How to estimate the biomass of a koi pond?

Knowledge of the fish population in a pond may be necessary when you want to know if you are feeding your fish sufficiently, or when you need to administer treatment via food.

The simplest and most precise method is to weigh each fish individually, but this ideal situation is only possible when the population is small and you have mastered the operations of capturing and tranquilizing the animals.

Most of the time, it is necessary to use an indirect method:

By sampling

• Divide the number of your fish into 2 to 4 groups according to their size;

• Catch one or two representative specimens from each group, then weigh them;

• For each group, multiply the average weight found by the number of individuals in the group.

By the size of the fish

• Divide the number of your fish into 2 to 4 groups according to their size;
• Catch one or two representative specimens from each group, then measure their total length;
• Evaluate the estimated weight of each fish captured using the table below;
• For each group, multiply the estimated average weight by the number of individuals in the group. Total lengthEstimated weightNormalSkinny (-10%)Large (+10%)10 cm****21 g19 g23 g15 cm****67 g60 g74 g20 cm****154 g138 g169 g25 cm****292 g263 g321 g30 cm****494 g444 g543 g35 cm****770 g693 g847 g40 cm****1130 g1017 g1244 g45 cm****1587 g1428 g1746 g50 cm****2150 g1935 g2365 g55 cm****2829 g2546 g3112 g60 cm****3634 g3271 g3998 g65 cm****4576 g4119 g5034 g70 cm****5665 g5099 g6232 g75 cm****6910 g6219 g7602 g80 cm****8322 g7490 g9154 g

You can use this tool for your calculations: Excel spreadsheet (XLS)

By the quantity of food distributed

If you have a good idea of the rationing rate of your fish, you can make the following estimate :

Estimated weight (kg) = 0.1 x Quantity of feed distributed per day (g) / Rationing rate (%)

Example: if you distribute 600 g of food per day, with a rationing rate of 1.5%, then the fish biomass must be 40 kg.

Koi carp are generally fed between 0.5 and 2% per day (depends on the age of the fish and the season).