What do Fish Eat in the Wild?

The answer to the question “What do wild fish eat?” is a rather complicated one. It depends on where fish live and whether they are vegetarian or picky about their dinner.

Fish eat various food, from algae and plankton, through aquatic plants and detritus, to crustaceans, mollusks, and other fish.

Some fish would be primarily vegetarian, and others would eat whatever they can catch, like aquatic and terrestrial insects and even small mammals.

How to Know What Fish Eat

The answer to the question about the fish diet, although rather complex, is also essential from the angler’s point of view. Knowing what the fish eat will better the chances of catching. 

Like the popular saying within the fly-fishing community, “match the hatch” can also be translated to other fishing techniques. Any angler counting on success should present the right lure or bait to the targeted fish. 

Because of a large variety of fish, there is no way of knowing for sure what each fish eats, but most fish are similar to each other in one way or another.  

Some bottom feeders would also be predators, but usually, the build of the fish body may be one suggestion as to what food they prefer to eat. 

Another suggestion as to what fish eat would be the habitat they live in. Whether they stay at the bottom or hide between the reeds would help the angler better understand the fish feeding habits.

What do Wild Fish Eat?

Most fish diets consist of at least 50% protein, but algae is another smart food source, thanks to its fats and carbohydrates. Like people and other animals, fish need protein for strength, carbs for energy, and fats for warmth.

Keep in mind that the environment is the most important factor in a fish diet. There are over 33,000 known fish species worldwide, and what fish eat depends on where they live. Available food sources differ throughout ponds, streams, rivers, lakes, and oceans across the globe.

For that reason, most fish eat insects and smaller marine creatures they can safely swallow and digest, although some species are pickier than others.

We can classify wild fish as freshwater or saltwater. 

Freshwater fish live in ponds, lakes, rivers, and streams and usually feed on smaller freshwater species. It may include minnows, leeches, worms, insects, weeds, and algae

Saltwater fish in seas and oceans tend to feed on similar food sources to their freshwater cousins, but since the life in the oceans can be a little bit more diverse, they can also indulge in coral, urchins, and squid.

What do Fish Eat in the River?

What do Fish Eat in the Wild?

There is a multitude of species in rivers. Depending on the geographical position and elevation of the specific river, the species vary greatly, and so does the food they consume. In warmer and slower rivers, there would be more plankton, crustaceans, and aquatic plants. In faster mountain rivers, fish would usually feed on insects, larvae, and other fish.

Even though there is an abundance of species inhabiting rivers, they generally come under two main groups. 

Predators

Predatory fish in the river usually start as omnivores or even herbivores. When they hatch, and the yolk sac gets empty, they are still too small to hunt. Sometimes in that situation, they tend to turn towards zooplankton. 

Some of the predatory fish species, like northern pike, will start by eating planktonic crustaceans, i.e., daphnia. As they grow bigger, they start eating bigger prey, like small crustaceans, insects, leeches. When they reach around 2 inches, they start feeding on small fish. 

The big specimens are known to eat frogs, fish, mice, ducklings, crayfish, and if the food is scarce, they turn on each other in the act of cannibalism.

Other fish, like trout, in their fry stage, will feed primarily on zooplankton until they are big enough to start eating insect larvae. With growth, the food of most trout species doesn’t change much.

Some of the more docile species, like rainbow trout, will be content to eat anything they can catch, like crayfish, insects, fish eggs, and small fish. 

Others, more aggressive, like char or brown trout, would actively pursue other fish species, like shad, minnows, and sculpin, and won’t stop from eating mice or baby birds falling out of a nest.

There are also seven species of Pacific salmon and one Atlantic salmon. Those species live in the river for a short time before they migrate to the sea and after they come back for spawning.

Their food as parr (little salmon with camouflage stripes) usually consists of terrestrial insects. As smolt (young salmon migrating to the sea at the age of 2-3 years old), they move to bigger prey, like mollusks, crustaceans, and small fish.

When the salmon come back to the river for spawning, they usually don’t feed much, but when they do, their diet usually comprises of land and water insects and worms.

