What Do Fish Eat? The Short Answer
What do fish eat? The honest answer is almost everything, as long as it fits in the mouth. A neon tetra picks mosquito larvae off the surface. A koi roots through pond mud for worms. A pleco rasps algae from glass. A tuna chases squid across open ocean. Fish are the most varied group of vertebrates on Earth, and their diets match that variety.
That range is also why so many pet fish are fed badly. A flake tub says “tropical fish” on the label, but a betta, a goldfish and a pleco need three different diets. This guide explains what fish eat in the wild, what that means for the fish in your tank or pond, how often to feed them and which foods to keep away from them.
- Diet type comes first. Find out whether your species is a carnivore, herbivore or omnivore before you buy food.
- Staple plus variety. A good pellet or flake should be the base, with frozen, live or vegetable foods two or three times a week.
- Less than you think. Most adult fish need one or two small feeds a day, and overfeeding harms fish more often than underfeeding does.
- Temperature rules the pond. Koi and pond goldfish eat heavily in summer, lightly in spring and fall and not at all in cold winter water.
Why mouth shape gives the diet away
You can often guess what a fish eats by looking at its face. An upturned mouth, as on a betta or hatchetfish, means it feeds at the surface on insects. A downturned mouth with barbels, as on a corydoras or a koi, means it forages along the bottom. A sucker mouth means an algae grazer. Large jaws with visible teeth mean a predator. We covered the teeth side of this in our guide to whether fish have teeth, and the same logic applies to diet.
Gut length tells the same story
Carnivores have short, simple guts because animal protein digests quickly. Herbivores have long, coiled intestines to break down tough plant fiber. Goldfish, which lean toward plant matter, have a gut several times their body length and no true stomach. That is why they graze all day in the wild and why one large meal a day suits them poorly.
Carnivores, Herbivores and Omnivores
Carnivorous fish
Carnivores eat other animals. In the wild that means insects, worms, crustaceans, mollusks and smaller fish. In the aquarium it means a pellet with fish or krill listed as the first ingredient, backed up by frozen bloodworms, brine shrimp or mysis shrimp. Bettas, oscars, pike cichlids, most marine predators and nearly all pufferfish fall into this group. Many carnivores will nibble at algae or plants, but they cannot digest large amounts of plant matter and will lose condition on a vegetable-heavy flake.
Herbivorous fish
Herbivores graze on algae, aquatic plants and biofilm. Mbuna cichlids from Lake Malawi, surgeonfish, parrotfish, many plecos and silver dollars sit here. They need spirulina flakes, algae wafers and fresh vegetables, and they need to eat often because plant food is low in calories. Feeding a herbivore a rich, protein-heavy diet causes the bloating and gut problems that Malawi keepers dread.
Omnivorous fish
Most popular aquarium fish are omnivores. Goldfish, koi, guppies, platies, mollies, tetras, barbs, danios, angelfish and clownfish all take a mix of animal and plant foods. A balanced community flake or pellet suits them, with frozen food and a vegetable treat added for variety. The ratio matters: goldfish and mollies lean toward plants, while angelfish and barbs lean toward protein.
What Pet Fish Eat: Flakes, Pellets, Frozen, Live and Vegetables
Flakes and pellets
Dry food is the staple for almost every tank. Flakes float, then sink slowly, which suits surface and midwater fish. Pellets come in floating, slow-sinking and sinking versions sized for everything from nano fish to large cichlids. Read the first three ingredients: fish meal, krill or shrimp for carnivores and omnivores, spirulina or kelp for herbivores. Avoid foods that lead with wheat or corn. Our ranking of the best betta fish food shows how much the quality of a pellet varies between brands.
Frozen and freeze-dried foods
Frozen bloodworms, brine shrimp, mysis shrimp, daphnia and cyclops are the closest most keepers get to a natural diet. Thaw a cube in a little tank water, then feed only what the fish clear in a couple of minutes. Freeze-dried versions keep longer but can float and cause gulping, so soak them first.
