What do fish eat? Choosing the right food for your aquarium fish

Not all fish food is the same, and not all fish eat the same thing. Some fish hunt worms and insects. Some graze algae off rocks all day. Most eat a bit of everything. A fish can eat well every day and still go short if its food is wrong for it: a meat-eating pleco given only algae wafers, or a plant eater given only meaty flakes.

Each species card on this site has a Diet line that tells you what kind of eater the fish is. This guide explains the food types and how to choose. For how often and how much to feed, see how often and how much to feed.

How to check it

Read the Diet line on each species card. It shows one of these:
- Carnivore (meaty foods): eats insects, worms, shrimp and other small animals. Examples: bettas, zebra plecos, most killifish, puffers.
- Herbivore (greens and algae): eats mostly plants and algae. Examples: bristlenose plecos, mollies, many Lake Malawi mbuna. "Grazers" such as otocinclus and hillstream loaches scrape algae and the thin film of tiny life on rocks and glass.
- Omnivore (eats most foods): eats both. Most community fish, such as tetras, guppies, corydoras and goldfish, are omnivores.
- Wood: some plecos, such as Panaque, rasp on driftwood as part of their diet.
Check where each fish feeds. Species cards also say whether a fish swims near the top, mid-water or on the bottom. Surface fish take floating food; bottom fish need food that sinks.
Look at mouth size. Food has to fit the mouth. A neon tetra can't eat a large pellet, and a big cichlid may ignore tiny flakes.
Watch a feeding. Who gets the food, and who misses out? Does food sink past the fish, or float away to the filter?
Read the label on your food tub for the main ingredients and the date. Fish meal, shrimp or insects first suits carnivores; spirulina, algae or vegetables first suits herbivores.

When it's a problem

Normal: fish eat eagerly, keep good colour and have gently rounded bellies.
Early signs of the wrong food: a fish that ignores what you offer, stays thin while others look fine, or slowly loses colour.
Serious: plant eaters chewing every plant to stubs, poor growth or bent spines in young fish, or a bloated fish (see bloated fish and Malawi bloat, which is linked to the wrong diet in plant-eating cichlids).
Urgent: a fish that has stopped eating altogether. That's usually illness or bad water, not food; test the water and see fish dying.

What to do right now

List your fish and their Diet lines. Note any carnivores, herbivores and wood eaters.
Check that every group has a food that suits it, and that it reaches them: floating food for surface fish, sinking food for bottom fish.
Check the dates on your food. Throw out anything that smells stale, has gone clumpy or damp, or was opened many months ago.
Don't add lots of new foods at once. Try one new food at a time, in small amounts, and remove what isn't eaten so it doesn't foul the water (see overfeeding).

What to do next

Types of fish food

Flakes: thin, soft and good for small and mid-water fish. They float, then sink slowly. They lose quality fastest once opened.
Pellets and granules: come in floating and sinking types and many sizes. Floating pellets suit surface fish such as bettas. Sinking pellets reach corydoras, loaches and plecos. Choose a size that fits the smallest mouth in the tank.
Wafers: flat discs that sink and soften slowly, made for bottom fish and plecos. Algae wafers suit grazers; there are also meaty wafers for carnivorous bottom fish.
Gel food: a powder you mix with hot water that sets into a jelly. It holds together in water, so slow bottom feeders can graze it for hours. Good for plecos and loaches.
Frozen food: bloodworm, brine shrimp, mysis, daphnia and more. Rich in protein and very popular with fussy eaters and carnivores. Thaw a small cube in a cup of tank water first.
Live food: baby brine shrimp, daphnia, microworms, blackworms. Excellent for fry and for getting fish into breeding condition. Home-cultured live food is safest; live food from ponds can bring in diseases and parasites.
Vegetables: blanched courgette (zucchini), cucumber, peas with the skin removed, and spinach. Weigh pieces down with a fork or veggie clip. Take them out within a day before they rot.
Wood for plecos: wood-eating plecos such as Panaque rasp driftwood, and many other plecos graze it too. Research by a UC Irvine scientist found these fish can't digest much of the wood itself and lost weight on wood alone, so wood belongs in the tank as part of the diet, not as the whole diet. See what do plecos eat.

