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/Aquatic Gardens, Design, Construction & Maintenance

Koi, Pond Fish Breeding


By Bob Fenner

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon

by Robert (Bob) Fenner

Of all the oxymorons of fishkeeping the statement that "I bred these fishes..." has got to be the most oxymoronic. Really, all that's required to reproduce most pond fish species is a mix of sexes and decent water quality. Ask any experienced ponderer; They'd be more impressed if someone told them their fish had never spawned!

Maybe I'm oversimplifying a bit; let's backtrack and fill in the gaps.


Or maybe which species of fishes are spawned and raised by water gardeners? All sorts is the true answer, with all manner of reproductive modes; the most prominent examples:

The livebearers, that bear their young "live", employing internal fertilization and different types of placental-like attachments for development inside. Little must be done "to reproduce" these fishes other than provide food and cover. These are the mosquitofishes, platies, mollies, guppies, swordtails and more. Each mature female may produce a few to more than a hundred every month and a half or so during the warm seasons.

Egglayers take a different approach, reproducing in several fashions. Some just scatter their gametes given certain behavioral and environmental cues; others are substrate spawners, purposely placing their spawn on a place where, by species, a wide range of parental care is exercised. The sunfishes we call basses, pumpkinseeds, blue-gills et al. are in the last category, and the minnow-like fishes, including koi and goldfish, are part of the former.

Because goldfish and koi are by far the most frequently kept species we will direct the rest of this discussion to their spawning and rearing. Most other minnows (e.g. golden shiners, red-horse) share the same reproductive theme; readers who are interested in other reproductive groups are referred to the Bibliography.


Koi and goldfish may be reproduced most anywhere you can keep them. For control's sake, commercial outfits and advanced hobbyists utilize separate spawning containers. This allows them to pick the spawners, time and place of reproduction, and related advantages of avoiding wear and tear on livestock, as well to ease maintenance in the rearing phases.

Spawning Media:

The eggs of these fishes are adhesive; they really stick to most anything. Oftentimes at koi shows in the Spring and Fall, the combination of new , warmer water and ready conspecifics proves too much and the carp spray their gametes in the display tanks. Oh, the joy of scrubbing off the slimy masses of sticky eggs from the blue vinyl at the end of the show.

Natural and not media are utilized to advantage in stirring spawning fishes to shed their gametes and in collecting them for possible easy removal. Though the fishes will spawn on most anything dangling into the water, purposeful materials used include oxygenating "grasses", water hyacinths, nylon mops, splayed rope segments and much more. I prefer the inorganic substrates as they are easy to clean and store, and don't harbor pests and parasites that might cause harm to the eggs and fry.

The Process in General:

Selecting Spawners:

Goldfish are typically ready to spawn in their second year, koi in their 3, 4th year, sometimes sooner for males depending on their climate of development. Females must receive adequate protein to produce large numbers of viable eggs; but don't worry too much about low numbers. Ten's of thousands cause the ready females to obviously swell when ready.

If practical males and females should be maintained apart; this assures no piscine hanky-panky when you don't want it, and optimized development of brood stock. How to tell boys from girls? The most reliable differences are a matter of relative body shape, females are more broad, round, and widened especially around the abdomen. Males tend to be elongated, more torpedo-shaped; they also develop temporary bony tubercles on their heads and pectoral fins during spawning times.

Though these fish species don't "breed true", you are advised to do what professional breeders do: pick out the best-looking, hardiest specimens to spawn, and keep good notes of the results of your and their efforts.

Preparing the Spawning Container:

Ideally you will use a different container than the main or display pond(s) for spawning. The facility of this option is obvious once you've "had a spawning" elsewhere, you'll understand what I'm getting at. It's so much easier to make massive water changes, feed, and preserve water quality in an independent system. A hybrid approach is to make or buy a commercially made spawning net; this is a large, fine-meshed contraption that floats in the main system.

Goldfish, being smaller than their koi cousins, may be spawned in adequately large aquariums.

About half existing system water blended with new, treated tap is adjusted for water quality, except for temperature. A slightly warmer medium is useful to triggering spawning, just a few degrees F.

The spawning media should be tethered to a given side or corner to keep it in place, as the spawners vigorously thrash each other and all else during "the chase".

Introduction of Spawners:

A female is placed into the spawning container in the early morning and two or three males an hour or so later; this time frame allows you to keep your eye on their progress during the day. Typically males will chase around a female within an hour, and all eggs will have been spent within an hour after that.

Males drive the female into and amongst the spawning media where both release their sex products; with an occasional rest break every few minutes.

Removal of Spawners:

Parents and young are kept apart to reduce predation and maximize oxygen availability. If you're spawning your fish in your main system, or your livestock "just spawn", remove the material they've tacked-up and place it in a grow-out tub of as large a size as practical.