Live foods
Live brine shrimp, daphnia, blackworms and microworms trigger a hunting response that no pellet can match, and they are the best food for fry and fussy wild-caught fish. Buy from a clean source or culture them yourself, because live foods collected from ponds can carry parasites. Feeder goldfish are a poor choice for predators: they are low in nutrition and often carry disease.
Vegetables and algae
Blanched zucchini, cucumber, shelled peas, spinach and slices of sweet potato are eaten eagerly by plecos, goldfish, mollies, silver dollars and many cichlids. Weigh the slice down with a fork or a vegetable clip and remove leftovers after a day. Algae wafers and spirulina flakes cover the same need in a cleaner form.
What Popular Aquarium Fish Eat: Species Guide
The table below covers the five fish people ask about most. Each one needs a different diet, and feeding them all from one tub of flakes is where most problems start.
| Fish | Diet type | Staple food | Treats and extras |
|---|---|---|---|
| Betta | Carnivore | Small betta pellets, fish or insect meal first | Frozen bloodworms, brine shrimp, daphnia |
| Goldfish | Omnivore, plant-leaning | Sinking goldfish pellets or gel food | Shelled peas, spinach, zucchini, daphnia |
| Tetra | Omnivore | Micro pellets or crushed flakes | Baby brine shrimp, cyclops, daphnia |
| Pleco | Omnivore, mostly vegetable | Algae wafers, driftwood to rasp | Zucchini, cucumber, sweet potato, occasional bloodworm |
| Cichlid | Varies by species | Species-specific cichlid pellet | Spirulina for mbuna, mysis or krill for predators |
Betta fish
Bettas are insect eaters. In rice paddies they pick mosquito larvae and small invertebrates from the surface, which is why their mouth turns upward. Feed two to four small pellets once or twice a day, with frozen or live food a few times a week. Bettas beg constantly and bloat easily, so portion control matters more than variety. Our guide on how often to feed a betta fish gives a day-by-day schedule, and the full betta fish care guide covers the rest of the routine.
Goldfish
Goldfish are grazing omnivores with no true stomach. They do best on two or three small feeds a day of a sinking pellet or gel food, plus vegetables. Floating flakes make them gulp air, which contributes to the swim bladder trouble fancy goldfish are known for. Shelled peas are the classic fix for a constipated goldfish for the same reason.
Tetras
Neon, cardinal, ember and rummy nose tetras are small omnivores that feed in the middle of the water column on tiny invertebrates and plant matter. Crushed flakes or micro pellets work, but baby brine shrimp and cyclops bring out their color. Their mouths are tiny, so most standard pellets are too big. The best nano fish for small tanks share this need for very fine food.
Plecos
Common and bristlenose plecos are not the algae-only cleaners pet stores describe. They need algae wafers every evening, fresh vegetables a few times a week and, for bristlenose and other wood-eating species, a piece of driftwood to rasp. A pleco that only gets leftover flakes will slowly starve in a clean tank.
Cichlids
Cichlids cover every diet type, which is why the family has filled so many habitats. Mbuna from Lake Malawi are algae grazers that need spirulina-based food. Peacocks, haps and most Central American cichlids are omnivores leaning toward protein. Oscars and pike cichlids are predators. Our guides to African cichlids and the main cichlid fish types break the diets down species by species.
What Pond Fish Eat: Koi Feeding Through the Seasons
Koi and pond goldfish are omnivores that eat worms, insect larvae, snails, algae and plant matter in a natural pond. In a garden pond the food you offer matters, but so does the water temperature, because a koi’s digestion slows as the water cools. Pond keepers feed by thermometer, not by calendar.
Spring and fall: water between 50 and 60 F
Switch to a wheat germ based pellet, which digests easily in cool water, and feed once a day or every other day. Give only what the fish finish in a few minutes. Feeding heavy protein pellets in cold water leaves food sitting in the gut, where it can rot before it digests.
Summer: water above 60 F
This is the growth season. Feed a staple or color-enhancing koi pellet two to four times a day in small amounts. Many keepers add treats such as watermelon, orange slices, shelled peas and earthworms.
