An example of assay for vitamin deficiency calculation is now given from George Post's book. "Rainbow trout in a raceway have developed macrocytic anemia, fragile caudal fins, are darker in color are reduced in growth and lethargic. Folic acid deficienvcy is suspected,

"There are 1.000 fish in the raceway. The average age size as determined by weighing a representative sample and counting the nimber, is 540 fish per kg and water temperature is 16 C. The feeding level is 5.3 % of the total fish weight per day. Folic acid was 2.2 mg per kg of ration.

"Determination of adequacy of the dietary folic acid as follows.
Minimum daily folic acid requirement--0.15 mg/kg of fish per day
Minimum folic acid for 1.000 kg fish--150 mg per day
Feeding level 5.3 % body weight--53 kg ration per day
Ration assay folic acid results--2.2 mg per kg of ration
Therefore 53 kg ration must contain 150 mg folic acid
But 53 kg ration X 2.2 mg folic acid = 116.6 mg actual folic acid in 53 kg ration
Diagnosis: Folic acid is supplied below the minimum and could cause the disease signs."
See also National Research Council. 1993. Nutrient requirements of fish. National Academy Press, Washington, DC, 114 p.