Feeding fry and young goldfish

The breeding page makes an argument this page does not undo: a goldfish spawn can run to thousands of eggs, the survivors become fish of 15 to 35 cm that can live for a decade or more, and the decision about where they will all live is one to make before the eggs are on the glass rather than after.

This page is for the two cases that follow. You have made that decision and want to raise them properly. Or a few fry survived in a planted tank without anyone planning it, and you would rather they did well than not.

If it is the first case, breeding goldfish on purpose covers everything that happens before the fry arrive — conditioning, the spawning tank, the eggs — and the year of selection that follows them. Read it before the eggs hatch rather than after, because the one thing that has to be ready in advance is the food on this page.

The timeline

Everything about feeding fry follows from where they are in this sequence.

Stage	When	Feed
Egg	Days 0–4 (warm) to 7 (cool)	Nothing
Hatched, on the glass	2–3 days after hatching	Nothing — living on the yolk sac
Free-swimming	From roughly day 5–7	Newly hatched brine shrimp or rotifers; infusoria or liquid fry food
Week 2–4	Keepers’ practice, not a requirement	Brine shrimp, microworms, finely powdered food
Week 4–8	Keepers’ practice, not a requirement	Crushed flake, ground pellet, daphnia
Week 8+	Keepers’ practice, not a requirement	Ordinary small food, several times a day

The weeks in the last three rows are keepers’ practice, not requirements: offer food small enough for the fry’s mouth, newly hatched brine shrimp or rotifers first, and move to crushed food as they grow, letting the size of the mouth rather than the calendar set the next step.

The first mistake is feeding too early. A newly hatched fry hangs motionless on the glass, on a plant or on the bottom, and is not ignoring the food — it physically cannot eat, because it is absorbing the yolk sac it hatched with. Food added at that point does nothing except decay, in a small volume, at the moment the fry are least able to tolerate bad water.

The signal to start is clear and usually happens across a few hours: they detach and begin swimming horizontally. That is the day feeding begins.

What to feed, and in what order

Infusoria, for the first days. A culture of microscopic organisms — protozoa, rotifers and the like — raised in a jar of tank water with a piece of blanched vegetable or a few grains of rice in it, left somewhere warm for several days until the water clouds. It is free, it is what fry would encounter in a pond, and it is small enough for the smallest mouths. Draw it off with a pipette.

Commercial liquid or powdered fry food. Convenient, available, and it fouls water quickly because most of it is not eaten. Usable, with the water changes to match.

Newly hatched brine shrimp. A very good first food and worth the small effort:

• The right size for a fry’s mouth from day one.
• High in protein and fat at the stage growth is fastest.
• It moves, which triggers the feeding response in a way that a drifting powder does not.
• You can see who has eaten. A fry that has fed on brine shrimp usually shows an orange belly, which keepers use as direct feedback at this stage and which is worth a great deal.

Microworms. An easy culture on a medium of oat or bread paste, producing worms small enough for two-week-old fry. Slightly larger than brine shrimp and a good second string.

Hard-boiled egg yolk, the traditional option: a fragment of yolk squeezed through cloth into the water. It works, it costs nothing, and it fouls water faster than anything else on this list. If you use it, use very little and change water the same day.

Crushed flake and finely ground pellet, as the fry grow; keepers usually start around three to four weeks. Grind it between your fingers until it is dust. The flakes and nutrition pages cover what should be in it; for growing fish, protein content matters.

Daphnia and other live foods once the fry are large enough to take them.

How often

About five small feeds a day for the first weeks, which is what one controlled trial with goldfish larvae used, tapering as the fry grow towards a normal routine.

This is the real obstacle, and it is worth being direct about it. A fry has little reserve, and one held short of food may stay smaller than well-fed siblings — the growth page covers growth in the first years. Fish often catch up partly or fully when feeding improves, but not always, so the sensible course is to avoid long gaps between feeds.

If you cannot feed that often, the fry will probably grow more slowly and more of them may die. That is a constraint to weigh before a spawn rather than a failure to feel badly about afterwards.

The tank they need

Small at first, which surprises people.

Keepers commonly start in 20 to 40 litres, not in something large. Fry do not hunt; they encounter food. In a big tank a cloud of brine shrimp can disperse to a concentration too low for a two-week-old fry to find, and the fry that cannot find food does not grow. A small volume keeps the food where the fish are. You move up as they grow, not before.

Water from the parent tank for the first fill, so nothing about the chemistry is new. Top up and change with conditioned tap water afterwards — the source water page covers what is in it and why a stood, aerated sample is the true reading.

A bare bottom. No substrate. You need to see uneaten food and be able to siphon it, and at this feeding rate that is most of the daily work.

An air-driven sponge filter, already seeded if you have a spare running in the display tank.

A heater with a guard, set around 22 to 24 °C.

A little light, and some plants or a spawning mop. Not for the fry to hide in so much as for the surface film of algae and micro-organisms that grows on them, which fry graze between feeds. Plants earn their place here more than in a display tank.

Gentle surface movement. A heavily fed fry tank uses oxygen, and the aeration guide applies with more force than usual — but gently, since fry are poor swimmers.

How much at each feed

The answer is that you cannot measure it, and there is one piece of direct feedback available.

Brine shrimp give you a readout. A fry that has eaten usually shows an orange belly. Feed until most of the fry in the tank show it, and you have fed about enough — keepers use this as the one direct signal at this stage, and it is worth using brine shrimp for that reason alone.

With powder or liquid food, aim for a faint cloud that has visibly cleared within a few minutes. Anything still drifting after ten minutes was too much.

Siphon what is left, every time, before the next feed. Uneaten food in a fry tank is not a minor inefficiency; it is a main source of the ammonia that can kill a spawn.

