By Carolyn Weise, Ecological Laboratories, Inc.

There are different schools of thought, and several ways of defining how many fish can fit into your pond safely. Taking into consideration that a healthy fish, especially koi, will grow each year, your last year’s figures will be wrong by now. Eventually, Mother Nature will thin out an overcrowded pond! In order to prevent loss of your favorite fish, we have a couple of easy ways to figure out how many fish you can expect to SAFELY keep in your pond.

Figuring in the vast differences in filtration units and gph pumps on the market, you may again be tempted to put one or two more fish into the pond than is necessary, but when the power fails, you will find out if that was really SAFE.

Now, if you are not a person who wants to take time fiddling around with filters, water test kits, and the rest, please use your own discretion and put less fish in the pond. If on the other hand you are always doing something with the pond and love being a part of the daily maintenance, you will perhaps be able to stock more fish. Good water quality and thorough pond maintenance are key to koi survival rates.

According to Mid-Atlantic Koi Club’s book, “From the Pages of MAKC News”, the number of 12” equivalents is as follows:

6 inch koi 0.1

8 inch koi 0.3

10 inch koi 0.5

12 inch koi 1

14-16 inch koi 2

18-20 inch koi 5

24-28 inch koi 12

Thus, one 12 inch koi equals ten 6 inch koi and one 14 inch koi equals 125 3 inch koi in loading the pond. Doubling the length of the fish causes roughly a ten-fold increase in the pollution rate. This is why a properly stocked pond can become vastly overcrowded in just a year or two as the fish grow to a larger size.

Overcrowding reduces oxygen levels, increases the number of bacteria and parasites, causes greater variation in feeding… and causes release of pheromones—one of them suppresses the immune system of weaker fish—another suppresses reproductive functions.

Be aware of compound stress effects. Several small factors can combine to produce really bad results…….”

That tells us why we don’t want to overcrowd the pond, now we need to know how to go about not over stocking in the first place, right?

First, you need to know exactly how many gallons are in your pond system. Then take into consideration what type of fish you are putting in the pond. If you want koi, they grow quickly and size is not necessarily contained by the size of the container.

Here are some suggestions for stocking, per size of koi and how much water it requires:

One 8” koi requires 50 gallons

One 16” koi, equivalent to four 8” koi, requires 200 gallons

One 24” koi, equivalent to twelve 8” koi, requires 600 gallons

HELPFUL HINT: Standard koi are measured from the tip of the nose to the end of the tail. Butterfly koi are measured from the tip of the nose to the start of the tail, not the end of the tail, when measuring the fish.

Another way of looking at STOCKING LEVELS:

No more than one 12” koi per 10 square feet of pond surface area ( which assumes good biological filter and good aeration).

Carolyn Asks: Do you know how big your pond is? Now do you know how many koi you can keep in the pond? An overcrowded pond looks like Manhattan during rush hour. Not a pretty sight. A well-stocked pond is a lovely picture and a picture of health!