Care for koi and goldfish fish – From egg upwards

One of the many joys of gardening is that many rewards are available to anyone, whatever the level of interest or input may be on an individual basis. Interests in gardening may range from weeding the borders and cutting the grass to keep appearances tidy, through to growing fruit and vegetables to supplement the weekly trip to the supermarket.

The challenges and rewards are incredibly diverse, whether it is controlling moss to achieve a bowling green lawn or propagating and cultivating new varieties of plants from seeds or cuttings. We can even cultivate a garden to encourage transient wildlife to take up residence. Trees can be planted, bird boxes and feeders erected all in the quest to add another dimension to the lives of birds and other wildlife and those of ourselves. What better reward could there be than to think ‘My efforts may have lead to new life taking up residence and perhaps rear their young in my garden’.

There are parallels in the water garden.

Ponds can offer many rewards to their keeper, irrespective of what their ambitions for size, design and planting of the pond may be. In a similar fashion by which birds can be encouraged to take up residence, nest and produce young in our gardens, fish too can be encouraged to breed and produce additional offspring for our ponds. A further benefit is that unlike birds, any homebred aquatic additions to the pond are ours to keep and enjoy, being safely retained within the boundaries of a pond.

Breeding fish in a garden pond, besides being a free source of fish can also enrich the water gardener’s life. They offer the fulfilment of brining new life into a pond, the sheer intrigue gained by watching the development of these homebred fish endeavouring to work out what variety they are likely to be, and which fish in the pond are likely to be their parents.

What does it take to assume the role of a surrogate mother (or father), successfully breeding and growing on homebred fish in a garden pond?. The process is a logical one and if the pond and fish are prepared sufficiently well, then success can be achieved by assuming quite a passive role, letting nature take its course with these ornamental beauties.


Most ornamental fish are very closely related and despite their apparent differences in shape, size and colour are quite compatible with each other. All goldfish varieties, ranging from the common goldfish through other colour variations of the blue shubunkins and the fancier-finned varieties will interbreed, as they have all been selected from the same species. Just as different cats and dogs will interbreed to produce moggies and mongrels which just like fish, will test even the acutest of powers of deduction when trying to identify their parents. Homebred pond fish can prove to be a real Heinz variety!

Fish will breed in ponds during late spring and early summer, in response to lengthening days and warming water. Mature females (whether goldfish, orfe or koi) will begin to swell up, becoming plump with eggs, while males remain trim, more agile and alert, tending to dart through the water with greater energy. As the eggs within the females begin to ripen, ready for spawning, the females release pheromones into the water that the amorous males (which rarely require much encouragement) will find irresistible. The males will swarm around any ripe female (an even some non-ripe females), nudging, bumping and bashing any fish that is suspected as being a female ready to spawn. A pond should be prepared to cope with this physical event by being heavily planted with submerged aquatic weed, such as Elodea and Hornwort. Try to remove as may sharp or abrasive corners or edges and place planted baskets where they may not cause females to come to harm. Spawning behaviour can last over several days, with the more intensive chasing activity occurring for an hour or so each day. During these bouts of spawning activity, the fish appear oblivious to the dangers of being injured on sharp corners or edges, and can often be left with damaged flanks and fins.

All female pondfish being members of the carp family will release thousands of tiny translucent adhesive eggs which will be expelled as the females dive in and out of dense vegetation. It may be necessary to remove females once they have spawned as the persistent attentions of eager males will only further exhaust and stress ‘spent’ females.


Once the eggs have become attached to the various submerged surfaces, assuming they have been fertilised by the males (of whatever variety) they will begin to develop, hatching into larvae after 4-5 days. Even at this stage, it is quite common to be oblivious to the presence of thousands of tapioca-like eggs nestling in the weed. For this reason, always try to provide an area of dense planting, particularly in the shallower areas, as this will provide good spawning area whether you are ready or not.

Carp release so many eggs because of the low odds of producing a mature carp from a single spawn. Fortunately, this means that if we offer even a little extra support for the eggs and fry over and above what they would ‘naturally’ be afforded, we are likely to be rewarded with a good number of fry.

Perhaps one of the most surprising hazards for fry are other fish in the pond (including their parents) which, despite their scavenging lifestyle, will sooner eat one of their offspring than any other aquatic livefood. Dense planting serves a further purpose after being used as a spawning media by providing a refuge or ‘nursery area’ for these tender little fry. Submerged weed will provide fry with a safe bolt-hole as well as a labyrinth of surfaces on which to graze and gain essential nutrients.

