There are many components of a backyard pond but the basic elements boil down to water, fish and aquatic plants. Of course, every pond must have water but the other two are not required for everyone. 

Fish add another wonderful dimension to a backyard pond. Watching them glide effortlessly through the water is a soothing sight. They can become pets and you will soon get to know each individual on sight. 

However, the addition of fish into the backyard pond adds to the complexity of the ecosystem. Fish are living, growing, changing organisms. They eat and breath and they discharge waste products into your beautiful pond! Those waste products are nutrient rich and, if not balanced out, they will contribute to the growth of algae in the pond. In extreme cases, if the wastes build up, they can actually deprive the fish of needed oxygen and kill them too.

When first introducing fish to the pond, put the fish still inside their sealed bag into the pond allowing 15 minutes for the temperature to equalize between the bag and the pond before releasing the fish. If it is a sunny day cover the bag to prevent overheating.

How many fish are too many?  

Unfortunately, there is no single answer to this question. You see some generalizations such as 1 inch of fish per 3 to 5 gallons of water. According to this calculation, a 200 gallon pond (very small) could accommodate 4 ten inch long fish. By extrapolation, a 2000 gallon pond (not huge) could have 40 ten inch fish. Of course, they would not be able to move very much without bumping into each other!

The lesson here is to beware of such generalizations. In determining how many fish to have in your pond, consider the following factors:

Filtration: Since more and bigger fish are going to produce larger volumes of waste, one factor of the carrying capacity of your pond is the type of filtration you install. If you do not use any filtration, the pond system must take care of the waste on its own. Aquatic plants will use some of it but, in almost all cases, algae will move in to use up the rest. Too many fish in this situation and you will have pea soup before you know it.

Use of basic biofiltration as part of your water circulation system will allow you to increase your fish population and avoid pea soup. This generally includes some type of waterfall which will add to the oxygen content of the water.

If you are really serious about the fish part of your pond, you will install a much more elaborate filtration system. It will run the water through several containers which will extract large quantities of the nutrients and other chemical byproducts produced by the fish. These systems can be expensive and require upkeep. However, if your goal is to produce those huge, award winning koi, these more elaborate systems are a must.

Pond Depth: You need to have at least 18 inches of water to even think about keeping fish in a pond year around. Generally, the deeper, the better. Shallow water warms up quickly but it also cools down quickly. Temperature change is one factor that leads to fish stress and disease.

Deeper water moderates the changes in temperature. It is also better for overwintering fish at the bottom of the pond. Deeper water makes it harder for critters such as raccoons and herons from catching the fish for a snack.

Your Willpower: As living creatures, fish know about the birds and the bees just like other animals. Suddenly one spring, your 4 ten inch fish are joined by 10 more one inch long fry. They begin eating and start to add the inches. Then comes the dilemma. 

You already figured that your pond could only handle the equivalent of 4 ten inch fish. Now you have 10 little guys who will soon be bigger guys. What do you do?

If you just ignore them, before long, you will see an increase in the algae in your pond. You will see more fish die over the winter. You might also begin to see diseases rear their ugly heads.

So, you need to remove some of those fish. If you are lucky, you will have friends who are just starting a pond and can use some free fish. More likely, they already have more than they need too. What then?

DO NOT DUMP THE EXTRA FISH IN A POND OR STREAM IN A LOCAL AREA OR ANYWHERE ELSE!!!!!! Many of the fish we grow in ponds are not native to the U.S. and their release will result in one of two things. Either they will live and begin competing with local species or they will die because they are not adapted to local conditions.