Feeding a sick goldfish

The health section is full of instructions about food. Stop feeding for three days. Feed lightly during treatment. Treat with medicated food. A fish that has stopped eating cannot take medicated food, though a vet has other routes.

What none of those says is what to actually put in the water for a goldfish that is unwell — which is a different question depending on one thing above all others.

The fork: is it still eating?

Everything below follows from this.

Still eating normally. A good position to be in. Feed less than usual, feed well, and use the appetite while you have it — it is the usual route for medicated food and a useful daily sign that the fish is holding its own.

Eating reluctantly. The case this page is mostly about. A fish that takes food half-heartedly, or takes it and spits it out, or only eats if the food is right in front of it. There is a great deal you can do here, and doing it early matters.

Not eating at all. Not a feeding problem but a symptom, and the loss of appetite page is the right starting point. Test the water first — ammonia, nitrite and a temperature that has dropped are common answers, and none of them is solved by a different food.

What counts as eating

Worth separating, because four quite different problems all get described as “not eating” and each points somewhere else.

Ignores the food entirely. Does not approach, does not react. The classic appetite loss, and often environmental — test the water first.

Approaches, then turns away. Interest is there and something stops it at the last moment. Often a temperature that is too low for enthusiasm, or a fish that is simply not hungry because it is being fed too much on other days.

Takes food and spits it out, repeatedly. This is the informative one. It usually means the fish wants the food and cannot deal with it: a mouth injury, a sore or swelling inside the mouth, gill irritation making the mechanics difficult, or food that is simply too large. Try much smaller, softer food before concluding anything else.

Tries and cannot reach it. A fish with a buoyancy problem that cannot get down to sinking food, or cannot hold itself at the surface for floating food. The appetite is intact and the delivery is wrong — the sinking versus floating question becomes a practical one rather than a preference.

Eats, but loses weight. Covered below.

The healthy baseline page describes what ordinary feeding behaviour looks like, which is the comparison all of this rests on.

Why a sick fish should eat, and eat less

Both halves of that are true, which is why the advice sounds contradictory.

Why it should eat. Healing a wound, fighting an infection and replacing damaged tissue all cost energy and protein — first aid for an injured goldfish covers the feeding side of a physical injury specifically. A fish that eats nothing for a fortnight while fighting something is thinner and weaker at the end of it, and condition is one of the few things on its side. The nutrition page covers what it is drawing on.

Why it should eat less. Digestion itself consumes oxygen, which a fish with damaged gills or in warm water can ill afford. A stressed fish may digest less well, so more food does not mean more nutrition. And uneaten food in a hospital tank with no established filter becomes ammonia within hours, which is the problem you were trying not to add.

So: a small amount of good food, taken within a minute, with the remainder siphoned out. Not a normal ration, and not nothing.

The exception is the group of problems where food may be part of the cause — constipation, buoyancy trouble, an ammonia spike. There a short fast, or cutting feeding right back, is the usual first step, and the fasting page covers how long and how to break it.

Eating well and still getting thinner

The one pattern on this page that calls for a diagnosis rather than a change of food.

A goldfish with a normal or increased appetite that is nonetheless narrowing along the back, developing a visible ridge, or looking bony above a rounded belly may have an internal parasite: food is going in and something else may be using it. But chronic bacterial disease, poor diet and competition for food are also possible. Mycobacteriosis in particular, which can look like this, has no effective treatment and can infect people, so wear gloves when handling the fish or the water. Pale, stringy or clear faeces alongside it may point to a gut problem, and the constipation page covers how to read what comes out.

This is the situation to take to a vet before medicating, because a parasite is diagnosed by smear, biopsy or histology, and which organism is involved changes what treats it. If a parasite is confirmed, medicated food is one route and works only while the fish still has an appetite, so act early.

What it is not: a feeding problem to solve with more food. If a parasite is the cause, a bigger ration feeds it along with the fish. Before concluding anything, make sure the fish really is getting its share; a goldfish losing weight covers telling a fish that loses out at feeding time from one that eats and thins anyway.

Restarting an appetite

Things to try, roughly in the order keepers reach for them.

Live or frozen food. Often the first thing to try. Daphnia, newly hatched brine shrimp, bloodworm or a chopped blackworm move and smell in a way that dry food does not, and they often restart a feeding response in fish that have ignored pellets for days. Live food and frozen food both work; frozen is easier to keep on hand for exactly this.

Warmth, within the range. Appetite follows temperature closely, as the temperature guide explains. A fish at 16 °C is not going to be enthusiastic; the same fish at 21 °C often is. Move it gradually and stay inside the comfortable band.

Soak the food. Softer, more aromatic and easier to take. Thirty seconds in a spoonful of tank water.

Smaller particles. A fish that is weak, or whose mouth is sore, manages small food and gives up on large. Crush a pellet, or move to a finer grade.

Quiet, and low light. Feed when the room is calm and the tank light is off. A nervous fish in a bare hospital tank will not eat with someone standing over it.

Away from competition. In a community tank a sick fish loses every race to the food. Feeding at the opposite end, or feeding the others first, gives it a chance.

Garlic. A drop of garlic extract, or juice from a crushed clove, on soaked food. It is a keeper favourite as a feeding stimulant, and strongly flavoured food is often accepted by reluctant eaters, but there is little evidence on garlic itself in goldfish, and the antiparasitic claims made for it go well beyond what is known. Treat it as a way of making food attractive rather than as a treatment.

