The standardization of diets for laboratory rodents in the 1970s minimized the contribution of unintended nutritional effects to experimental outcomes and made comparison between experiments more reliable (Nature 491, 31–33; 2012). Despite success as a model species, zebrafish (Danio rerio) are still fed assorted commercially available diets of largely unknown nutrient composition. It is time to develop a standard formula diet for zebrafish in the laboratory, applying the extensive knowledge of fish nutrition from aquaculture.

We analysed the iron content of four commercial zebrafish diets and found that they contained 0.6–4.6 grams of iron per kilogram (g kg−1) of dry feed. Because fish have a maximum iron requirement of 0.2 g kg−1 dry feed, these higher concentrations could be toxic. In salmon, for example, differences in dietary iron affect the cytochrome P450 detoxification system (A. Goksøyr et al. Can. J. Fish. Aquat. Sci. 51, 315–320; 1994). One zebrafish diet was also deficient in vitamin C — a combination that would alter cellular redox status and could influence study parameters such as disease progression.

Failure to control for such variables compromises the validity of outcomes from zebrafish receiving different nutrition in an otherwise identical experiment.