Fish Food Basics

What to feed your freshwater fish.

Fire Goby (Nemateleotris magnifica). Via FromSandToGlass/Flickr

Our fish rely on us completely for their nutrition and overall health. The food we provide can manipulate how fast they grow, when they reproduce, how colorful they are and how strong their immune system stays. A wide variety of high-quality fish foods can help us accomplish this. To provide proper nutrition, you must understand the needs of your fish and the foods available within the hobby.

Coolwater Versus Tropical Fish

Freshwater fish can generally be divided into two groups: coolwater and tropical. The coolwater fish have lower metabolic rates, so they require less protein in their diet. This is because fish cannot regulate their body temperatures, so nutritional requirements are driven by the temperature of the surrounding water. The higher the water temperature, the more frequently fish need to be fed and the total volume of food consumed will be greater.

Coolwater fish kept in the home aquarium are usually goldfish and koi. Kept inside at a constant temperature, a diet around 33-percent protein supplemented with zucchini slices is ideal. Kept outdoors at variable temperatures requires seasonal diets with protein content increasing slightly during the hottest months of the year. There are many good koi diets available that offer ingredients that are ideal for spring, summer and fall. Outdoor ponds generate food in the form of algae, insects, etc., so don’t overfeed with commercial foods.

Tropical fish may be divided into four types of feeding groups: limnivores, herbivores, omnivores and carnivores. Limnivores graze on algae and the microorganisms that live on algae, small worms, etc. Herbivores are plant-eaters and algae-grazers. Limnivores and herbivores often have specialized teeth and mouths for scraping algae off plants, rocks, etc.

The common bristlenose catfish is a member of the Ancistrus genus and requires wood in its diet. Foods are available with added wood like willow bark, but the common solution is to provide driftwood in the tank.

I have a few Ancistrus in my 75-gallon show tank. I put a cave made out of half a coconut shell in the tank, and the Ancistrus have completely eaten the fibrous outer layer of the shell. Herbivores have longer intestines than carnivores to completely break down plant material. They expend less energy in gathering food so require less protein.

Omnivores eat both plants and animals. Omnivores require a little more protein, so 40 percent is a good target. Check the percentage on the food ingredient label. Carnivores are predators that eat insects and other fish. Carnivores that eat mostly insects are focused on the water surface and contain some of the more fascinating fish like the archerfish (Toxotes jaculatrix), which shoots a jet of water to knock insects out of the air into the water. Carnivores require the most protein, so 40 to 48 percent is a good range.

Archer fish
Archer fish (Toxotes jaculatrix). Photo by Al Castro/I-5 Studio

Keep in mind that young fish that are growing rapidly require small amounts of food frequently and more minerals, vitamins and protein than mature fish. For carnivorous fish, it is common to feed 48 percent protein food for juvenile fish and 40 to 43 percent protein for adult fish.

The four groups are then divided further based on surface-feeders, midwater feeders and bottom-feeders. Consideration must be given to size of the mouth and throat. Teeth also play a role, with some fish having jaw teeth (e.g., characins) and others pharyngeal teeth (e.g., barbs).
Characins bite their food and swallow the pieces whole, so avoid any foods that swell. Characins are among the most popular fish in the hobby and include the neon tetra.

The Cyprinids (e.g., barbs, carps and minnows) have jaws with no teeth and no stomach. They grind or crush their food with teeth located at the pharyngeal arch of the throat. The clown loach is one of the most popular of these Cyprinids with pharyngeal teeth.

Cichlids have both jaw and pharyngeal teeth so they bite off large pieces, chew and crush them. African cichlids are very popular in the hobby and include many types of specialty feeders. A popular group is Tropheus from Lake Tanganyika. These fish graze on algae and should not be given too much protein, so supplement with zucchini rather than freeze-dried foods.

Investigate Fish Food Ingredients

The foods readily available to the hobbyist are flake, pellet, freeze-dried, frozen and live food. Read the list of ingredients. The first few ingredients should be high-quality items like whole krill meal, whole sardine meal, herring meal, kelp, Spirulina, whole salmon, halibut, etc. Lower-grade foods list fish meal, dried yeast and ground brown rice in the first few ingredients.

Other quality ingredients to look for are astaxanthin, Spirulina and calcium montmorillonite clay. Herring and salmon provide Omegas 3 and 6, highly unsaturated fatty acids (HUFAs), which are essential for the immune system. All fish foods contain preservatives like ethoxyquin, tocopherol and stabilized vitamin C, either added by the manufacturer or in the various meals used as ingredients.

