Reading Fish Food Labels
How to interpret a fish food label: crude protein, fat, fibre, ash and moisture in the guaranteed analysis, plus the ingredient list and what fillers and meals mean.
The guaranteed analysis
Fish food labels carry a guaranteed analysis derived from proximate (Weende) analysis, which divides feed into measurable fractions. The main components reported are crude protein, crude fat, crude fibre, ash and moisture. Each is given as a percentage, and together they describe the broad nutritional makeup of the food.
Crude protein
Crude protein is calculated from the total nitrogen in the food, measured by the Kjeldahl method, then multiplied by the factor 6.25 (because protein averages about 16% nitrogen). It is called crude because the method counts all nitrogen, not only nitrogen from true protein. Protein is the most important macronutrient for fish growth.
Protein requirements
- Fry and fingerling diets frequently exceed 50% crude protein (UF/IFAS).
- Grow-out diets often approach or exceed 40% crude protein.
- Maintenance diets may contain as little as 25-35%.
- Carnivores generally need more protein than herbivores.
Fat, fibre, ash and moisture
Crude fat (the ether extract) supplies energy and essential fatty acids. Crude fibre is the plant-derived residue of cellulose, lignin and hemicellulose, which is largely indigestible to most fish. Ash is the total mineral or inorganic content remaining after the sample is burned. Moisture is the water content; dry foods are baked low in moisture to extend shelf life.
Carbohydrate by difference
Carbohydrate is usually not listed directly. In proximate analysis it is reported as nitrogen-free extract (NFE), calculated by subtracting moisture, crude protein, crude fat, crude fibre and ash from 100%. NFE represents mostly digestible carbohydrates such as starches and sugars.
The ingredient list
The ingredient list complements the guaranteed analysis by showing what the food is actually made from. For fish, a high-quality protein source near the top is desirable: fish meal is a major protein source because it provides essential amino acids and long-chain fatty acids (C20 and C22) not found in terrestrial plants or animals.
Whole ingredients, meals and fillers
A meal is a dried, ground concentrate of an ingredient such as fish or shrimp; it is not inferior by definition and often concentrates protein. Fillers are low-nutrition ingredients added for bulk. Crustacean by-products supply carotenoid pigments for coloration, while vitamins such as ascorbic acid (vitamin C) and vitamins A, D, E and the B complex are added to complete the diet.