Biotin (vitamin B7 or vitamin H) is a water-soluble B vitamin that serves as a coenzyme for carboxylase enzymes involved in fat synthesis, amino acid metabolism, and gluconeogenesis (generating glucose from non-carbohydrate sources). In freshwater fish, biotin is particularly important for maintaining healthy skin, scales, and the mucus coat — all of which are critical protective barriers in the aquatic environment.
Biotin deficiency in fish has been well-studied in aquaculture settings and produces a distinctive set of symptoms centered on skin and integument problems. The classic presentation is a blue slime disease — an overproduction of abnormal mucus that gives the skin a bluish, slimy appearance — combined with skin fragility and loss of the normal smooth scale texture.
Like thiamine, biotin can be destroyed by avidin, a protein found in raw egg whites. While this is more of a concern in poultry nutrition (where raw eggs might be fed), it is worth noting for aquarists who occasionally feed raw egg to their fish as a protein source. Cooking denatures avidin and eliminates the risk. Gut bacteria in healthy fish produce some biotin, supplementing dietary intake.
Quality commercial fish food provides adequate biotin. Gut bacteria in healthy fish also contribute to biotin supply. If feeding raw egg as an occasional treat, use the yolk only — raw egg white contains avidin that destroys biotin. A varied diet and healthy gut microbiome are the best biotin insurance.
0.01% of daily nutrient intake
Biotin makes up 0.01% of your freshwater fish's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Blue slime disease (abnormal bluish mucus overproduction on the skin), skin fragility and lesions, loss of appetite, reduced growth, muscle wasting, convulsions, anemia, and in breeding fish, reduced egg hatch rates. The skin changes are the most distinctive and recognizable biotin deficiency sign in fish.
Biotin is water-soluble with an excellent safety margin. No toxicity from dietary biotin has been documented in fish. Excess is harmlessly excreted.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 0.1 | 1 | mg/kg diet | Gut bacteria contribute to biotin supply. Deficiency causes characteristic 'blue slime disease' with abnormal mucus production. Avoid raw egg white which contains avidin (destroys biotin). |
Source: NRC 2011, general aquaculture consensus
