Vitamin B12 (cobalamin) is a cobalt-containing vitamin essential for red blood cell production, nervous system function, and DNA synthesis in freshwater fish. It works closely with folate in the production of red blood cells and in the methylation reactions that are fundamental to cell division and gene regulation.
Freshwater fish obtain B12 primarily from animal-based food sources — in the wild, this comes from the bacteria in zooplankton, insect larvae, worms, and other small invertebrates. Fish meal and crustacean-based ingredients in commercial food are excellent B12 sources. Some B12 is also produced by bacteria in the fish's own gut and in the biofilm that coats aquarium surfaces, though the contribution from these sources is uncertain.
For herbivorous species like plecos and otocinclus, B12 availability is worth considering since plant foods contain essentially no B12. These fish likely obtain some B12 from the bacterial component of the biofilm and aufwuchs (the biological film on surfaces) that they constantly graze on — a natural feeding behavior that serves both fiber and micronutrient needs. This is one reason why algae wafers and blanched vegetables alone may not provide complete nutrition for herbivorous fish without some animal-based food component.
Provided by any quality commercial fish food containing fish meal or crustacean ingredients. For herbivorous fish like plecos and otocinclus, ensure they receive some animal-based food (algae wafers often contain shrimp meal) in addition to vegetable matter. A mature aquarium with healthy biofilm on surfaces also provides natural B12 through bacterial activity.
0.0% of daily nutrient intake
Vitamin B12 (Cobalamin) makes up 0.0% of your freshwater fish's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Anemia (pale gills, reduced stamina, gasping), poor growth, dark discoloration of the skin, lethargy, reduced appetite, neurological symptoms including poor coordination and abnormal swimming patterns, and in breeding fish, poor egg quality and fry survival.
B12 is water-soluble and excess is excreted. No toxicity from dietary B12 has been reported in fish. It has an extremely wide safety margin.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 0.01 | 0.05 | mg/kg diet | Required in very small amounts. Animal-based food ingredients and gut bacteria provide adequate B12 for most fish. Herbivorous species may need supplemental sources. |
Source: NRC 2011, general aquaculture consensus
