Reading a koi food label: protein, fats, ash and additives

Two bags of koi pellets, two very different prices, and numbers on the back that look similar. Should we believe that the difference is just a matter of brand? Not at all. A fish food label is a regulated document, rich in information if you know how to read it. The analytical constituents, the order of the ingredients, and the list of additives reveal a great deal about a food's actual quality, digestibility, and the season for which it is suitable. Here is a method for decoding a bag in just a few minutes, without being impressed by the packaging promises.

What regulations require on a bag

Ornamental fish food sold in the European Union is animal feed for regulatory purposes. Its label must state the type of feed (complete or complementary), the list of raw materials, the analytical constituents, the added additives with their content when required, the directions for use, the batch number, the best-before date, and the net weight.

These statements are sometimes translated approximately or printed in tiny type, but they are there. They are the only verifiable information, unlike the slogans on the front ("explosive growth", "amazing colors"), which commit to very little.

Analytical constituents, line by line

The “analytical constituents” section (sometimes “guaranteed analysis” on imported products) gives percentages measured in the food as sold. Here is how to interpret them.

Crude protein. It includes all nitrogenous substances without indicating where they come from. Fish or krill protein is very well utilized by koi; plant protein (soy, gluten) is utilized somewhat less efficiently, while poorly digestible protein largely ends up in the filter as ammonia. The figure alone is therefore not enough: it must be considered alongside the ingredient list.

Crude fat. Lipids provide energy and essential fatty acids. Sufficient lipid intake allows the fish to burn lipids rather than proteins for its energy needs, reserving proteins for growth and reducing nitrogenous waste. But too much fat oxidizes quickly, becomes rancid, and may promote fatty liver.

Crude cellulose. It measures poorly digestible fiber. Koi, which lack a true stomach, tolerate some fiber, which is useful for digestion, but a high level dilutes nutritional value.

Crude ash. This is what remains after combustion: minerals. Some is essential (calcium, phosphorus, trace elements). A clearly elevated level often indicates fish meals rich in bones or mineral fillers, and above all means fewer useful nutrients per kilo.

Moisture. Not always mentioned, but important for comparison. A dry pellet generally contains less than 10% water. The more water it contains, the less nutritional matter there is per kilo purchased.

The right ranges, as rough guidelines

The values below are not standards, but benchmarks observed in most reputable foods on the market. They provide a quick way to assess a product.

For ash, values around 6 to 12% are commonly found in good-quality foods; above that, look closely at the ingredient list. Cellulose generally remains below 5%.

Comparing two foods on an honest basis

Comparing 36% protein in food with 10% moisture to 36% in food with 6% moisture is like comparing apples and oranges. Nutritionists' method is to convert the values to dry matter.

The calculation is simple: divide the displayed percentage by (100 minus the moisture content), then multiply by 100. Example: food declaring 36% protein and 10% moisture contains 36 / 90 × 100, or 40% protein on a dry-matter basis. Another declaring 36% and 6% moisture contains 36 / 94 × 100, or about 38%. The first is therefore slightly richer than it appears.

The second useful comparison is the protein-to-fat ratio. A quality growth food combines high protein with sufficient fat. A very high-protein food that is low in fat forces the fish to use its proteins as fuel, resulting in more nitrogenous waste for the filter.

The third criterion, more difficult to measure but decisive: digestibility. It depends on the raw materials and the manufacturing process. A practical indicator in the pond is the quantity and appearance of the feces. Well-digested food produces compact, scant feces; mediocre food produces long, bulky strands and water that becomes cloudy more quickly.

The ingredient list: order matters

Raw materials are listed in descending order of weight. The first three or four therefore indicate the food's profile.

• Fish meal, krill, shrimp meal at the top of the list: high-quality animal proteins, highly appreciated by koi.
• Wheat flour, starch: essential binders that help pellets hold together, and a source of energy. When listed first, they indicate a relatively inexpensive food.
• Wheat germ: highly digestible and rich in vitamin E, forming the basis of foods for transitional seasons.
• Soybean meal or flour, gluten: plant proteins, useful as a supplement but less ideal as a main ingredient.
• Yeasts, spirulina, algae: valuable in small quantities, providing vitamins, pigments, and palatability.