If you've been a smart ponderer and used a spawning tank as suggested, remove the spawners to their original home(s), and check your water quality. Should the water or a good part of the eggs turn cloudy, a large (50%) water change is in order. Replace with system water from the main holding system.

Raising the Young:

The eggs, jelly like blobs develop eyes and tails in about 4-6 days. There are definite things you can do to assure success:

1) Temperature Control: it's very important that the system be at least 59 F, and steady in temperature. This may call for an indoor spawning facility, or the use of a thermostatic heater; at least waiting till the warmer season.

2) Water Quality: Utilizing air-driven sponge filters will go a long way to increasing yield and viability of young by increasing oxygen concentration and removing metabolites. The value of being observant, and diligent in water changing cannot be over-emphasized.

3) Foods & Feeding: A couple of days after hatching, the fry will have absorbed their yolk sacs and start accepting prepared or live foods. Check with local suppliers re these; there are some excellent pre-made offerings and simple methods of culturing infusoria and baby brine shrimp. Feed frequently, if you can, several times per day, of small amounts. Be ever-vigilant about not-overfeeding. With a sponge over the intake, make water changes as often as you can, at least 25% a week.

Rearing on & Culling:

The fry grow quickly and will take crushed flake and pellet foods within a few weeks; this is the time to make the first pass at sorting out the better specimens from those that will be disposed.

Without getting into a philosophical discussion here, let me state that such culling is necessary to provide adequate grow out space and feeding for your livestock. Obviously deformed, colorless, dark-eyed, slow-growing... individuals may be painlessly placed in a pan of water with ice cubes and humanely destroyed by freezing.

Yikes! My Fish Spawned!

Surprise! Without doing a darn thing, your fish have taken matter into their own fins; don't panic. Let's assess your situation: As a minimalist you can choose to do... nothing; some young may make it to adult size on their own; "it's nature's way". If the matter the eggs are adhered to you might want to move it to a separate container (to prevent adult fish from eating them), or alternately move the large inhabitants out.

This common "accident", may be avoided by keeping grass and other dangling plant materials out of your system, but don't count on it. Healthy fishes will spawn sooner or later.

Artificial Breeding:

I do want to at least mention in passing, something re "forced" spawning of fishes. At the low tech. level, ready spawners may be hand-stripped of eggs and sperm ala trout and salmon manipulation. On the high end of the science spectrum, hormones (chemical messengers) can be administered via injection to hesitant broodstock to bring on the behavior and physiology of reproduction (shots to give fish the hots?)...

These alternate methods are the realm of research and fish-farming. They have incident dangers that preclude their usefulness to the casual, though serious apprecionist/hobbyist.


As the saying goes, "This ain't the whole story either"; there are many other ways to spawn pond fishes, and much more art than science to it. The best way to become acquainted with what works is to get a seasoned ponderer to take you under their "fin" and show you first hand how breeding and rearing is done.

Solely reading about such a field seems akin to using the same "way of knowing" for becoming a fine appreciator of jazz.

How to Judge Koi Fish      6/21/15
Hello there,
Just wanted to start off by commending you on all of the great work on http://www.wetwebmedia.com
We've created a website, http://nextdaykoi.com , that we think could offer your audience an additional resource for information about Koi.
It offers broad range of high-quality, live koi and goldfish for sale and is full of useful, well-researched tips and articles—like this one about judging standards for koi: < https://nextdaykoi.com/koi-fish-facts/judging-koi-fish/  >
With all of our great resources and products available to complement yours, we thought that by sharing our site with your audience (or by adding it to the resources/links section of your website, http://www.wetwebmedia.com/pondsubwebindex/pdfshbreefaqs.htm ). you can boost your site's already robust content.
Let us know if we can help you!
Warm Regards,.
<Will add on the morrow. Thank you for your efforts. Bob Fenner>

Bibliography/Further Reading:

Dawes, John. 1991. Livebearing Fishes; A Guide To Their Aquarium

Care, Biology and Classification. Blandford, UK.

Hervey, George F. & Jack Hems. 1948. The Goldfish. Faber and Faber, London.

Jacobs, Kurt. 1971. Livebearing Aquarium Fishes; A Handbook For the Aquarist. T.F.H. Publications, NJ.

Penzes, Bethen & Istvan Tolg. 1986.Goldfish and Ornamental Carp. Barron's, NY.

Pool, David. 1991. Hobbyist Guide To Successful Koi Keeping. Tetra-Press, Germany.

Scott, Peter W. 1987. A Fishkeeper's Guide to Livebearing Fishes; A splendid introduction to the care and breeding of a wide range of these fascinating fishes. Tetra Press.

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon

by Robert (Bob) Fenner
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