How Fish Feed

Different species of fish have their own specific feeding habits. The jawless fish (the Agnathans) have limited options for feeding since they don't have jaws that move up and down. Their only tool for eating is a sharp set of teeth. The hagfish, which belongs to this group, is known to feed mainly on dead animals.

Fish found in shallow waters mainly feed on shrimp, crabs, and other crustaceans. The diet of fish from deep waters has great diversity. Some of these fish are omnivores and feed on aquatic animals including crustaceans, worms, and smaller fish. The diet of fish is classified on the basis of their feeding habits.

Fish Diet: What Fish Actually Eat

The dietary habits of fish differ from one species to another, and it is very difficult to come up with a detailed list of every marine plant and animal they eat. While some species are specifically herbivorous or carnivorous in nature, others are omnivorous and eat both plants and animals.

  • Algae: Algae form the diet of herbivorous as well as omnivorous fish. Omnivorous fish eat macroalgae along with crustaceans, for which they have to go hunting.
  • Sea Grasses and Algae: Fish that feed on algae and sea grass are totally herbivorous.
  • Algae and Detritus: Coral slime, the solid waste matter released from fish, and organic matter that accumulates over time on the sea floor make up detritus. This detritus forms the diet of many types of fish.
  • Sponges: Omnivorous fish like Angelfish feed on sponges. Sponges form the bulk of their diet.
  • Plankton: Plankton (which includes different types of fish, shrimp, copepods, mysids, and amphipods) is a supplementary part of the diet of many fish.
  • Mixed Diet: Omnivorous fish that feed at the bottom of the ocean have a mixed diet. They are opportunistic and survive on almost any food they find near the sea floor, including worms, small fish, crustaceans, and almost everything edible.
  • Other Fish: A few species of fish prey on other fish by means of ambush.
  • Crustaceans: Shrimp, crabs, and other crustaceans form a major part of the diet of some fish species.
  • Invertebrates: Small invertebrates eaten by generalized invertebrate feeders include snails, sea urchins, worms, and starfish. Sedentary or sessile organisms like corals, polyps, and clams also form part of this diet.
  • Parasites: Some fish feed on the parasites of other fish species.
A variety of fish swimming in the ocean, showing the diversity of aquatic life
Fish show an enormous variety of feeding strategies, from grazing on algae to hunting other animals.

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Diet of Different Kinds of Fish

While the section above covers the general types of things fish eat, here is information about the specific diet of some of the most popular species in the world.

  • Sharks: Sharks feed on seals, smaller fish, plankton, and also their own species.
  • Dolphins: Dolphins feed on a variety of fish, but the main diet includes squids and mackerel. Mackerel are preferred over squids because they contain a large amount of body fat. Dolphins also feed on cods, herrings, and plankton.
  • Salmon: Salmon are carnivores and feed on small invertebrates and zooplankton while they are young. As they get bigger, salmon start eating krill, herrings, and other small fish. Salmon raised on farms are fed a mixture of different types of fish.
  • Piranha: Piranhas are carnivorous and feed on a variety of aquatic creatures. Crustaceans, mollusks, insects, and other fish form the piranha's diet. They may also eat amphibians, dead birds, and rodents.
  • Trout: Trout is basically a carnivore that feeds on different fish (mainly Cisco and Whitefish), shrimp, and small-sized mammals. Trout is also known to feed on plankton, which makes it an omnivore.
  • Eel: The main diet of eels includes crabs and smaller fish. The eel also feeds on other invertebrates apart from crabs.
  • Ray Fish: Ray fish are omnivorous. They feed on shell-covered creatures like snails, oysters, clams, and crabs. Some ray fish also consume plankton.
  • Jelly Fish: Jellyfish don't have a developed digestive system. They eat food that is attached to their tentacles. Generally, zooplankton and small fish form the diet of jellyfish.
  • Scorpion Fish: This fish uses the ambush technique and preys on smaller fish.
  • Gold Fish: Goldfish are omnivores and their diet ranges from plankton and detritus to worms, insects, and larvae.
  • Koi Fish: Koi fish feed on lettuce, algae, peas, and even fruits. Koi raised in aquariums are not fed a high-protein diet since it causes digestive problems. Crustaceans also form a major part of their diet.

Frequently Asked Questions

What do hagfish eat?

Hagfish feed mainly on dead animals, they are jawless and cannot actively chase prey.

Are all fish carnivores?

Most fish are carnivorous, but some (like koi and certain reef fish) are herbivores or omnivores.

What do sharks eat?

Sharks feed on seals, smaller fish, plankton, and sometimes their own species.

What do pet fish eat?

Pet fish are fed flakes, granules, and pellets. They can also eat vegetable matter like raw potato, beans, peas, and zucchini. Sponges and spirulina algae are sometimes given in frozen form.

A red-bellied piranha showing its sharp teeth, an example of a carnivorous fish
Piranhas are carnivores that eat crustaceans, mollusks, insects, other fish, and sometimes dead birds and rodents.

Pet Fish Diet

Pet fish are given food in the form of flakes, granules, and pellets. Vegetable matter (raw potatoes, bits of beans, peas, zucchini, and similar items) can also be fed to pet fish. Sponges and spirulina algae are some of the foods given to fish in frozen form.

A bright orange koi fish eating plants near the surface of a garden pond
Koi fish are omnivores that enjoy lettuce, algae, peas, and even fruit, but too much protein causes them digestive trouble.

Every Fish, Its Own Menu

The diet of fish is largely shaped by the environment in which they live. Most fish are carnivorous, while a few are completely herbivorous. Different types of fish each have their own specialized feeding habits, a fact that shows how well fish have adapted to pulling rich nutrients from the aquatic world they call home.

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