What do fish eat?

In this blog post, we will answer the question “What do fish eat?” and learn more about fish diets and the best option for feeding your fish in the aquarium.

Have you ever wondered what fish eat? Different species feed differently and can be carnivores, herbivores, omnivores, etc. which does not mean they have a strict diet in the river or ocean.

What do fish eat? 

Fish diets vary with their habits and biological characteristics. A fish can eat smaller fish, crustaceans, molluscs, larvae, eggs, algae, plants, and biological waste, or detritus.

The factors that determine the type of food eaten by fish are: availability of food, the spatial distribution of fish and food in the environment, ability to camouflage fish (predator) and food (prey), mobility and escape ability of prey, abiotic factors of the environment: temperature, pH, water turbidity, habituation of fish to certain types of food.

The feeding of animals in the wild is highly dependent on the availability or scarcity of certain food types. At home, we can ensure a balanced diet continuously with commercial rations and supplements.

Feeding habits and the importance of a balanced diet

The importance of food for heterotrophic creatures is that they are not capable of generating their own energy. Unlike plants, fish do not produce their energy. They rely on the ingestion of certain substances to obtain the energy and nutrients required by their bodies.

The important nutrients for fish health include proteins, fats, vitamins and minerals. The most important macronutrient for fish, protein, is essential for tissue development and regeneration.

Each species of fish has specific protein requirements that must be included in compound feeds (rations) formulated specifically for each species of fish according to its dietary preferences to ensure the proper development of the animal. Today, fish nutrition is a booming field and we now know that the amino acid profile of a food is a crucial factor in evaluating the quality of food, even more important than the protein content of the food.

The reason for this is that fish do not have specificity for built protein, but a need for certain amino acids in specific ratios. This concept is easy to understand if we make an analogy to a Lego. Amino acids are the building blocks that make up the proteins in the body. If we consider a specific Lego building, we will need a certain number of different Lego blocks in a specific ratio to build it. If we lose one Lego block, the building will never be complete, even if we try to combine other Lego blocks. In addition to these energy sources, fish also need vitamins and minerals to fully develop.

Vitamins and minerals are involved in various metabolic processes that regulate the functioning of the body. Thus, when you think about what fish eat, most of them rely on micro and macronutrients to sustain themselves.

Both micro and macronutrients are obtained from different sources of food. Fish can be:

–       Carnivorous;

–       Herbivorous;

–       Omnivorous;

–       Planktophag;

–       Bentophagous/Detritivores.


Carnivorous fish are fish that feed preferentially on animal protein. They feed mainly on other animals, such as crustaceans, amphibians, insects and smaller fish. They can also supplement their diet with some other type of food. Carnivorous fish developed hunting techniques. Some species developed very specific foraging behaviours, for example, high-speed chasings or camouflage.


Herbivorous fish feed, preferentially, on the protein of vegetable origin, and commercial rations have higher fibre content, like plants, as well as some algae.


Omnivorous fish are fish that feed on any type of food, animal and vegetable origin. They feed on different classes of food, being able to obtain proteins from both plants and small animals. 


Plankton is an excellent source of nutrients for many fish species. Some may eat only phytoplankton and others prefer zooplankton. They normally do not have teeth and may present a big number of gills. These fish species are sometimes called filter feeders.


As the name suggests, they feed on benthic material. It can be benthic organisms such as insect larvae, molluscs and other invertebrates, They can also feed on various organic detritus, such as faeces from other animals. 

What about my pet fish, what does it eat?

An aquarium can be a good option for those who do not have a lot of time to take care of a pet. However, some attention is needed when considering what to feed your fish. 

Each fish has specific feeding behaviour that needs to be considered when choosing the right rations. There are fish that feed on other animals. In these cases, the food may consist mainly of animal protein. Unlikely herbivores that require vegetable protein.

Commercial rations

Indicated to be the basis for feeding tank fish, the ration can be found in versions for omnivorous, carnivorous fish and even developed especially for popular species.

Surface, medium or aquarium bottom rations?

Before choosing the type of food, it is important to know that they can be placed at different points in the water column. That is why it is important to know where your fish species most live and eat. 

