Understanding Koi & Goldfish Food Ingredients

Koi and Goldfish are ornamental species descended from carp. Though they differ in lifespan, size, and other physical traits, they have similar dietary needs. Their natural food sources in the wild include algae, seeds, insects, and smaller fish. In captivity, pellets packed with similar nutrients are dietary staples. 

How Koi and Goldfish Eat

Koi and Goldfish ingest food through a combination of gulping and suction. Koi have downward-facing mouths and whisker-like barbels, while Goldfish have front-facing mouths and round jaws. Both can chew but can’t bite, making hand-feeding a fun option for enthusiasts. Their gobble-first nature is partially controlled by the buccal cavity, which contains taste buds and mucous-lined goblet cells. The buccal cavity flags and expels non-food items. 

The spectrum of palatable foods is similar for both species (though smaller mouth sizes limit Goldfish). Serrated teeth in the throat grind the hard and crunchy parts of food. These attach to the pharyngeal bones behind the gill chambers and regenerate throughout the lifespan. Food proceeds directly from the esophagus to the intestine, where it is digested, passed to the liver, distributed, and stored in the tissues. 

Commercial Food

Modern fish food pellets are composed of ingredients blended with dough and then extruded under pressure and high heat. The pellets are cut to size, left to dry, and then injected with necessary fats, oils, and preservatives. These ingredients prevent spoilage and make the food easier to digest. 

Most pond Goldfish and Koi foods are labeled as suitable for both types of fish. Koi require more protein than Goldfish, so it is better to choose a Koi formula if you have a mixed pond. Don’t use food created for other fish species. A diet with the wrong nutrient profile can hinder growth and lead to stress or illness. 

Floating vs. Sinking Pellets 

When buying commercial fish feed, you can choose between floating or sinking pellets. Floating pellets are lighter, less dense, and manufactured at lower pressures. As a result, they will hover at the pond’s surface until saturated, allowing Koi and Goldfish to dine in plain view. Sinking pellets are heavier and denser and are formed under high pressure. They immediately drop to the pond’s floor, where the fish’s natural bottom-feeding habits can activate. 

Floating 

Floating pellets are the more popular choice among ornamental pond owners. First, they allow food intake monitoring. Overfeeding is one of the common mistakes pond owners make, and it generates many problems for your fish and the water quality in your pond. Floating pellets allow you to monitor portions more easily. You can set a timer (we suggest five minutes) for feeding and remove leftovers with a skimmer. 

Next, floating feed enables you to visually inspect fish and spot problems early. Lesions, discoloration, missing scales, tattered or clamped fins, or bloating can indicate bacterial or parasitic infections. These often accompany changes in behavior, such as abnormal swimming patterns, lethargy, or aggression. Forcing your fish to come to the surface to feed provides you with a daily opportunity to inspect their appearance.

Finally, this feeding method offers an excellent opportunity to interact closely with your Koi and Goldfish. Eventually, your fish will recognize you and eagerly approach you for a meal or treat. You can even use mealtime to teach your Koi or Goldfish a few tricks. In addition, your backyard can offer a social opportunity for humans–fish feeding can be a fun activity for the whole family, as well as guests. 

Sinking

Sinking pellets are a more natural feeding method for Koi. Expert hobbyists sometimes prefer them because they enable Koi and Goldfish to grow faster, which is a plus if you want to show or sell them. They also provide higher feeding efficiency, as measured by the increased growth rate-to-food volume ratio. Some studies suggest sinking food can improve efficiency over floating pellets by up to 20%. 

We recommend using sinking pellets in ponds or tanks with Fancy Goldfish. These varieties have more compact body structures than pond Goldfish and Koi. This puts more pressure on their internal organs, which the air consumed during surface feeding exacerbates. Air ingestion can inflate the swim bladder, causing hyperbuoyancy and rendering the fish incapable of swimming below the surface. Pond Goldfish have a more streamlined digestive system and can handle a small amount of air with floating pellets without issues.

Mixed 

Some people opt for a mixed feeding method to cater to a diverse population. Using floating and sinking pellets is suitable in ponds with new fish or ones that differ significantly in size. Most newly introduced Koi and Goldfish shy away from the school while they adjust to their environment, hiding under rocks or plants, where sinking pellets will meet them. Similarly, large and eager Koi might intimidate your smaller Goldfish during mealtime. However, mixing floating and sinking pellets is suitable only for experienced pond owners. 

Flakes

If you’ve been to a pet store, you know fish flakes are incredibly common. They exist for almost every type of fish you can keep, including Koi and Goldfish. While flakes are popular among Fancy Goldfish owners, pellets are a better option. Despite similar nutritional content, flakes induce the most air ingestion. If using flakes, hold them underwater for a few seconds before releasing them to minimize floating.

Healthy Treats

Incorporating fruits and vegetables into your Koi and Goldfish’s diet can help reduce stress levels, enhance their immune systems, and promote growth and color development. Fruits and vegetables are rich in fiber, vitamins, and antioxidants, which contribute to overall health when consumed in moderation. Opt for fruits and vegetables that are lower in sugar and carbohydrates, such as berries and green, leafy vegetables. Reserve high-carb options, like citrus fruits and root vegetables, for special occasions.

As omnivorous species, Koi and Goldfish relish a meaty treat. Some excellent options include bloodworms, brine shrimp, and clams, all of which are suitable for supplemental feeding. These foods are rich in proteins, oils, vitamins, and minerals, helping to strengthen Koi’s natural defenses against illnesses and support digestion. Most of these options are available freeze-dried as an alternative to live food. 

