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Exploring the Diets of Wild Fish: Get the Facts

There are thousands of different species of fish, each with its own preferences when it comes to habitat, climate, and diet. Fish can be herbivores, carnivores or omnivores. To find out what do fish eat in the wild, first, it is essential to consider their natural habitat.

Freshwater Fish

Freshwater fish are those that live in freshwater or water with a low amount of salt content. The environment in which these fish live differs significantly from saline environments and hence their diet also varies greatly.

Some common freshwater habitats are rivers, ponds, and lakes. Some common freshwater fish species are trouts, catfish, swordtails, and so on.

Fish usually have quite diverse diets and are experimental when it comes to food. This determines what fish eat in the wild.

Most fish try to eat most things that come their way. If they taste a particular substance and find it to be edible, they often go ahead and eat it.

As such, freshwater fish eat many different kinds of foods, starting from algae and other microorganisms to small insects to other fish as well.

They require around half of their diet to consist of protein but also need to consume other food groups such as carbohydrates and fats.

All the different food groups together ensure their growth, warmth, and energy. Let’s see what do fish eat in the wild in freshwater habitats.


Shark feeding

Kokanee is a species of fish that is very close to the sockeye salmon that we commonly know as salmon. Though the sockeye salmon breeds in freshwater, it migrates to the sea eventually.

Author Note: On the other hand, the kokanee, also known as the Kennerly’s salmon, breeds in freshwater and then lives out the rest of its life cycle in freshwater as well.

Kokanee has very fine structures on their gills known as gill rakers that help them strain small foods from the water.

A large part of their diet consists of zooplankton that they find from the water using their gill rakers. Kokanee fish follow the zooplankton to the depths of the water according to changes in weather as well.

However, their diet is not entirely limited to zooplankton and they also eat other small insects, plants, and some other organisms such as small shrimps. They also eat small insects from outside the water by jumping out occasionally.

Rainbow Trout

Rainbow trout is a species of trout that mostly lives in cold freshwater habitats. Some of the fish of these species live entirely in freshwater, while some also migrate to the ocean.

Rainbow trout are carnivorous in nature as they require a high amount of protein in their diet. They avoid eating vegetation and mostly tend to consume small organisms like insects and beetles.

Sometimes, rainbow trout may even eat small rodents. They also eat smaller fish, including kokanee fish.

Since they have a carnivorous diet, fish eggs and flies are often used as bait while catching rainbow trout.


Walleye is a freshwater fish that can usually be found in cool waters. It is a common choice for those who fish as a sport. Walleye fish, like many other species, adapt their diets to what is available.

Walleye are primarily carnivorous and their preferred kind of food is other smaller food. Smaller fish are often the most commonly available food in the dark and cold waters that walleye tend to live in.

Some of the most common fish that walleye fish like to eat are yellow perch and minnows.

Other than smaller fish, they also eat other organisms such as leeches and insects as well as large invertebrates.

Depending on what is available, they might also eat snails, frogs, mudpuppies and other small animals that they find in the water when there are not enough fish and insects.

Northern Pike

hawkfish on the coral

The northern pike, commonly known as the pike, can be found in freshwater habitats as well as brackish water habitats. Brackish water refers to water that has a higher salt content than freshwater but not as much salt as the ocean.

The northern pike is actually named after the weapon pike which is essentially a spear with a long pole. The fish resembles a weapon because it is a predatory fish that has an entirely carnivorous diet and eats nearly any other organism that it can find in its habitat.

Author Note: The northern pike usually lives in sluggish water with a lot of vegetation inside, which helps the fish hide and ambush its prey.

They eat smaller fish such as bass and perch as well as animals that they find in the water such as frogs and snakes. Larger pikes also eat other smaller pikes.

Marine Fish

Marine fish or saltwater fish are those fish that live in water with a high salt content such as seas and oceans. There are thousands of marine fish, each with different habitats and dietary habits.

Marine fish can be herbivorous, carnivorous or omnivorous. According to the adaptations they have made to their diets, there are significant differences in the bodies and systems of herbivorous and carnivorous fish.

Since plant material has a large amount of cellulose and fiber, herbivorous marine fish have a very long digestive tract that contains a large number of bacteria.

This bacteria is kept alive by the conditions inside the digestive system of the fish and is crucial for the digestive system of the fish as well.

The bacteria help the fish digest the food and release carbohydrates to give energy to the fish. The fish then further digests the bacteria to get the protein it requires in its diet.

On the other hand, predatory fish have smaller digestive systems which use certain enzymes to digest the food.

Though herbivorous fish often experiment with food depending on what is available, carnivorous fish almost exclusively eat other fish and smaller organisms and altogether avoid any form of plants or algae.

Let us see what fish eat in the wild in marine or saltwater habitats.


Clownfish are marine fish species found chiefly in warm waters of the Indian Ocean, Pacific Ocean, the Great Barrier Reef and so on.

They are also known as anemonefish because of the symbiotic relationship they have with sea anemones, a predatory animal that resembles the anemone plant.

Clownfish have an omnivorous diet which means that they eat both plants and other fish and so on. Clownfish are quite diverse and exploratory when it comes to their diet and they eat algae, smaller fish, insects, small invertebrates and so on.

The clownfish is hosted by the sea anemones, which helps it hide and protects it from predators. The clownfish also depends on the sea anemones for food as it eats undigested food from the food.

On the other hand, the excreta of the clownfish helps in the nutrition of the sea anemone.

Green Chromis


The Green Chromis, also known as the Chromis Verdes is a form of damselfish that is known for its stunning bluish-green color. It is a marine fish found mostly in tropical and subtropical oceans and seas.

The Green Chromis is known to be hardy and highly adaptable and will eat almost anything that is available in its habitat by scavenging around for food. The fish has an omnivorous diet.

Author Note: They eat plant matter such as algae and they also eat planktons, shrimp, many other smaller fish and insects and so on.

Since they eat almost anything that is available to them, they are a common choice for breeding in aquariums, especially by beginners. However, they must be fed often during the day and one must ensure to give them enough food with protein.


Tuna is a predatory fish found in saltwater habitats. The tuna can regulate its body temperature to be higher than the surrounding water and can hence survive in habitats of different temperatures.

Tuna is a predator and has an agile and streamlined body that allows it to move through the water fast.

Tuna is a carnivorous fish but different species of tuna have different preferences when it comes to food. For instance, the bluefin tuna is an aggressive predator that eats smaller tuna, mackerel, squids, eels and so on.

The yellowfin tuna is known to hunt in deeper waters and feeds on much larger prey such as dolphins, squids, lobsters, octopuses, and so on.

Parting Thoughts

There is no simple answer to the question of what do fish eat in the wild. There is a wide variety of fish that live in different kinds of habitats around the world. Some live in freshwater habitats, some in brackish water and some in marine waters.

In each of these habitats, there are different kinds of fish that have herbivorous, carnivorous, or omnivorous diets. Different fish have adapted their bodies according to the different diets that they follow.

Some freshwater fish are kokanee, rainbow trout, walleye, and northern pike. Some marine fish include clownfish, Green Chromis, and tuna.

We hope you enjoyed this article on what do fish eat in the wild.

Happy Hunting!


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