Some brands develop food for specific needs and life stages. Examples of this are the rations that help to enhance the colour of the fish. It is important to highlight that, in addition to observing nutritional needs, it is also necessary to be aware of the way each species feeds. Different fish species have different mouth shapes and positions, and teeth. 

To meet these characteristics, there are a variety of types of fish food:

–       Flakes;

–       Pellets;

–       Tablets;

–       Sticks;

–       Wafers;

–       Chips;

–       Freeze-dried;

–       Natural/Live food;

– Holiday rations.


Flakes are a good choice for almost all aquarium fish species. At first, they float, then they start to sink and dissolve. In the end, food fish are on the bottom of the aquarium. Thus, the entire water column is covered with flakes. Even the benthic species are fed by flakes


Pellets are recommended for forage fish in the middle of the water column and for those that feed on the bottom.


They can be placed on the bottom or attached to the tank glass. They are ideal for fish that usually eat in the middle or at the bottom of the aquarium.


Sticks are the ones specific for surface feeders, medium to large-sized fish.


This type sinks very fast and it is a good deal for bottom feeders and crustaceans. 


Chips have a similar shape to potato chips, slice format. They were originally planned for larger species, however, smaller species do not face any issue when eating this type of fish food.


Freeze-dried food fish is in the middle between natural and artificial food. It is fully dry, so it is free of water. The nutritional content remains the same in each of the items used. It can be based on crustaceans and zooplankton.

Natural/Live food

Natural foods are the items your fish would eat in nature. This includes living organisms. From algae and aquatic plants to krill and shrimp.

Although it is not recommended to use them as a food base, you can offer some live foods such as larvae and small crustaceans to complete the diet and specifically enrich the environment of carnivorous fish.

To ensure the safety of the ecosystem, it is important that any food you add to the aquarium has been purchased from a specialist retailer and that the recommended hygiene measures are followed.

Otherwise, you could contaminate the aquarium and put the lives of your fish in danger. Remember that live food alone is not enough to ensure complete nutrition of the fish with all vitamins and minerals.

Holiday rations

Holiday rations have a similar composition to the others. However, they are made in capsules that dissolve over the course of days so that the food is delivered to the fish. This type can last up to 15 days.

When choosing this type of food, it is important to consider the size of the aquarium and the number of fish. Also, remember that this type of food should not be used frequently as it contains small amounts of nutrients.


In this post, we have explained what fish eat and what is the best food for your ornamental fish. We have outlined the foraging behaviour of fish and also described some of the types of food.

Frequently Asked Questions (FAQs): What do fish eat?

What do river fish eat?

River fish, like many other fish species, feed on larvae and insects, depending on the species, of course. Most fish are carnivores. However, there are also herbivores and detritivores.

What do fish eat besides rations?

When the fish are larger, you can offer frozen or live foods such as small worms, daphnia and brine shrimp two or three times a week. Put out vegetables such as carrots, cucumbers and peas for them to eat. If there are any leftovers in the aquarium within 24 hours, remove them to avoid contamination.

Do fish eat fruit?

Yes. Some species will eat grapes, oranges, guavas, figs and papayas, which have already been studied for consumption in fish diets.

Can you give fish bread?

The short, simple answer is that bread is one of the worst foods you can give most aquarium fish. Bread and any other food prepared for humans must be banned for them.

When should I feed my fish?

According to experts, it is ideal that you feed the fish about twice a day, preferably at times when natural or artificial sunlight is available. There is no ideal time. The only tip is to create a routine to feed the fish at times when you are always at home.

How much does a fish eat per day?

For fry and juveniles, we can assume 4 to 5% of live weight per day. For adult fish, we can estimate 2 to 3% of biomass per day.


Hyslop, E. J. (1980). Stomach contents analysis—a review of methods and their application. Journal of fish biology, 17(4), 411-429.

Malek, A. J., Collie, J. S., & Taylor, D. L. (2016). Trophic structure of a coastal fish community determined with diet and stable isotope analyses. Journal of fish biology, 89(3), 1513-1536.

What do fish eat in the ocean? https://www.legit.ng/1181655-what-fish-eat-ocean.html

Medina, M., Araya, M., & Vega, C. (2004). Alimentación y relaciones tróficas de peces costeros de la zona norte de Chile. Investigaciones marinas, 32(1), 33-47.