Bottom Feeders 

Bottom feeders are not necessarily feeding on the bottom of the river. 

Some anglers use this term to describe many fish species, like carp, or bass, which are typical bottom feeders (although bass is also a predatory fish, and carp is an omnivore). 

But it can also describe fish dwelling in all layers of the rivers but are primarily herbivores or omnivores.

Some fish will prefer to stay at the bottom, most of the time, and feed on the surface when the opportunity arises. 

One of those species is catfish. The catfish is an omnivore, which means it feeds on anything it can find. They prefer to stay at the bottom and consume anything they can eat, i.e., plant matter, seeds, insects, mollusks, and small fish. 

On rare occasions, catfish are known to come up to snatch a duckling from the surface or a pigeon from the shore. There are reported incidents of catfish eating turtles and even small mammals, like an armadillo or a beaver.

Not precisely a bottom feeder either, silver carp is a filter feeder. It uses its sponge-like gill rakers to filter water and pick up any parts of phytoplankton and zooplankton.

One of silver carp’s cousins, the grass carp, is herbivorous. It eats primarily submerged aquatic flora, like coontail, hydrilla, and nitella.

There are also species mentioned before, which live in all layers of the river and eat anything they can fit in their mouths. In that group, anglers usually put panfish, like bluegill or crappie.

They feed primarily on insects, larvae, shrimp, crustaceans, and small fish. However, it’s not uncommon to see them eating algae and aquatic vegetation when other food is scarce.

What do Fish Eat in the Lake?

What do Fish Eat in the Wild?

Just like with rivers, thousands of different fish species inhabit lakes. And just as position on the map determines what fish live in which river, the lake-dwelling fish may vary and be divided by the type of food they eat.

In bigger and deeper lakes, there may not be as much aquatic flora for the fish. More of the species there would consume food like crayfish, shrimp, and other fish. In smaller lakes and ponds insects, plankton, and plant matter seem to be more popular fish food sources.

Predators

Lake predators don’t seem to be too fussy about their food. 

After they hatch, predatory fish, like walleye, usually start eating small invertebrates like copepods and cladocerans. When they grow bigger, they begin mainly preying on yellow perch and minnows, which seem to be their favorite food, although many other species are also on their menu.

When the food sources are dwindling, the walleye turns its mouth to mudpuppies, crayfish, snails, frogs, and small mammals.

When predatory fish, like muskie, reach a specific size (generally more than 1.5 inches), they begin preying on other fish, like lampreys, suckers, whitefish, minnows but won’t turn from muskrat, mice, frogs, and ducks.

For muskies, the size of the dinner usually doesn’t matter too much. They’ve been known to eat prey reaching almost 2/3 of the length of their bodies. 

They often swim with a piece of their food sticking out of their mouth, waiting for the part in the stomach to digest before finishing their meal.

Another predator fish is bass. Largemouth, smallmouth, or spotted, their primary food is any fish that doesn’t try to eat them first.

When they are small, they usually eat insects, zooplankton, tadpoles, and minnows. The older the bass gets, the more dishes are on its menu. Young bass would also eat worms and leeches. 

As opportunistic feeders, the adult bass would eat anything that swims in front of them. Bass will eat snakes, frogs, shrimp, shads, eels, ducks, or even another bass if the food is scarce.

In fact, many freshwater predatory fish would eat their own kin if the food situation is tight.

Yellow perch is also one of the fish that, when pressed, would eat smaller yellow perch. When the food is abundant, they prefer to eat shrimp, crayfish, fish eggs, and other small fish.

As little fish, yellow perch grows up on an animal matter, starting with zooplankton, moving to invertebrates, like midges and mosquitoes.

Yellow perch is also the favorite food of northern pike, bass, sunfish, crappie, and walleye.

Bottom Feeders

The best known true bottom-feeders are common and mirror carp. They would suck up anything that litters the bottom of the lake. Carp eat aquatic worms, crustaceans, mollusks, algae, plant matter, and detritus.