Winter: water below 50 F
Stop feeding completely. Koi and goldfish enter a state of torpor, their metabolism drops and they live off stored fat. Food offered now will not be digested. Begin again in spring once the water holds above 50 F for several days in a row.
| Pond water temperature | What to feed koi | How often |
|---|---|---|
| Below 50 F (10 C) | Nothing | Do not feed |
| 50 to 60 F (10 to 15 C) | Wheat germ pellet | Once a day or every other day |
| 60 to 75 F (15 to 24 C) | Staple or growth pellet | Two to three times a day |
| Above 75 F (24 C) | Staple pellet, fruit and vegetable treats | Three to four small feeds a day |
What Wild Freshwater Fish Eat
Insect and invertebrate feeders
Trout, minnows, sunfish, darters and most small river fish live on aquatic insects. Mayfly, caddisfly and midge larvae make up the bulk of the diet, with terrestrial insects that fall onto the water in summer. Fly fishing is built entirely around copying this food source.
Predators
Largemouth bass eat sunfish, minnows, crayfish and frogs. Pike and muskie ambush fish from weed beds, and walleye hunt perch and shiners at dusk. Most predatory fish start life eating plankton and insects and switch to fish as their jaws grow.
Bottom feeders and grazers
Carp, suckers and many catfish sift mud for worms, insect larvae, snails and plant matter. Grass carp eat aquatic plants almost exclusively and are stocked in some lakes to control weeds.
What Wild Marine Fish Eat
Plankton feeders
Herring, sardines, anchovies and menhaden swim with their mouths open and strain plankton through fine gill rakers. The two largest fish in the sea, the whale shark and the basking shark, feed the same way. These plankton eaters support nearly every larger ocean predator, from tuna to seabirds and whales.
Reef grazers and pickers
Parrotfish scrape algae and bite coral, surgeonfish and the unicornfish crop seaweed, and butterflyfish pick coral polyps and tiny invertebrates. Clownfish eat zooplankton, algae and scraps left by their anemone, which is why they take flake and frozen food so readily in a tank. Our clownfish care guide covers their aquarium diet in detail.
Open ocean hunters
Tuna, mahi-mahi, marlin and sharks eat squid, mackerel, flying fish and anything smaller that they can run down. Groupers and snappers ambush fish and crabs from reef ledges. Pufferfish and triggerfish crack urchins, crabs and mollusks with beak-like teeth, a habit that carries over to captive species such as freshwater puffer fish, which need snails to wear their teeth down.
How Often to Feed Fish: Frequency by Fish Type
Feeding frequency depends on the size, age and diet of the fish. The table below gives a safe starting point for healthy adult fish at normal tank temperature.
| Fish type | Feeds per day | Portion guide |
|---|---|---|
| Betta | 1 to 2 | 2 to 4 pellets per feed, one fasting day a week |
| Goldfish | 2 to 3 small | What they clear in 1 to 2 minutes, sinking food |
| Tetras and small community fish | 1 to 2 | A pinch of crushed flake or micro pellets, gone in 2 minutes |
| Plecos and bottom feeders | 1, in the evening | One algae wafer per fish plus vegetables 2 to 3 times a week |
| Cichlids (mbuna) | 1 to 2 small | Spirulina pellets, never bloodworms as a staple |
| Large predators (oscars, large cichlids) | 1, or every other day | A few large pellets or a thawed shrimp |
| Fry | 3 to 5 | Tiny amounts of baby brine shrimp or powdered food |
| Koi, summer | 2 to 4 | Finished within 5 minutes; nothing below 50 F |
The two-minute rule
Feed only what the fish eat in about two minutes, then stop. Most dry food that sinks past the fish and settles in the gravel is never eaten. It breaks down into ammonia and feeds the bacteria blooms behind a cloudy fish tank. If you are unsure, feed less and watch the bellies: a slightly rounded belly after a meal is right, a swollen one is too much.