Matching food to the fish

Diet line	Main foods	Extras
Carnivore	High-protein pellets or granules sized to the mouth	Frozen or live bloodworm, brine shrimp, mysis
Herbivore and grazer	Spirulina or algae-based flakes, pellets or wafers	Blanched vegetables, gel food, algae on rocks
Omnivore	A good flake or pellet	Frozen foods and vegetables now and then
Wood	Vegetables and algae-based foods	Driftwood always in the tank

Some fish don't fit their group's usual menu. The zebra pleco looks like an "algae eater", but Seriously Fish describes it as preferring meaty food, and it rarely takes algae or vegetables. Always check the species, not just the family.

Variety

Use one good staple food plus two or three others through the week, such as a frozen food and a vegetable or gel food. No single food is perfect, and variety covers the gaps. It also keeps fussy fish interested.

Storing food

Buy small tubs. UF/IFAS advises buying fish food often and never keeping it for more than about three months. Vitamins, especially vitamin C, break down over time, and the oils in fish meal go rancid.
Keep dry food cool and dry, in its sealed tub, away from the tank lights and heater. Don't keep dry food in the fridge, where it can pick up moisture.
Keep frozen food frozen. If it thaws and refreezes, throw it out.
Write the opening date on the lid.

Products that help

A quality staple flake or pellet sized for your fish.
Sinking pellets or wafers for bottom fish.
Algae or spirulina-based food for herbivores and grazers.
Frozen foods for carnivores and variety.
Gel food mix: easy to pack with vegetables or protein.
Veggie clip or stainless steel fork to hold vegetables down.
Driftwood for plecos.
Feeding tube or long tweezers to put food right in front of bottom fish.
Airtight containers and a marker pen for dating opened food.

How to prevent problems

Check the Diet line before you buy a fish, and make sure you can feed it.
Keep fish with similar diets together where you can. A tank of plant-eating mbuna is easier to feed well without meaty fish in with them.
Feed at the level each fish lives: floating food for top fish, sinking food for bottom fish, often at lights-out for nocturnal plecos and loaches.
Rotate foods through the week.
Replace dry food every few months.
Remove leftovers to protect your water quality.

Why it matters

A fish's gut is built for its natural diet. Plant eaters have long guts made to slowly break down plant matter; rich meaty food can upset them. Meat eaters need protein and can't get enough from plant foods. Fish also need vitamins they can't make for themselves, and dry food loses them as it ages. Over weeks or months, the wrong or stale food shows up as poor colour, slow growth, weak fry and fish that get sick more easily.

When to get help

If a fish stays thin after a few weeks on the right food, it may have internal parasites; see internal worms and camallanus worms.
If a new fish won't eat anything you offer, ask the store or breeder what it was eating.
If several fish show bent spines, faded colour or poor growth, talk to a fish vet or an experienced breeder of that species.

In the game

Multiple Tank Syndrome doesn't have a feeding card, but each fish's diet still matters. Fish with a Grazer or Wood diet count as algae eaters: they can go into a tank hit by "Algae takeover", which takes no other new fish until an algae eater goes in, and they clean the algae up. Wood-eating plecos (along with goldfish and oscars) are plant eaters: when one goes into a tank, it tears up every plant there, and any plant planted with it later is eaten straight away. In a real tank, wood-eating plecos are hard on plants too, so stick to tough plants tied to wood or rock.

Sources

UF/IFAS Extension: Fish Nutrition (FA096) (food types, pellet size, storage and vitamin loss).
Seriously Fish. Hypancistrus zebra (a meat-eating pleco).
Seriously Fish. Sewellia lineolata (a grazer that eats algae and biofilm).
German DP, UC Irvine. Wood-eating catfishes research notes (Panaque can't digest much wood and lose weight on wood alone).