Riboflavin (vitamin B2) is a water-soluble vitamin that serves as a building block for two critical coenzymes — FAD and FMN — that drive dozens of metabolic reactions in a fish's body. These coenzymes are essential for converting food into cellular energy, metabolizing fats, and maintaining healthy skin, eyes, and nervous tissue.
Riboflavin is particularly important for eye health in fish. Deficiency is strongly associated with cataracts (lens opacity) in several fish species — a finding that has been well-documented in aquaculture research. Cloudy eyes in aquarium fish are often attributed to water quality problems or bacterial infections, but chronic riboflavin deficiency can be an underlying cause that gets overlooked.
In practical terms, riboflavin deficiency is uncommon in aquarium fish fed a varied diet of quality commercial foods, because fish meal and other animal-based ingredients are naturally rich in B2. The risk increases for fish kept on a monotonous diet of a single food type, particularly if that food has been stored improperly or for too long, as riboflavin is sensitive to light degradation.
Provided by quality commercial fish food. Store food in a dark, cool location since riboflavin is degraded by light — clear containers on a brightly lit shelf will lose riboflavin faster. A varied diet including frozen bloodworms, brine shrimp, and spirulina-based foods ensures adequate B2 intake.
0.1% of daily nutrient intake
Vitamin B2 (Riboflavin) makes up 0.1% of your freshwater fish's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Cataracts (cloudy lens visible as a white or gray opacity in one or both eyes), poor growth, loss of appetite, anemia (pale gills), hemorrhaging at fin bases, light sensitivity, dark skin discoloration, and general lethargy. Cataracts from riboflavin deficiency may be reversible if caught early and dietary riboflavin is restored.
Riboflavin is water-soluble and excess is excreted readily. No toxicity from dietary riboflavin has been documented in fish. It is one of the safest B vitamins to supply in abundance.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 3 | 10 | mg/kg diet | Light-sensitive — store fish food in dark containers. Deficiency linked to cataracts in multiple fish species. |
Source: NRC 2011, general aquaculture consensus
