Fish Calories Calculator

How the estimate works

No lab has published a calorie requirement for every aquarium species. This tool does not pretend otherwise. It uses four clear steps instead.

1. Start with a feeding rate. Each species has a typical adult range. It is written as a percent of body weight per day in dry food. These are general aquarist guidelines and not measured requirements.
2. Adjust for life stage and goal. Juveniles get 1.8 times the adult rate. Seniors get 0.8 times. Growth support adds 25 percent. Slimming down takes off 30 percent.
3. Adjust for temperature. Fish are cold-blooded, so appetite and metabolism follow the water. The tool doubles or halves the amount for about every 10°C (18°F) away from the species' ideal. It limits the change to a safe band.
4. Convert to calories or grams. The dry-food amount is multiplied by about 3.6 kcal per gram, a typical figure for as-fed flakes and pellets. Other foods are converted by their own energy density.

A worked example

Take one 80 g goldfish in 68°F water. Goldfish eat 1 to 2 percent of body weight in dry food each day. That is 0.8 to 1.6 g. Multiply by 3.6 kcal per gram and you get about 2.9 to 5.8 kcal per day. Split that into two meals and each meal holds 0.4 to 0.8 g of food.

Now take a 1,000 g koi at 68°F. Koi eat 0.5 to 1.5 percent. That is 5 to 15 g of dry food, or 18 to 54 kcal per day. Small fish eat a bigger share of their weight than large fish, so a 2.5 g betta needs 2.5 to 4 percent. That is only 0.06 to 0.10 g, or about 0.2 to 0.4 kcal.

Typical feeding rates by species

These are the starting rates behind the tool. They assume an adult fish, dry food and the ideal water temperature.

Species feeding notes

Goldfish

Omnivore. Goldfish have no true stomach and make a lot of waste, so small meals matter. Soaked pellets or sinking food cut down on air gulping.

Betta

Carnivore. Bettas have tiny stomachs. Pellets swell once wet, so soak them or offer only a few at a time.

Guppy

Omnivore. Guppies nibble all day and handle small, frequent meals well. Fry need several tiny feedings daily.

Angelfish

Omnivore (leans predatory). Angelfish take flakes and pellets but do best with some frozen foods mixed in.

Neon tetra

Omnivore. Small mouths, schooling habits. Use micro pellets or crushed flake.

Koi

Omnivore. Koi appetite follows pond temperature. Feeding usually stops near 50°F, and cool-weather food is easier to digest.

Cichlid (African mbuna type)

Mixed (varies by species). This entry is a baseline for mbuna-type cichlids. Some cichlids are herbivores and some are predators, so check your exact species.

Pleco (bristlenose)

Mostly plant matter. Plecos graze algae and wood. They need sinking food with vegetable content, and wafers alone are not a full diet.

Gourami

Omnivore. Gouramis eat at the surface, so floating food suits them.

How water temperature changes the result

Fish do not heat their own bodies. Their metabolism follows the water. Biological rates often double for every 10°C (18°F) of warming inside a species' comfortable range. The tool compares your water temperature with the ideal for the species and applies a factor.

The cap is on purpose. Warm water holds less oxygen, and a fish at the hot edge of its range does not need a feast. A goldfish at 60°F needs about 25 percent less than at 68°F. A betta at 72°F needs about a quarter less than at 79°F. Koi below about 50°F should not be fed at all.

If the water is too hot or too cold for the species, fix the water first. Stressed fish digest poorly, and their uneaten food then spoils the tank. Check the heater, and read a thermometer before you read a feeding chart.

Life stage and goal

Young fish grow fast and need more food for their size. Older fish slow down. The tool applies these multipliers on top of the species rate.

Calories in fish food

A calorie figure on fish food is an estimate of energy per gram as fed. Dry flakes and pellets sit near 3.4 to 3.8 kcal per gram. Frozen foods sit near 0.4 to 0.6 because they are mostly water. So 6 g of frozen bloodworms match the energy in 1 g of flake.

Gross energy is what a food contains. Usable energy is what the fish digests, and it is lower. Makers rarely publish digestible energy for aquarium foods. That is why this tool uses category figures and calls them estimates. Compare foods on a dry-matter basis and check the nutrition table before you switch.

Fish also need far fewer calories per gram of body weight than a land animal of the same size. They do not burn energy to stay warm, and water supports their weight. That is why fish portions look so small.

What to do with your result

• Weigh the food. A jewelry scale that reads to 0.01 g costs little and ends the guessing.
• Split the amount. Most adults do well on one or two meals. Small fast fish do better on three.
• Use the two-minute check. Offer only what your fish finish in about two minutes. Net out the rest.
• Check body shape. A firm, slightly rounded belly is normal. A sunken belly means add a little. Cloudy water and stringy waste mean cut back.
• Wait two weeks. Hold the new amount before you judge it. Then change by small steps.

What the tool cannot know

It cannot see your fish's body condition, tank mates, algae grazing or the real digestibility of your food. Treat every result as a starting point. Feed it for two weeks and watch. Round bellies and leftover food mean you should cut back. Thin bodies and constant searching mean you should add a little. For deeper background, read the National Research Council book Nutrient Requirements of Fish and Shrimp (2011). It covers farmed species, which is the best research base available.