’ve made a change, that’s worth looking at.
4. The temperature could be wrong
Different fish have different temperature requirements.
If your tropical aquarium is sitting too cold, your fish can become sluggish and lose their appetite.
Check the thermometer. And don’t just assume the heater is working because the light on the heater is on. I’ve seen heaters fail before. A cheap thermometer can save you a lot of guessing.
5. You’re feeding the wrong food
This one sounds obvious, but it happens all the time.
Not every fish eats the same thing.
Some fish feed from the surface. Others feed from the middle or bottom of the aquarium. Some need a mainly plant-based diet, while others need more protein.
If you’ve got a fish that doesn’t seem interested in its food, make sure you’re actually giving it something suitable.
6. You might be feeding too much
This is probably one of the most common problems I see.
People think: “My fish are hungry, I’ll give them a bit more.” Then five minutes later there is food all over the bottom of the tank.
Fish don’t need a huge amount of food. Give them what they can reasonably eat in a few minutes and remove anything that’s left over.
Overfeeding doesn’t just waste food. It creates more waste, which can affect your water quality. And now you’ve potentially gone from a feeding problem to a water-quality problem.
7. Is another fish bullying it?
Watch your aquarium at feeding time. Don’t just throw the food in and walk away.
Is one fish chasing another? Is one fish getting all the food? Are smaller or more timid fish hiding until feeding time is over?
Sometimes a fish isn’t refusing food at all. It’s simply not getting a chance to eat. This is particularly common in African Cichlid aquariums and other tanks where fish can be territorial.
8. Look for signs that your fish is sick
If your fish hasn’t eaten and something else doesn’t look right, start paying closer attention.
Look for things like:
- Rapid breathing
- Hiding constantly
- White spots
- Clamped fins
- Swollen belly
- Loss of colour
- Scratching against rocks or decorations
- Swimming strangely
One symptom doesn’t necessarily tell you what’s wrong. But if your fish has stopped eating and is behaving differently, don’t ignore it.
9. Your fish might simply not be hungry
This is one people don’t like hearing.
Sometimes your fish just isn’t hungry.
If the fish is swimming normally, looks healthy, is behaving normally and your water parameters are good, missing a meal isn’t necessarily a disaster.
Don’t immediately change everything because your fish skipped one feeding. Watch what’s happening. Your fish’s behaviour will tell you a lot.
10. You’re looking at the wrong fish
This sounds strange, but hear me out.
If you’ve got several fish in the aquarium, you might think they’re all eating because the food disappears.
But is every fish actually eating? Sometimes one fish is getting pushed away or hiding while the others are eating everything.
Take a few minutes and watch the tank properly. You might find the problem isn’t that your fish won’t eat. It’s that your fish can’t get to the food.
So, what should you do?
If one of your fish suddenly stops eating, don’t panic. I’d start with the basics:
Check the water. Check the temperature. Watch the fish. Watch the other fish. Think about what has changed.
And don’t start adding medications just because a fish has skipped a meal. Work out the cause first.
That’s something I see quite often with aquarium owners. They try to fix the fish when the actual problem is the aquarium.
Fix the environment and quite often the fish starts eating again.
When should you be concerned?
If your fish hasn’t eaten for several days and you notice other symptoms, that’s when I’d take it seriously.
Especially if you see rapid breathing, sitting on the bottom, gasping at the surface, loss of colour, unusual swimming or multiple fish suddenly refusing food.
That’s no longer just a feeding issue. Something else could be going on.
My advice from years of maintaining aquariums
Don’t judge your aquarium just by how clear the water looks.
And don’t judge your fish just by whether it eats one meal.
Look at the whole picture. Water quality, temperature, filtration, stocking, feeding and fish behaviour all work together.
A healthy aquarium isn’t about constantly adding products and trying to fix things. It’s about getting the basics right and keeping them stable.
If you’re in Melbourne and you’ve got fish that aren’t eating, or you’re not sure what’s going on with your aquarium, Aquatics by Ash can help with water testing, troubleshooting and regular aquarium maintenance.
Sometimes catching a problem early is the difference between fixing an aquarium and trying to save one.