Patience, and removal. Offer a small amount, give it a few minutes, and take out what is left. Food sitting in the tank all day is not persistence, it is ammonia.

A fish that has stopped entirely

Two things matter, in this order.

Find out why, the same day. Test the water, check the temperature, look at the fish properly, and read loss of appetite. A goldfish that stops eating is reporting something, and the cause is often environmental.

Then do not wait. There is no evidence-based safe waiting period for a fish that has stopped eating. A healthy, well-conditioned adult can generally go a few days without food, but a fish that is already ill and already thin has less margin, because it is spending energy on being ill. If the water tests clean and the fish is still not eating, look harder rather than wait — and if it is also losing condition visibly, that is a vet conversation.

What it is not is a reason to fast it further. As the fasting page puts it: a fish that has stopped eating is not in need of a fast, because it is already not eating.

What to feed for which problem

Problem	Feeding
Buoyancy trouble, rolling or sinking	Keepers fast 2–3 days, then offer small soaked sinking food; if it persists, look for infection
Long trailing faeces, constipation	Fast, then vegetables and reduced ration
Ulcer, fungus, torn fins	Feed lightly and well; healing needs protein
Suspected internal parasite	A vet diagnosis first; medicated food while it still eats, if a parasite is confirmed
Wasting despite eating	A vet case; diagnosis before any medication
Recovering from ammonia damage	Very light; clean water does the work
During any medication course	Small, watched, siphoned
After a course	Build back over several days
Old fish, declining appetite	Softer, smaller, more often

Medicated food

How it works: a treatment is bound to or absorbed into food, the fish eats it, and the active ingredient reaches the gut and the bloodstream directly.

When it is the right answer. Internal parasites, gut infections, and anything systemic that a keeper can legitimately treat. It is the usual route for internal infections, including the worm and protozoan problems the diseases overview describes as arriving with new fish and live food.

Commercial or home-made. Commercial medicated foods are pre-dosed and straightforward. Home-made means soaking food in a measured solution and letting it absorb, which is how most keepers do it and which depends on following the product’s own instructions rather than a general recipe.

The constraint. It only works on a fish that eats, and only if that fish eats its share. In a community tank the sick fish may get none of it, which is one more reason for a hospital tank. A fish that has stopped eating is a case for a vet, who may use a bath or an injection instead.

The dosing caution. Everything on the medications page applies: follow the product, do not combine treatments, do not halve a dose to be cautious, and finish the course. A prescription-only treatment for a systemic infection means a vet, who can also tell you whether medicated food is the right route at all.

Feeding in a hospital tank

Different from feeding in a display tank, for one reason: there is usually no functioning biological filter, so every uneaten flake counts.

• Very small amounts, once or twice a day.
• Watch it being taken. If it is not eaten within a minute or two, there is no point leaving it.
• Siphon the bare floor after every feed. Thirty seconds, and it removes most of the ammonia load before it becomes ammonia.
• Test daily, and change water on the reading.

The hospital tank guide covers running one that is not cycled, which is most of the work.

Vitamins, tonics and immune support

A plain treatment, because this is an area with more marketing than evidence.

Vitamin C has a genuine basis. It is involved in wound healing, collagen formation and immune function in fish, and deficiency is real. A food carrying a stabilised form — the label page covers which — is worth having for a fish that is healing, and it is one of the few nutritional claims in this area with support behind it.

General “immune boosters” and tonic foods are mostly unproven. Beta-glucans and similar additives have some research interest and a great deal of marketing; none of them is a substitute for clean water and a fish that is eating.

Vitamin supplements added to water do very little. Fish absorb nutrition through the gut, not through the skin, and most of what goes into the water simply feeds the bacteria.

The useful version of this is unglamorous: a good complete food, fresh rather than a year old, fed in small amounts to a fish that will take it.

Afterwards: rebuilding condition

A fish that has been ill for weeks has usually lost weight, and the recovery period is a real phase rather than a return to normal.

Build back over a week or two, not in a day. The gut has been running on very little and a full ration immediately can bring on a buoyancy problem.

Feed slightly more often rather than more at once — three small meals beat one large one for a fish putting condition back on.

Use good food while it matters. This is the point at which protein content and ingredient quality earn their keep, and the nutrition page sets out what to look for.

Expect it to take longer than the illness did. Condition comes back over weeks. A young fish that was ill during its growth period may stay smaller than its siblings; many catch up partly or fully when feeding improves, but not always, and the growth page covers what to expect.

Then stop. A common error in this phase is continuing to feed generously long after the fish has recovered, on the grounds that it was thin once. A recovered goldfish needs an ordinary ration.

The old fish

Worth separating from illness, because it gets mistaken for it.

Keepers often report that appetite falls with age. A goldfish in its second decade that eats less than it did, but still eats, still holds its fins open and still behaves like itself, may simply be old — the lifespan page covers what the last years look like.

What helps: softer food, smaller particles, more frequent small feeds rather than fewer large ones, and a little more patience at feeding time. What is worth investigating is a decline that happens over days rather than months, or one that arrives alongside anything else.

The short version

If it is eating, feed it less and feed it well, and use the appetite while you have it. If it is eating reluctantly, reach for frozen or live food before anything else. If it has stopped, that is a symptom — test the water, read the loss of appetite page, and do not spend the week trying different foods on a fish whose problem is ammonia.