Beware of vague categories such as “vegetable by-products” or “cereals” at the top of the list: they allow the manufacturer to vary its raw materials according to market prices, and quality may fluctuate from one batch to another.

Additives: vitamins, pigments, preservatives

Vitamins. Vitamin C is essential for fish, which do not synthesize enough of it. In its simple form, it degrades quickly during production and after opening the bag. Good foods use a stabilized form, often an ascorbyl phosphate. Vitamins A, D3, and E are also included, along with their content.

Pigments. Koi do not produce the carotenoids responsible for their red color themselves: they obtain them from their food. “Color” foods add them in several forms:

• Astaxanthin, the red pigment found in krill and certain microalgae, highly effective on hi.
• Spirulina, a cyanobacterium rich in pigments and protein, often highlighted for color intensity.
• Paprika or marigold extracts, which are more economical and have a variable effect.

Food very rich in pigments, given continuously, can slightly tint white orange in some koi: it is used alternately with maintenance food, and only when the water is warm enough.

Probiotics. Some premium ranges include bacterial strains intended to aid digestion. They may reduce pond fouling, but their effect depends heavily on how the food is stored.

Antioxidants. They protect fats against rancidity. Their presence is rather reassuring, especially in food rich in lipids.

Adjust the ratio to the water temperature

Koi are cold-blooded fish: their digestion slows considerably as the water cools. A food very rich in protein, perfect at 24 °C, becomes a burden at 12 °C. The guidelines below are approximate and should be adjusted according to the fish's behavior.

For the cold period, our article on feeding koi when the temperature drops explains the transition in detail. And for a more general overview of the ranges, see why to choose a maintenance food such as Hikari Staple.

Storing food: quality does not last

Excellent food that is poorly stored becomes mediocre food. Once the bag is opened, air, heat, light, and humidity gradually degrade the vitamins and oxidize the fats.

• Buy suitable quantities: ideally enough for what your fish consume in two or three months.
• Seal tightly after each use, or transfer to a watertight bucket.
• Store in a cool, dry place: never in direct sunlight in an overheated garden shed, and never next to the pump in a damp room.
• Check the smell and appearance: a rancid smell, clumps, whitish dust, or traces of mold indicate that the food should be discarded.
• Observe the best-before date, and note the opening date on the bag.

A detail that is often overlooked: a large 10 kg bag bought for a small group of koi is rarely a good deal. In the final weeks, the food has lost some of its vitamins, and the savings per kilo are lost in quality.

Common case: comparing two labels at the store

Typical situation: food A with 34% protein, 4% fat, 12% ash, wheat flour as the first ingredient; food B with 38% protein, 7% fat, 8% ash, fish meal as the first ingredient, with stabilized vitamin C listed.

Food B is more expensive, but it provides more digestible animal protein, lipid-based energy that spares this protein, and less unnecessary mineral content. Your koi will benefit more from it, and your filter will receive less waste for the same amount fed. Food A may be suitable for an undemanding goldfish pond, but much less so for koi whose growth you are carefully managing.

Read also

From the label to choosing the product: How to choose a good food for my koi carp?.

READ THE ARTICLE

Frequently asked questions

— What protein level should I choose for koi food?

As a guideline, 30 to 38% for a maintenance food, 38 to 45% for a growth food used in warm water, and a less rich, highly digestible food, such as wheat germ, when the water cools.

— What does crude ash mean on the label?

These are the minerals remaining after the food is burned. Some are necessary, but a high level often indicates lower-quality raw materials and dilutes useful nutrients.

— Are astaxanthin and spirulina useful?

Yes, these are sources of pigments that intensify the red color of koi. However, when used continuously and in high doses, they can tint the white; alternate them with a maintenance food.

— How long does an opened bag keep?

Ideally, use it within two to three months, stored in a cool, dry place and sealed tightly. Beyond that, vitamins degrade and fats oxidize.

In summary

• The analytical constituents and ingredient list are the only verifiable information.
• Compare two foods based on dry matter, not on the raw figures.
• High ash content and cereals at the top of the list indicate an economical food.
• Stabilized vitamin C, astaxanthin, and spirulina are good signs, dosed according to the season.
• The protein-to-fat ratio should follow the water temperature.
• Store the food in a cool, dry place, protected from air, and buy reasonable quantities.

Last updated: October 3, 2026.