Steve Hopkins

Rain Garden Ornamentals

March, 2005


Anyone who has kept goldfish or koi in ponds for long has found them spawning.  For some itís a nuisance because of the mess it makes and the possibility of the adults damaging themselves in the process.  For others itís a curiosity as the eggs, and then fry, slowly disappear.  In a small pond, adult goldfish and koi will eat most of the eggs and fry and the rest perish from lack of proper nutrition.   It is not uncommon for an occasional goldfish fry to survive and grow up in a pond with the adults if there are enough places to hide and some natural foods available.  However, the numbers are limited and, invariably, it is fish with the least desirable color and fin type which survive.  To find and grow good koi or goldfish, you must start with a large number of juveniles and continually discard the least desirable ones.  Itís a numbers game. 


Described here is an inexpensive live feed method for raising fry.  With some attention and luck, you could end up with a few hundred juveniles which are ready for the first selection.  The method is based on using four plastic tubs of about 15 to 20 gallons each.  The process can be scaled up or scaled down by increasing or decreasing the size of the containers.  You can use four 5-gallon buckets, four 1000-gallon tanks, whatever suits your needs.


Start setting up about a month before you expect the fish to spawn (usually March through June in Hawaii).  Fill two of the tubs with water, add an air stone and add a dozen small tilapia, guppies, or other live bearers.  Feed them about a half teaspoon of crushed flake or powdered fish food daily.  You can also add a pinch of soluble plant fertilizer (the blue one) initially.  Do not change the water.  These two tubs need to receive as much direct sunlight as possible.  You want the water to turn green with microscopic algae (phytoplankton).  You want the tilapia or live bearers to eat all the small water fleas (zooplankton) which could keep the water from turning green.


On the day the fish spawn, you need to start the Moina culture.  Transfer half of the green water from each tub to a third tub.  Pour the green water through a 4 to 6-inch brine shrimp net to make sure there are no baby tilapia or guppies being transferred.  Refill the two green water tubs with freshwater.  Add Moina to this third tub.  Ideally, you would add about 25,000 Moina, or about a quart of water from a dense Moina tank.  Moina can be obtained from a friend who has already started their system, or a commercial source.  Cover the Moina tub with a piece of shade cloth or other fabric to limit the amount of sunlight it receives.  This tub does not have to be aerated.  If an air stone is used, it should be turned down as low as possible.  If the water in the moina tub turns from green to brown, then remove half or more of the water and pour it through the brine shrimp net.  Empty the contents of the net back into the tub and refill the tub with green water as before.  Refill the green water tubs with freshwater.


Also on the day the fish spawn, transfer the water hyacinth or whatever spawning substrate was used to the fourth tub.  It is best to fill the fourth tub with water from the pond where the adults spawned so there is no temperature shock when the eggs are moved.  It is hard to estimate the number of eggs, but you do not want to transfer more than about 500 to 1,000.  Eggs can be transferred on several successive days, but the closer in age the eggs are the better.  Add an air stone to this tub with a moderate air flow.  The eggs will hatch in several days, and it will be several more days before the fry are ready to begin feeding.  When the fry are ready to begin feeding, you will see that they have started swimming about.  At this point, food must be available for them.


On the day that the fry are ready to begin feeding, remove the water hyacinth or spawning substrate.  Then, remove half or more of the water from the Moina tank and pour it through the brine shrimp net.  Try to not stir up the debris n the bottom of the Moina tubójust leave it there,  Empty part of the contents of the net into the tub with the fry and put the rest of the Moina back in the Moina tub.  Refill the Moina tub with green water and refill the green water tubs with freshwater.  Repeat this feeding process every day. 


Ideally, there will always be 15 to 50 Moina per cubic inch in the fry tank during the first few weeks of feeding.  Take a scoop of water with a  white plastic Chinese soup spoon and inspect the contents with a magnifying glass to judge the number of Moina present.  The number of fry should not exceed about a thousand initially and many will not survive.  If there are too many fry, there may not be enough Moina and/or the water quality may deteriorate.


 After a week or so, you will need to begin water changes in the fry tub.  Make a small cylinder of stiff mesh (plastic is best) which will fit inside the brine shrimp net.  Hold or suspend the net with the mesh cylinder in the fry tank and use a short piece of garden hose to siphon water from inside brine shrimp net.  Actually, any fish net will do as long as the fry are not sucked up into the siphon hose.  The amount of water exchange will depend on the number of fry and the success of your Moina culture.  If in doubt, check the ammonia.


 You can begin supplementing the Moina with dry feed at any time.  As noted in the article on page 2-3, you can even eliminate the live feed all together.  If or when the fry begin consuming more Moina than can be produced, a dry feed supplement will make sure they get enough to eat.   However, dry feed which is not consumed immediately may settle to the bottom where it decomposes necessitating higher water exchange.  Moreover, many feel that the quality of the fish produced with live feed is superior.


As the fish grow, more and more dry feed must be used to satisfy their hunger.  The amount and size of the water changes must be increased accordingly.  At some point (usually when the fish are 2 to 4 weeks old) the fish density must be reduced to maintain growth and water quality.  If other space is not available, the green water and Moina tubs can be drained and refilled with freshwater and the fish split between all four tubs with an air stone in each.  Continue with the dry feed and water changes.  Begin siphoning the debris from the bottom of the tubs as soon as it can be done without drawing the fish into the hose.  A sponge filter can also be used.


A key element in raising young goldfish and koi is discarding undesirable fish as soon and as often as possible.  The selection criteria will depend on the variety.  Goldfish can be selected for tail type within a month, but their colors do not develop until they are much older.  Koi fry will either be black or a yellowish white .  Generally, only one color is kept depending on the variety you are selecting for.  Discard every fish with a noticeable deformity (bent back, flared gills, etc.) as the deformity will only get worse as the fish grows.


 Raising fry opens a whole new realm in the goldfish/koi hobby and can be a lot of fun.  Be careful though, its can be habit forming.