Err on the side of feeding, and compensate with water. That is the inversion described above, and the reason a successful fry tank is one where a water change happens daily without being thought about.

What is normal in a spawn

Worth knowing in advance, because a first spawn produces things that look alarming and are ordinary.

Some eggs go white within a day. Those are the infertile ones, which then grow fungus. Remove them where you can, since the mould spreads to viable eggs alongside them.

A proportion of fry are deformed. Bent spines, missing or fused fins, buoyancy that never works properly, eyes that did not develop. In any spawn of several hundred this is expected rather than a sign that something went wrong.

Sizes spread widely by week four. Normal, and the reason for grading.

Colour comes late and unevenly. Covered below.

A great many simply do not make it. In the wild, a spawn of a thousand is expected to produce a handful of adults. A home tank does far better than that and still loses a lot, and a keeper who raises fifty healthy fish from a spawn has done well.

The healthy baseline page applies to juveniles as much as adults once they are recognisable fish, and is the reference for telling an ordinary runt from a fish that is unwell.

The water, which is the other half

Daily water changes, small and gentle, from the day feeding starts. Twenty to thirty percent, conditioned and temperature-matched, siphoned carefully — a length of airline makes a fine siphon that will not take fry with it, and it is worth straining the waste water through a net to check.

A sponge filter is the simple choice. An air-driven sponge gives gentle flow, cannot draw a fry into an impeller, and doubles as a grazing surface. A power filter with an unguarded intake can pull fry in and kill them, and that is a common equipment mistake in raising a spawn; guarded intakes exist, but the sponge is the simpler answer. The same sponge that serves a hospital tank is the right item.

Temperature steady and at the upper end of the comfortable range — around 22 to 24 °C — which speeds growth at the stage where speed matters. Steady is the operative word, as the temperature guide sets out.

Test the water, as you would any tank carrying a heavy feeding load with a young filter.

Do not use the main tank’s substrate. A bare bottom lets you see and remove uneaten food, which at this feeding rate is most of the job.

Growing on: grading and space

Fry do not grow at the same rate, and the difference compounds.

Grade by size, every few weeks. Larger fry take a disproportionate share of the food, grow faster still, and eventually eat the smallest ones — this is ordinary goldfish behaviour rather than anything unusual. Separating them into size groups keeps the smaller ones feeding and is standard practice with any spawn being raised seriously.

Space, which becomes the limit quickly. A hundred fry live happily in a small tank for a fortnight and are seriously overcrowded by two months. The stocking arithmetic applies to them as soon as they are recognisable fish, and growth stalls in crowded water long before anything looks wrong — which the growth page covers as stunting.

The decision nobody writes down

A spawn of several hundred cannot be raised well in the space a hobbyist has. That is the arithmetic, and it produces a decision that serious breeders make routinely and that most guides skip.

Culling. Spawns produce deformed fry, fry with spinal curvature, runts that will never thrive, and — beyond any of that — far more healthy fish than anyone can home. Breeders reduce the number early, and the argument for it is a welfare one rather than a cosmetic one: a crowded tank harms every fish in it, and a hundred stunted adults is a worse outcome than twenty well-grown ones. Where it has to be done, it should be done by a humane method, and it is a reasonable thing to ask an aquatic vet about before you need to.

If you are not prepared to make that decision, the fair conclusion is the one the breeding page reaches: let the adults eat the eggs. That is what happens in any tank of grown goldfish, it happens within hours, and it is a defensible outcome rather than a failure of care.

Rehoming is harder than it sounds. Shops rarely take home-bred goldfish. Friends take two or three. And releasing goldfish into a wild waterway is ecologically destructive and illegal in many places — aquarium release is one of the ways goldfish have spread as an invasive species across much of the world, alongside stocking, bait and pond escapes.

Deciding all of this before the spawn is straightforward. Deciding it while looking at three hundred fry is not.

When a fry becomes a goldfish

Colour. Goldfish hatch olive-brown, which is the wild colouring, and lose it over anything from a couple of months to well over a year. Some never do. It cannot be hurried and it is not a diet problem.

Joining the adults. When too large to fit in an adult’s mouth — which depends on the biggest adult, so judge it generously — and when able to compete at feeding time, which is a separate question. A juvenile that is safe but outcompeted still falls behind.

Food. As they outgrow crushed food they move on to ordinary small food and the routine converges on the normal feeding schedule, with the difference that a growing fish justifies the upper end of it while it is growing.

What goes wrong

Problem	Cause
Fry die in the first week with food in the tank	Fed before free-swimming; the water fouled
Fry alive but not growing	Food too large, or too few feeds a day
Fry disappearing one by one	An unguarded filter intake, or larger siblings
Sudden losses after a good week	Ammonia — feeding rate outran the water changes
Fry gasping at the surface	Oxygen, in a warm heavily fed tank
A wide spread of sizes by week four	Normal; grade them
Almost none survived in the main tank	Also normal, and expected

If you did not plan this

A common way people meet goldfish fry: a planted tank, a spawn nobody intervened in, and three or four survivors that turn up weeks later already a centimetre long.

Doing nothing is a legitimate answer. They will either make it or not, and a handful of fish reaching adulthood in a tank that has room for them is a fine outcome.

If you want to give them a better chance, move them — gently, with a container rather than a net, as the handling guide describes — into a small tank with a sponge filter, and pick up the routine above from wherever they are. At a centimetre long they are past the difficult part, and crushed flake several times a day with daily water changes will do it.

And then, before the next spring, read the breeding page on how to damp down the conditions that set it off — because a pair of goldfish that spawned once will spawn again.