For high-protein vegetarian options, you can feed your Koi and Goldfish eggs and cheese. Boil the eggs and cut them into small pieces. Select high-quality cheeses that contain minimal artificial ingredients and preservatives. Offer these snacks only when the water temperature is 65°F or higher. 

Nutrition 

All food types will have three consistent staples: protein, fat, and carbohydrates. The advisable ratio depends on the season. During the summer, Koi and Goldfish eat most frequently (up to four times a day) and need the highest protein formula compared to other seasons. In the fall and spring, a lower-protein, higher-carb diet is sufficient, offered once or twice daily, depending on the temperature. Do not feed outdoor fish when the water temperature drops below 50°F. 

Protein

The most important element of Koi and Goldfish diets is protein. Proteins are essential for growth, tissue repair, and strength. Koi, especially young Koi, require high levels of protein. Ideally, 35% or more of their diet should be protein. Protein sources include animal-based proteins, such as fish or porcine meal, and vegetable-based proteins, such as wheat or soybean meal. 

Lipids

Lipids, or fats and oils, are the best energy source for Koi. They help in the absorption of fat-soluble vitamins and are essential for certain metabolic functions. Lipids can come from fish meal, wheat germ, and other unsaturated fatty acids like omega-3 fatty acids. Ideally, Koi food should be 3-10% fat. Younger fish need more fat, but fat content can be reduced as Koi mature. Deficiency in these essential fatty acids can slow growth, cause fin erosion, and contribute to color loss. However, excessive fat intake can lead to weight gain and liver issues, so it’s essential to monitor fat consumption closely. 

Carbohydrates

While Koi should get most of their energy from protein, lipids, and other amino acids, carbohydrates help provide quick energy to aid in digestion. Research has also found that Koi diets lacking carbohydrates produce less growth than those with carbohydrates. However, too many carbohydrates can cause Koi and Goldfish to gain weight too quickly, so it’s best to limit carbohydrates to no more than 40% of a Koi’s diet. Some sources of carbohydrates include wheat, soybeans, as well as fruits and vegetables.  

Vitamins

Vitamins are essential for maintaining Koi and Goldfish health. They are necessary for most metabolic reactions, and a lack of vitamins can lead to poor growth, loss of color, and a weakened immune system. The most important vitamins for Koi and Goldfish are B, C, A, D, and K. Below is a list of vitamins you may see in the ingredients of fish feed and the purpose of each. 

Ingredient	Vitamin	Purpose
Biotin	B7	Breaks down food into energy Helps with metabolic function Helps keep eyes, liver, skin, and nervous system healthy
Calcium Pantothenate	B5	Helps break down and convert fats, proteins, and carbohydrates into energy
Choline Chloride	B4	Helps improve nervous system function and aids in metabolic processes and breaking down fats
Folic Acid	B9	Helps improve growth and health by synthesizing and repairing DNA
L-ascorbyl-2 polyphosphate	C	Boosts the immune system
Menadione Sodium Bisulfite Complex	K	Helps with blood clotting and building strong bones
Nicotinic Acid	B3	Helps break down complex molecules and convert nutrients into energy
Pyridoxine hydrochloride	B6	Helps convert nutrients into energy Helps with nerve function
Riboflavin	B2	Promotes growth Helps regulate physiological functions
Thiamine Mononitrate	Salt form of B1	Fortifies Koi food to help with metabolization
Vitamin A acetate	A	Helps with the proper growth and development of bones, skin, and scales
Vitamin B-12 supplement	B-12	Helps with red blood cell production and proper function of the nervous system
Vitamin D3 supplement	D3	Aids in proper bone formation
Vitamin E supplement	E	Helps maintain proper metabolic function and normal growth

Minerals

Minerals are vital for growth and development. A deficiency in minerals can cause weak bones or abnormal bone growth and can lead to certain diseases. While water provides several of the trace minerals Koi and Goldfish need, some essential minerals must be introduced through food. Below is a list of essential minerals for Koi that need to be introduced through food, how they may appear in the ingredient list of fish food, and the purpose of each. 

Mineral	Name in Ingredient List	Purpose
Calcium	Calcium carbonate,  Calcium iodate	Helps build strong bones Improves cardiovascular health
Magnesium	Manganous oxide	Helps bone growth Strengthens metabolic function and cell membranes
Iron	Ferrous carbonate	Helps provide oxygen to the blood
Zinc	Zinc oxide, Zinc sulfate	Helps protect from free radicals Aids in tissue regeneration Helps immune function and nutrient absorption  Helps improve cellular function and repair
Copper	Copper sulfate	Helps in the production of blood cells and connective tissues Aids in the proper functioning of the nervous system

Carotenoids 

Carotenoids are naturally occurring pigments that, when consumed, impact the pigmentation of Koi and Goldfish. While they aren’t considered essential to the health of your fish, they do help enhance the colors of a Koi and Goldfish’s bodies. The most common ingredients containing carotenoids found in fish feed are marigold extract, spirulina, and canthaxanthin.

How to Feed

Water temperature is one of the most critical factors influencing feeding. Koi and Goldfish metabolisms speed up in warmer water and slow down in cooler water. To accommodate this, you must adjust the type of food you give your fish when seasons change.

Koi and Goldfish can be fed a regular, all-season formula when temperatures are above 65°F. When water temperatures are below 65°F but above 50°F, you’ll need to switch to an easily digestible food. Wheat germ-based formulas are the most popular choice. Stop feedings completely when water temperatures drop below 50°F.

Water temperature also determines the frequency of feedings. When temperatures are consistently above 70°F, Koi and Goldfish should be fed three to four times per day. One to two times daily is appropriate for temperatures between 62°F and 70°F, and once a day or once every other day for temperatures between 50°F and 62°F.