Protein levels are important. Good protein percentage targets are: 30 to 35 percent for goldfish and koi; 35 to 40 percent for omnivores; and 40 to 48 percent for carnivores. The source of protein, though, is more important, so check the first four ingredients. Excessive amounts of protein are not healthy, particularly for herbivores. Wheat flour acts as a binder and is necessary, but it should come after the first three ingredients. Soybean is used in some foods as a source of protein. This does not contain the complete amino acid profile necessary for the fish. Avoid foods with a lot of fillers and dyes for color. Avoid packaging that allows light to degrade the food. Resealable, opaque packages that do not allow light inside are best.

Various fish foods
Various fish foods. Photo by Gina Cioli/I-5 Studio

Fish Food Breakdown

Flakes: This is by far the most common type of fish food and is manufactured with a wide range of ingredients. Flake foods are ideal for community tanks. They float so surface-feeders with small mouths have easy access, then the flakes slowly float down to midwater feeders and finally sit on the bottom. Look for a protein level of around 40 percent (unless you have all goldfish; then 33 percent is fine), with kelp or Spirulina in the first three ingredients listed on the label.


This food is generally classified as floating or sinking pellets. I prefer a very small pellet that floats for a while and then slowly sinks to the bottom. Compressed pellets made from flakes are usually nutritionally equivalent to flakes, so if you want a pellet, choose an extruded pellet. This information often is not on the label, so research online or ask your local fish expert to find out for you. Extruded pellets are cooked at lower temperatures so the amino acids and vitamins hold up better than flakes in the manufacturing process. Flakes are cooked at much higher temperatures to drive out enough moisture so they can be flaked.


This food is very convenient to use. Bloodworms, Tubifex, brine shrimp, Mysis, etc., are readily available in this form.


A wide variety of frozen foods are now available. Be sure to rinse thoroughly before feeding to your fish. This reduces pollution and phosphates. Nutrition can be increased by soaking for a few minutes in vitamins.
Gelatin: These are dry mixes that are combined with hot water. I pour the mixture into ice cube trays and store in the refrigerator. Each cube will last in the aquarium for a few days, which provides a constant supply of food to young fish.
Homemade: You can make your own foods by using a small food processor and freezing the mixture. Be sure not to add anything with saturated fats. Fish can’t process saturated fats, so these end up stored as fatty deposits around the liver. This includes beef heart. I know you can find lots of people recommending beef heart, but fish were not designed to eat cow with saturated fats. The fatty deposits created by feeding your fish beef heart is unhealthy. Remember, just because the fish like to eat it doesn’t make it good for the fish, so do your research.

Live Foods:

I raise litter worms (red wigglers), scuds and microworms because, for me, they seem to be the easiest live foods to raise, but many others are available online. “Culturing Live Foods: A Step-by-Step Guide for Culturing One’s Own Food for the Home Aquarium” by Michael R. Hellweg is an excellent book on the subject. A good online resource for live food cultures is Also, go to your local aquarium club meeting. You will find help with anything you want to accomplish as a hobbyist.

More Fish Feeding Tips

Once you get the main diet of your fish settled, you can think about additional items.


Vitamins are available in liquid form and can be added to many types of foods. Instructions usually say to add them to the water, but I find it most effective to soak food in them for a few minutes prior to feeding.


If you want to feed for color, offer foods high in sources of beta carotenes like krill, shrimp, salmon and astaxanthin (Haematococcus algae). Carotenoids enhance the colors of red and orange. Spirulina is a blue-green algae and is used to enhance the color blue. Feed hard-boiled, dried egg yolk in small quantities to enhance yellow. Some commercial diets use testosterone to enhance color, but this is not practical for ornamental fish because of all the negative side effects, which include premature maturity and sterility.


If you wish to feed for breeding, L-lysine and L-ornithine are amino acids that stimulate spawning. These are found in animal proteins, and live foods are the best sources if you are serious about breeding your fish. Larger than normal water changes and supplemental feeding with live foods is often all it takes to encourage healthy, mature fish to breed.

Knowledge Fuels Enthusiasm

Offer a wide variety of foods with your fishes’ feeding habits and nutritional needs in mind. It may sound like homework, but I’ve found the more you know about the fish you keep, the more enjoyable your hobby. Over the years, I have met many hobbyists who specialize in one area or another, and they know an incredible amount about their area of expertise. In every case they acquired the knowledge to become successful and that success is what fuels their enthusiasm for the hobby.

There is such a wide diversity of food available to the hobbyist now that you can keep almost any fish healthy. Remember to feed small amounts on a regular schedule and good luck!

Scott Craig has kept and bred tropical fish for more than 50 years and has worked with or for many of the manufacturers in the industry.

Article Categories:
Fish · Health and Care