What Do Pond Fish Eat? (Natural & Supplemental Foods)

Most common pond fish are omnivorous, and will eat quite an – perhaps unexpected – array of foods if provided. For example, koi and goldfish will eagerly consume peas, citrus fruits, squash, spinach, wheat germ, plankton, blood worms, shrimp, and even algae!

However, a fish’s diet does depend at least somewhat on water temperature. In warmer waters (above approximately 60 degrees Fahrenheit), fish metabolism is high and they will need protein-rich foods. In waters below 60 degrees, a diet lower in protein and higher in carbohydrates can also be suitable, such as with fruits and veggies, is more suitable as their metabolisms are significantly lower and they won’t need as much energy as in warmer months.

Here we will discuss the basic dietary requirements of some of the most commonly kept pond fish species – goldfish, koi, and sturgeon – as well as recommend some healthy food choices you can feed your pond fish besides normal pelleted foods.

What Will Pond Fish Eat Naturally?

In a fully natural environment without supplemental food, familiar pond fish species still have a diverse diet and are adept at finding sources of food. Goldfish in particular are known to be opportunistic eaters, and will eat plants such as water sprite and duckweed, crustaceans, insects and aquatic macroinvertebrates (such as caddisfly, mayfly, and mosquito larvae), and tadpoles.

Larger goldfish may also eat fish smaller than themselves, as well as frogs. Wild koi (also known as the common carp, the domesticated koi carp’s ancestor) will readily eat aquatic insects, flies, algae, smaller fish, plants like water lily and water lettuce, snails, and frogs. As bottom feeders, they also browse along the water body’s floor using their maxillary barbels for any live or decaying plant or animal matter that has settled amongst the substrate.

Sturgeons in the wild can grow to be massive (around 100 pounds, and over 500 pounds in the case of the Atlantic sturgeon), and it takes a great deal of food to achieve and sustain such a hefty size. Like koi, they are bottom dwellers and rely on sensitive facial barbels to locate everything from clams and barnacles to snails, fish eggs, insect larvae, shrimp, dead fish, and even sizeable fish such as salmon and flounder.

What Can You Feed Koi & Goldfish Besides Pellets? 

1) Supplemental Proteins 

Quick answer: Brine shrimp, soybean meal, insects, bloodworms, silkworms.

For added nutrition, your pond fish can be fed a multitude of other supplementary foods. Nearly all fish require 10 amino acids (the building blocks of protein), and these can be supplied through protein sources like brine shrimp, bloodworms, silkworms, soybean meal, and naturally occurring insects and worms.

Goldfish and koi are able to digest both plant-based proteins and animal-based proteins, but shrimp, bloodworms and the like should be provided in small quantities and are usually considered “treats.” Sturgeon require around 40% of their diet to be composed of protein (obtained mostly from animal sources, contrary to koi and goldfish), and 30% and 35-40% for goldfish and koi, respectively. Younger fish require more protein since they are growing, so supply an additional 5% protein for them.

2) Supplemental Carbs & Sugars

Quick answer: Raspberries, shelled peas, carrots, watermelon, broccoli, cheerios, lettuce and citrus fruits.

Fish also need carbohydrates to supply prompt energy, though not usually in great supply – koi and goldfish are prone to suffer from liver degeneration, often unbeknownst to the pond keeper, as a result of being fed too many carbohydrates. To be on the safe side, keep their diet composed of at or below 10% carbohydrates.

Raspberries, wheat germ, shelled peas, watermelon, broccoli greens, citrus fruits, and cheerios (in small amounts, as cereal grains are very starchy for fish) will provide not only carbohydrates, but other necessary vitamins and fiber as well. Carrots and shelled peas (either boiled lightly or ground up) can also help enhance the color of your fish, as can spinach and spirulina (a species of blue-green algae).

3) Supplemental Fats (Lipids)

Quick answer: Brine shrimp, bloodworms, silkworms, krill, fish oils, soy bean meal.

Lipids, or fats, are the main fuel source for energy metabolism in fish muscles, providing as much as twice the amount of energy as protein or carbohydrates, and contain vital fatty acids. Fish with lipid-deficient diets have been found to experience stunted growth, deformities, and other issues.

Linseed oil is one of the best types of oil for fish, as it provides an adequate amount of both linolenic and linoleic acids, the two essential fatty acids needed by many common pond species (particularly koi). Aquatic oils (derived from salmon, krill, shrimp etc.) are also an acceptable choice for pond fish. Essential fatty acids should compose around 5-10% of goldfish and koi diets and 10-15% for sturgeon.

Be aware that organisms (terrestrial and aquatic alike!) can develop potentially deadly diseases if they eat too much fat. For example, South Africa and Mozambique’s Nile crocodile populations began to plummet suddenly beginning in 2008 due largely to a fatal disease called pansteatitis that is most closely linked to high polyunsaturated fat intake and low vitamin E levels (among other factors, including poor water quality). This disease has also been found to present itself in fish, turtles, birds, and even domestic dogs and cats for the same reasons.

With this in mind, moderate the fat intake of your pond fish and supplement with a bit of vitamin E to ensure proper cellular metabolism of fats and any toxins that may be present in the environment. Healthy fats, including linoleic acids and vitamin E, can be found in high quality pellet feeds, or in supplemental foods such as brine shrimp, bloodworms, silkworms, krill, or soy bean meal. You can also try making your own fish food so that you know exactly what is going into their food and how much.

Most fish require only small amounts of vitamins and minerals, which can be obtained easily via the food sources already listed (fruits, veggies, carbohydrates, and so on), as well as directly from the water itself via osmotic diffusion. However, iron, zinc, copper, and magnesium cannot be obtained from the water by fish and have to be acquired from their diet, though these are needed in fairly minute amounts and so you likely won’t need to concern yourself with supplying them directly.

The Benefits of Feeding Pellet Foods (Why You Still Should)

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To be certain that your fish are meeting all of their dietary needs, it is best to use a high quality pellet feed, though you can provide supplemental feedings now and again of the things listed above, in moderation. Pellet feeds often contain high protein content as well as all of the essential vitamins and minerals that your fish need, so this makes it easy and straightforward to keep track of the exact nutrient types and amounts that your fish are getting.

Utilizing pellet feeds helps ensure that your fish will have a well-rounded diet, and in turn will promote healthy growth, decrease the likelihood of disease, and aid in building a strong immune system. Some even have added enhancers to improve color, though it has been argued by some that fish color is more so tied to water quality and genetics than diet.

Regardless, do your research on pellet feeds to make sure that you choose one(s) that meets your specific fish requirements. Also, you may wish to opt for floating pellets as these will help you to monitor how much your fish are eating, and can be easily removed if the pellets are not entirely consumed.

Sinking pellets that don’t get eaten will add excess nutrients to your water and can adversely impact water quality, fueling algae growth and depleting much-needed dissolved oxygen in the water. As a general rule, only feed your fish what they can eat in 5 to 10 minutes – don’t be fooled by their continued begging, as you’ll risk overfeeding them and sullying the water quality.

If you have koi, you can also check out our guide to nutrient balanced koi food recipes here!