Constipation and stringy faeces in goldfish

Faeces are the most informative thing a goldfish produces and the thing almost nobody looks at until something has gone wrong — which is unfortunate, because by then there is no memory of what normal looked like.

This page covers what the various appearances mean, why round-bodied fancies run into this constantly and single-tails hardly ever, and the point at which a diet problem becomes something a vet needs to see.

What normal looks like

Short, segmented, reasonably solid, dark, and the colour of whatever the fish has been eating. Orange after carrot, green after peas or spinach, brown after a pellet diet. Normal faeces break off and drop rather than trailing behind the fish for hours.

How often matters as much as how it looks, and the appearance alone is what most people try to judge on. A goldfish eating daily at a normal temperature passes faeces through the day, more or less continuously, and how long food takes to travel the length of the gut varies with the temperature and the food. In practice a fed fish should produce something visible within hours, and a colour change after a distinctive meal usually shows up the same day. Judge by the trend rather than a fixed hour: peas fed in the morning turning up green by evening is a working gut, and peas that have not appeared by the next day suggest a slow one.

Temperature moves the whole scale, so judge against the water rather than against the clock. Between 15 and 20 °C digestion is real but slower, and a gap that would worry you in summer is unremarkable. Below about 10 °C it has all but stopped, and a fish that is not passing anything is behaving correctly rather than blocking up; the temperature guide and the feeding calculator both work from the same bands. A fish that has not been fed for a day or two will also trail a thinner, paler strand made largely of gut lining rather than food, which is normal after a fast and is routinely mistaken for the problem this page describes.

Individuals differ, which is why the comparison has to be with the same fish. Fancies pass faeces more slowly than single-tails, a heavily bodied oranda differs from a slim fantail, and none of that is useful unless you know what this fish did last month. That is worth committing to memory — or better, to a photograph, as the healthy baseline page argues — because every judgement below is a comparison.

Reading what you are seeing

What you see	What it usually means
Short, dark, segmented	Normal
Long trailing string, normal colour	Usually just a lot of food; feed less
Long, pale, loose	Food passing through faster than it is digested — overfeeding
Firm unbroken thread, fish straining	Genuine constipation; low fibre, dry food
White or clear stringy, persistent	Mucus rather than food; suspect internal parasites
Jelly-like casts, red vent, fish unwell	Gut inflammation; veterinary
Fine red threads at the vent	Camallanus worms; veterinary
Bubbles in the string	Air swallowed at the surface; switch to sinking food

Two of those rows are the ones that matter for telling the common problem from the serious one. Colour separates them better than anything else: material that is still the colour of the food is food, and material that is white or clear is largely mucus, which means very little is being absorbed.

Duration separates them second. One odd dropping after a heavy meal means nothing. The same appearance every day for two weeks means something.

When the vent itself looks wrong, red and puffy, with threads that come and go, or with tissue pushed out through it, the vent page sorts which of those straining explains and which it does not.

Why fancies and not comets

This is close to a breed characteristic, and the reason is structural rather than medical.

A goldfish has no stomach. Food passes from the throat directly into an intestine that does the whole job of digestion, without a holding chamber — the anatomy page covers the arrangement. In a comet or a shubunkin that tube runs the length of a long streamlined body and works as intended.

In a fancy, the same tube is folded into a compressed spherical cavity, pressed against the swim bladder and against itself. Motility is poorer, transit is slower, and anything that slows it further — dry food, low fibre, cold water, a large meal — has much less margin before it becomes a problem.

Keepers also link constipation with buoyancy trouble, on the idea that a distended gut presses on the organ that controls trim. That mechanism has not been shown, and one aquatic vet doubts that true constipation is a common cause of floating, but a floating fancy and a constipated one can still be the same fish.

Three directions, not one

1. Too buoyant Floats, or ends belly-up at the surface. Air swallowed when feeding at the surface is a common route; a cramped swim bladder, infection or fluid can do the same.
2. Not buoyant enough Rests on the bottom and has to work to lift off. Most often the fish is lethargic from poor water or too little food; a cramped swim bladder, fluid or infection can also be the cause.
3. Cannot stay upright Rolls, lists, tips nose-down or cannot hold a level attitude. Posture alone does not say why; if clean water does not settle it, an aquatic vet can look for the cause with radiographs.