Fasting days
Skipping food one day a week does no harm to healthy adult fish and gives the gut time to clear. It is standard practice for bettas and goldfish, which are both prone to bloating. Do not fast fry, very small nano fish or fish recovering from illness.
Signs You Are Overfeeding
In the fish
- A swollen belly that does not go down between meals
- Long, trailing waste, which often points to constipation or too much dry food
- Fish that float or sit at odd angles after eating, common in fancy goldfish
- Sluggish, uninterested fish at feeding time
In the tank
- Uneaten food on the gravel an hour after feeding
- Cloudy water, a film on the surface or a sudden algae bloom
- Ammonia or nitrite showing on a test kit in an established tank
- Snail populations exploding
Overfeeding is the most common root cause of poor water quality, and poor water is behind most of the problems in our chart of common fish diseases. Cut portions in half, siphon the gravel and the tank usually recovers within a week.
What Not to Feed Fish
Bread, crackers and other human food
Bread is the most common bad food given to pond fish and goldfish. It swells in the gut, has almost no nutrition and fouls the water. Chips, rice, pasta, cheese and processed meat are no better. If you want to hand-feed, use pellets, peas or earthworms.
The wrong type of food
- Protein-heavy food for herbivores. Bloodworms and beef heart cause bloat in mbuna cichlids and silver dollars.
- Vegetable flakes for carnivores. Bettas and puffers cannot digest them and will slowly lose condition.
- Feeder goldfish and wild-caught live food. Both are common sources of parasites and disease.
- Food that is too large. Standard pellets can lodge in the throat of tetras, rasboras and other nano fish.
- Stale food. Dry food loses its vitamins within a few months of opening. Buy small tubs and keep the lid sealed.
What Fish Eat FAQs
What do fish eat in the wild?
Wild fish eat whatever their habitat and mouth shape allow. Small freshwater fish take insects, larvae, worms and algae. Predators such as bass, pike and tuna eat other fish, crayfish and squid. Reef grazers like parrotfish and tangs scrape algae, while filter feeders such as herring and whale sharks strain plankton from open water.
What do fish eat in a tank?
Most aquarium fish do well on a quality flake or pellet made for their diet type, with frozen or live foods such as brine shrimp, bloodworms and daphnia a few times a week. Herbivores and omnivores also need vegetable matter from algae wafers, spirulina flakes or blanched zucchini and peas.
How often should I feed my fish?
Once or twice a day is right for most adult aquarium fish, giving only what they finish in about two minutes. Fry need three to five small feeds. Large predators can be fed once a day or every other day. Koi eat two to four times a day in summer but nothing at all once water drops below 50 F.
Can fish eat bread?
No. Bread swells in the gut, offers almost no nutrition and clouds the water as it breaks down. It is one of the most common causes of bloating in pond goldfish and koi. Use a proper pellet instead, and offer peas or leafy greens if you want to hand them a treat.
How long can fish go without food?
Healthy adult fish can usually go a week or more without food, and many keepers skip one day a week on purpose. Fry and very small fish such as nano tetras have less reserve and should not go more than a day or two. For a vacation longer than a week, use an automatic feeder or ask someone to feed small portions.
What vegetables can fish eat?
Blanched zucchini, cucumber, shelled peas, spinach, romaine and slices of sweet potato are the usual choices. Plecos, goldfish, mollies and many cichlids graze on them readily. Remove any uneaten vegetable after 24 hours so it does not foul the water.
Do fish eat algae?
Many do. Plecos, otocinclus, Siamese algae eaters, mollies, tangs and parrotfish all graze algae as a major part of their diet. Algae alone is rarely enough in a clean tank, so these fish still need algae wafers or vegetables to stay in condition.
Final Thoughts
Match the food to the fish
So, what do fish eat? Everything from plankton to other fish, depending on the species. The job of a fish keeper is to work out which of those diets the fish in front of them evolved for, then provide it in small portions with some variety. Get the diet type right, feed less than feels natural and watch the water temperature if you keep a pond. Most feeding problems disappear once those three habits are in place.