Carp will not disregard any fish carcass they can find, as well as fish eggs. They often rise for flies from the water surface.

Another well-known bottom feeder is lake sturgeon. This ancient-looking fish is relatively rare and can live long years. The lake sturgeon prefers fresh food over any dead organisms and decomposing matter.

Their feeding method is to stir up the sand, mud, or gravel on the bottom and, using their vacuum-like mouth, suck up the floating debris. Sturgeon expel all sandy particles and muck through their gills and keep and consume picked up food.

And that can be anything that skitters on the bottom, starting with insects and larvae to crayfish, snails, mollusks, and leeches. They won’t say no to small fish and worms either.

Even though they don’t spend much time at the bottom, shad is not a predator. The threadbare shad eats only plankton near the surface of the water. They are a favorite food of fish like bass and catfish.

The gizzard shad has a little bit more diverse diet. Gizzard shad also eat zooplankton, and when it gets bigger, it adds detritus to its menu. 

What do Fish Eat in the Ocean?

What do Fish Eat in the Wild?

The famous saying “plenty fish in the sea” can be taken literally because there are around 20000 species of fish in the ocean, and sea fishing can be like a lottery. You can catch the popular, the weird, and the rare fish using one bait.

But just like in rivers and lakes, we can segregate ocean fish into different groups based on their favorite meals.

Some of them would prey primarily on other fish and sea creatures. Others would peacefully swim around, grazing on algae, coral reefs, or picking small mollusks.

Omnivores

There is plenty of species that anglers and commercial fishers pull out of the water each day, and not all of them are predators. Omnivorous and bottom-feeding fish make up most of the population of the ocean. 

Some fish would live and feed in schools, like mackerel and sardines. The mackerel, one of the more popular commercial fish, lives in the pelagic zone. They stay in the middle between the surface and bottom of the ocean.

The favorite food of mackerel are copepods, shrimps, and squids. When mackerel is small, it feeds on zooplankton, but when it grows big enough teeth, it will also eat small forage fish, like sardines.

Sardines are common fish, often canned, smocked, and pickled. But while still in the ocean, they feed only on plankton. That includes zooplankton and phytoplankton alike. 

Some of the omnivorous species pulled by anglers, like red snapper, reside close to reefs but do not usually feed on reef creatures, like crustaceans or invertebrates.

Surprisingly, red snapper feeds mainly on creatures dwelling in the muddy bottom, primarily on fish like pinfish, pipefish, cusk and snake eel, pigfish, anchovies, and sea robins.

Another reef fish caught by anglers, and one of the prettiest ones, are parrotfish. Parrotfish are primarily herbivores. Over 90% of their diet is made out of algae covering the coral.

They tear chunks of coral, and after digesting the algae and any other soft tissue, they poop ground coral out as the white sand. 

One of the smaller relatives of cod, haddock, is getting more and more popular by fishermen. This small-mouthed fish spends most of its time at a depth of over 200 feet feeding on sea urchins, sea stars, fish eggs, worms, crustaceans, and sand dollars. 

However, haddock comes closer to the surface in the spring, where catching it becomes very easy. During that time, they feed primarily on small fish, like herring.

Predators

Even though there is plenty of predatory fish in the ocean, they make up only 10% of fish in the sea, and most are at risk of extinction from overfishing or dwindling food sources.

Out of all the fish living in the open ocean with deep waters, most of them are predators for a simple reason. There is not enough light reaching the bottom to produce any plant matter, and the temperatures are very low. 

There are, however, some species of fish living closer to the shore that dwell on the bottom. One of them would be prized halibut.

As a flatfish, halibut lives and feeds mainly on the bottom of the sea. Among its primary food sources are octopus, crab, clams, lamprey, cod, pollock, rockfish, herring, and other halibut. 

When halibut hatch, they look like any other fish, with one eye on each side of the body and swimming upright. At that stage, they feed on plankton and small shrimp-like creatures, like euphausiids.

Another example of a bottom-feeding predator is the ever-popular cod. Although not a flatfish, cod spent most of its time feeding on the bottom of the sea.

