How to calculate commercial fish feeding requirements

To calculate how much food to feed a tank containing fish being grown out as food fish (that is not ornamental fish) in a recirculating aquaculture system use the following as a rough guide:

• Fish from weaned to 30 days old feed at the rate of 10 - 15 % of their average body weight per day
• Fish from 30 days to 60 days old feed at the rate of 5 - 10 % of their average body weight per day
• Fish from 60 to 90 days old feed at the rate of 2 - 5 % of their average body weight per day.
• Fish older than 90 days feed at 3 % of their body weight per day

Very roughly 1 mm of fish length may be equivalent to 1 gm in weight but this varies from species to species. In some species length in mm is equivalent to age in days

To calculate the amount of food required per day:
(Average weight of fish in grams x number of fish) x (figures above)/100 = grams of food to feed per day.
 

Example
fish average weight 50 grams, 100 fish, age 60 days and using 5 % body weight as daily feeding rate.
50 x 100 X 5/100 = 250 grams of food per day
 

• Try to spread the feeding over 24 hours - a small amount of food at each feeding time will help you keep control of your water quality.
  
• If using feed as a supplement to natural feed in a pond or dam then feed half the calculated amount required for a recirculating aquaculture system.
  
• The weight gain of the fish over a period can be estimated if the food conversion ratio (FCR) is known. Food conversion ratio is the relationship between the amount of food eaten by the fish and the weight increase of the fish.
  
• Many fish species that are grown out for human consumption have food conversion ratios (FCR) better than 1.5 : 1 that is for every 1.5 gram of food eaten by the fish their weight increases by 1 gram.