Pond Fish

Stocking Pond Fish and Scavengers

Pond fish can be added immediately after the plants. Check the PH level of your pond first. Koi can survive in water with a PH between 6.5 (slightly acidic) to 8.0 (slightly alkaline). A PH of 7.0 is neutral. If your water is outside of this range you need add chemicals to adjust it. Also check to see that there is no evidence of chlorine or ammonia/nitrite present.  Standard water test kits are inexpensive and the presence on any elements that may be toxic to pond fish can be discovered by dipping a single test strip into the water.


Pond Fish Selection: Koi vs. Goldfish

Any cold water fish can survive in a pond but typically backyard ponds are the homes for koi carp and/or goldfish. I prefer koi which are bigger, more colorful, longer living and friendlier but the fish can exist together. Koi carp will recognize their owners at feeding time and actually learn to swim up and eat from your hand while I have never seen goldfish exhibit quite the same level of familiarity. The goldfish are much less expensive and types such as Comets and Shibunken are  hardier and easier to maintain. Koi and Goldfish can co-exist in a pond and in my first pond I included gold fish with my koi. The goldfish reproduced at a much faster rate than the koi and I belief the goldfish ate most of the koi eggs/fry.  So my other fish ponds have been restricted to koi only and the level of reproduction is much better.  There is more information about these koi on the Breeding Koi page.

 Pond Fish

Koi & Goldfish Together in Pond


Establish the Nitrogen Cycle

The pond fish should be added gradually (once per week, 2 or 3 at a time) to allow the bacteria in the filtration system to build up. The pond fish will add waste to the water which will cause ammonia (nitrites) to build up. The bacteria feed on and breakdown the nitrites into harmless nitrates which are absorbed by the plants. By adding the fish gradually you allow this natural nitrogen cycle to establish itself without the risk of poisoning the water. Excessive nitrites in the water will be fatal to your pond fish. Use the water test kit to continuously monitor the amount of ammonia in the water during this time.


How Many Pond Fish?

The number of pond fish that can be added to a koi pond is a function of the size of the pond and the effectiveness of the filtration system.  A simple rule of thumb is 1 inch of fish per 10 gallons of water. For simplicity, I assume that the average length of koi in my pond at any one time is 12 inches.  On this basis I can keep 8 koi for every 1000 gallons of water in the fish pond. To allow for reproduction and reduce costs, I keep my initial stocking at about 20% – 30% of the total capacity


Initial Stocking of Pond Fish

I usually buy koi in the 3 to 5 inch range since you can get smaller high quality koi for a much better price (under $20) and you  get the pleasure of seeing them grow. They grow very quickly and will reproduce in the proper environment. I purchased a dozen fish for my large (10,000+ gallon) pond. The pond looked pretty empty at first but now 8 years later I have well over 50 fish (too many to count accurately) with some approaching 2 feet in length.


Releasing the Pond Fish

Your pond fish will be in an oxygenated bag. Float this bag on the water for 20 t0 30 minutes to allow the temperature to equalize to the water in the fish pond. Then add some water from the pond to the bag and wait another 10 – 15 minutes to allow the fish to gradually adapt to any difference in PH.  Then gently release the fish into the backyard pond. Wait 24 hours before feeding the fish.


Feeding Pond Fish

During the spring, summer and fall I feed my koi 2x per day (5 -10 minutes each time). I occasionally have to remove a dead fish from the pond but that is about it and feeding the fish is fun, not work. The fish actually recognize me come from our deck when it is feeding time and they excitedly swim up into to the shallow water of the pond to get their food. They take food from my hand as advertised in many books written about koi.


Finally Add Scavengers to Keep the Pond Clean

I utilize three types of scavengers, catfish, pond snails and frogs. The primary purpose of the scavengers is to help maintain an ecological balance by feeding on organic wastes given off by the pond fish and plants, reducing algae growth and keeping the water clear. At least two of them, the catfish and the frogs are pretty cool visual additions too.



I usually add a single albino catfish to my koi pond. This catfish is compatible with koi and grows rapidly. It feeds off the bottom but also can be seen coming to the surface to grab food during the feeding sessions.


Green frog 440 150x150 Pond Fish

Tadpoles quickly turn into frogs


I stock tadpoles and they quickly transform into frogs. The frogs can survive the winter and also reproduce. They eat insects, fish eggs, small fish and smaller tadpoles. They are quite vocal and contribute interesting serenades in the spring and summer particularly during mating season. They help keep the fish population under control and keep the pond environment in balance. Depending on where you live, native frogs may just show up at the pond and there will be no need to stock any.


japanese trap door snail2 150x146 Pond Fish

Japanese Trap Door Snail


Pond snails help by eating algae and decaying organic matter. They generally survive winters and will reproduce so an initial stocking will generally suffice.



How Many to Add?

The general rule of thumb is to add 1 scavenger for every square foot of koi pond surface. Since the scavengers (tadpoles and snails) generally cost $1 to $2 dollars each this can get quite expensive for a large pond so I have gotten by with ½ the recommended stocking level.


Next learn How to Maintain a Pond


 Pond Fish

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