Their primary food is sand eels, whiting, squid, crab, lobster, haddock, worms, mackerel, herring, and often small cod.

One of the most notorious predators in the sea is a shark. But not many people know that three species of shart would feed primarily on plankton. Those are basking, whale, and megamouth sharks. 

The rest of the shark species are carnivorous. They would use different techniques to catch their food, and some of them, like whitetip reef sharks, would hunt in packs.

Some sharks are known to eat their prey whole. They would usually feed on smaller fish, mollusks, and crustaceans.

Like the well-known great white, others would attack their prey and tear pieces out of their carcasses. Young great white sharks would usually eat fish, like tuna, rays, other sharks, but also sea otters, seabirds, and seals.

When the sharks grow bigger and their jaws get stronger, their menu widens to include dolphins and sea turtles.

Sharks won’t say no to scavenging. They are often seen tearing pieces of flesh from whale carcasses.

Like swordfish or sailfish, some billfish species would eat primarily crustaceans, squid, and small fish. Similarly, to reach the impressive sizes they are known for, tuna eat mainly smaller fish, squid, eels, and crustaceans.

Occasionally they would also filter-feed on zooplankton and, even though they are predatory fish, they will nibble on kelp.

Mahi-mahi would, in turn, eat juvenile tuna and billfish on top of other fish, like jack crevalle and pompano, invertebrates, aquatic larvae, and bottom-living species. 

Groupers would keep to the bottom of the ocean and usually eat small fish, octopuses, and crustaceans. Some species ambush their prey, and others are actively chasing their food.

Curiously, the biggest of groupers, goliath grouper, feeds primarily on crustaceans, mostly crabs, but will also consume some slow-moving fish species like burrfish, catfish, and toadfish.

When salmon are in the ocean, they usually feed on a wide variety of prey, such as capelin, Atlantic herring, sand lance, barracudina, and lanternfish. They also consume amphipods and euphausiids, squid, octopus, and worms to top up their diet.

What do Fish Eat in Winter?

What do Fish Eat in the Wild?

During winter, water in rivers and lakes drops the temperature, some freezing over, which lowers the number of available food sources for fish. 

Some of the fish species in rivers like trout would migrate to slow-moving parts in search of deep pools, where they can find food and refuge.

During the winter months, trout metabolism slows down, and digestion lasts longer. Because the number of invertebrates drops down, trout eats mostly drifting insects, like midges and mayflies. 

Like few species of catfish, some fish species from lakes would move to the lower parts of the water body to stay in stasis, often burying themselves in the mud. They would then not feed at all, rather wait for the warmer weather.

Other species, like smallmouth bass, would slow their metabolism and life functions, coming into semi-stasis. They would still feed on anything they can catch without too much effort, but the food intake is minimal. 

Some species, like yellow perch, would increase their activity to stay warm and aerated. Because food is scarce in the winter months, yellow perch would eat fish that can fit in their mouths and sometimes try to eat the ones their own size.

Out in the open ocean, the water temperature doesn’t change much. Deepwater fish continue to feed as usual, without much change. 

Close to the shore, where winter months affect the water temperature, some fish, like herring, decide to follow the warm current and migrate south. Others, like flounders, move to deeper parts of the ocean.

Few species, like striped bass, would stay in the same place for the winter, group together in slow-moving schools, and feed whole year-round. Their favorite food is lobsters, crabs, clams, mussels, worms, squid, and whatever small fish species are left after “great winter migration” south.

Conclusion

Wild fish feed on a wide variety of food, depending on where they live and their physical features. The key food sources for wild fish include invertebrates, zooplankton, aquatic plants, crustaceans, and other smaller fish

Most small fish have little protection against larger predators, so they are usually snapped up by bigger creatures such as sunfish, sturgeon, snapper, and bass.

When heading out fishing, it’s always a good idea to bring live baits that fish usually eat in the wild, like minnows, crayfish, shrimp. 

You can’t go wrong with worms or leeches for most recreational fishing, as most wild fish will snap up these food sources if they find them.