Several weeks after hatching, the fry become bolder as they increase in size and courage, venturing more frequently out of the safety of the vegetation. It is common for new fry to be seen for the first time at this stage. They are still likely to be displaying distinctively non-ornamental livery, blending in with the subtle colours of their surroundings and because they make good use of nature’s camouflage, it can be common to become overrun with 1″ naturally-coloured fish. If this is the case, then a decision should be made which will improve the growth rate of all the new-born fry. The more fry the slower their growth rate, and if your new members of the family are going to become permanent fixtures, they need to attain as large a size as possible prior to the autumn to stand a better chance of over-wintering safely. Fry growth can be enhanced through thinning their numbers and passing on those that are surplus to other pond owners.

The race against time.

As most fry, besides being a surprise occurrence in a pond, will be produced in June or July in a garden pond, they will only have 10-12 weeks to reach a size at which they will easily overwinter. The larger a fish can be by the time it stops feeding in the autumn, the greater its chances of overwintering.

Fry growth is also affected by feeding a suitable diet. On account of their tiny mouths and simple digestive tracts, a soft and easily consumed diet such a crumbled flake food is an ideal food. This soon softens up and sinks to tempt even the most reluctant of feeders.

Ponds that are at least 3′ deep will overwinter fish more successfully than shallower ones as they offer more stable water temperatures. The chances of safe passage of your fry through even the harshest of winters can be improved by adding a small pond heater to prevent ice from completely covering the pond.

After winter.

Assuming that you have managed to bring your fish, both old and new, safely through the winter, it is likely that some real changes in the appearance of your fry will start to be observed.

The majority of goldfish fry will not turn ‘gold’ until spring or summer a year after hatching. During this period, as the fish start to feed again, it is likely that some of the previous year’s fry (if they are goldfish) will start to adopt an ornamental finish. Such are the quirks of the genetics of ornamental pond fish that some pond-bred additions may never actually develop the typical ornamental colours of their parents, retaining their ‘back to nature’ brown colouration. It will not be for perhaps another 18 months to 2 years until your homebred fish are mature enough to start their second UK generation, and by that time you should be proud if you’ve been able to grow them to 6-8″.

Desirable features in a garden pond that will improve the chances of rearing homebred pond fish.

Slack water areas. Provide back water areas where fry will naturally congregate and take shelter, away from the every day hustle and bustle of pond life.

Densely planted shelving and shallow areas. Planted nooks and crannies provide vulnerable fry shelter and areas for trouble-free feeding.

Protection from the pond pump. Several models of pond pump are designed to handle solids of up to 6mm. This will include fry. Try to protect fry from pumps by fitting a pre-filter to any such pump so that it will not allow fry to pass through to the pump.

Fry, Juvenile and Adult Fish – Feeding and Susceptibility to Different Diseases.


Fry are surprisingly robust for their size. They have a strong instinct for survival, getting by on food that they can scavenge in the pond. They will benefit from additional feeding of a very palatable flake food when they are a month or so old. Care must be taken not to pollute the pond by overfeeding as at best an inch long fry will consume 1/2 a flake a day.

There are two key threats to fry.

Fungus at the egg stage which can invade from adjacent infertile eggs. However, because so many eggs are released, it is unlikely to wipe out all of the fry.

Once hatched, their second greatest threat is being eaten by other fish, including their parents. Densely planted nursery areas of the pond can reduce the risk of becoming cannibalised.


Juvenile fish can be grown into mature fish by feeding a complete diet, either flake, stick or pellet. It is better practice to offer the fish as large a food size as possible, as this reduces water pollution through uneaten food and will lead to fish gaining better nutrition, growing to adult size at a quicker rate.

Fish of this age are no longer under the threat of cannibalism, but are still susceptible to common diseases which afflict pond fish, such as whitespot, finrot and ulcers. Caused by a range of ever-present pathogenic bacteria and parasites, such diseases are not unique to fish of this age, and can be largely prevented by maintaining a healthy pond environment.

Mature/Adult Fish.

These will be 3 years of age and older, and depending on their size and that of the pond, may have passed their growth peak, with their growth rate slowing down. If the majority of pond fish in your pond are at this stage, then rather than feeding a higher protein growth food, try a lower protein staple diet. This will work out more economical and help in maintaining a healthy water quality as richer foods can increase the burden on a filter.

Adult fish will be susceptible to the same water quality-induced diseases and complaints as the juvenile pond fish. However, around late spring/early summer, watch out for any knocks and bruises on fish that may have been picked up through the physical nature of spawning. Plump females are particularly prone to such injuries.

Kill blanketweed and string algae.