What to do first

Stop feeding for a day or two. This is both the first step of the treatment and half the diagnosis, as fasting and rest days explains. A goldfish is built for an irregular food supply and a short fast harms it not at all; an adult can go several days without difficulty. If the problem was a loaded tract, a rest often clears it on its own.

Then feed fibre, not pellets. A shelled, blanched pea is the standard first move: squeeze the pea out of its skin, which the fish cannot digest, blanch it briefly so it is soft, cool it, and offer a piece or two. Blanched spinach, courgette and similar work the same way, and daphnia provides roughage of a different kind. The vegetables guide covers preparation properly, which matters — a pea still in its skin is an obstruction rather than a remedy.

Check the temperature. A gut in cold water is slow whatever you feed it. If the tank is running below about 15 °C, the answer is to feed less rather than to treat the fish, and the temperature guide covers the ranges.

Then change what caused it. Soak dry pellets until they soften before feeding, which may reduce swelling after they are swallowed. Feed smaller amounts more often rather than one large meal. Build vegetables into the week as routine rather than as medicine. Move a round-bodied fish onto sinking food if it is not on it already.

On peas

The pea is the most repeated piece of goldfish advice there is, and it deserves a straight account.

It is not a drug and it does not cure anything. What it is is soft, wet, high in fibre and readily eaten — exactly what a slow gut with no stomach is short of. The mechanism is plausible, the intervention is free and harmless, and enough keepers have watched it work that it has become the standard first response.

What it is not is a diagnosis. If a fast plus several days of fibre changes nothing, the problem was not a full gut, and continuing to feed peas at a fish with an internal parasite wastes the weeks in which it is losing condition. Give it three or four days and judge by whether anything has changed; a fish that is also getting thinner is the one to take to a vet.

What it looks like when it works

The page above tells you what to do; this is how you know whether it did, because the answer is unusually visible in this one condition.

The timescale. A rest of a day or two clears a simply loaded tract in most cases, and where fibre is doing the work you are looking at two to four days rather than a fortnight. Nothing much happens in the first twelve hours, which is normal and not a reason to escalate the intervention.

The signal is the stool itself. Back to what normal looks like at the top of this page: short, dark, segmented, and falling rather than trailing. A long pale string giving way to short dark pieces is the thing you are waiting for, and it is a clearer endpoint than most fish problems offer.

The other two signs, if they were part of it: buoyancy settling so the fish holds its position without working at it, and appetite returning in a fish that had gone quiet about food.

Partial improvement counts. Shorter and darker than yesterday is the right direction, and it is worth another day before changing anything. Direction over three days beats any single observation, which is the same rule the rest of the health section runs on.

When to stop treating it as constipation. If a week of correct handling — the fast, the fibre, clean water at the warm end of the range — has produced no change at all, then the first answer was wrong rather than slow, and the next section is the one to read. The same applies if it clears and returns within a few weeks: an episode is a meal, a pattern is a diet, and the fix is in what you feed rather than in another fast.

When it is not constipation

Three pictures point away from diet and toward something that needs help.

Persistently white or clear strings on a fish that is eating normally and still thinning over weeks. This is the internal parasite presentation, and such parasites arrive with new fish and wild-caught live food far more often than they appear spontaneously — one more entry on the quarantine argument. Treatment has to reach the inside of the fish: a vet chooses the drug after examining a fresh dropping, usually in food, though a bath is possible for a fish that will not eat — described further on the diseases reference.

Jelly-like mucus casts with a reddened vent, lethargy and loss of appetite. This suggests inflammation of the gut lining rather than a transit problem, and it makes the fish visibly unwell in a way that simple constipation does not.

Swelling with the scales standing out from the body. That is not a gut problem at all; it is the sign described on the swollen abdomen page, it indicates fluid accumulation rather than food, and it is considerably more serious.

Preventing it

Everything on this list is ordinary feeding practice rather than a special regime.

Build the diet on a quality sinking pellet sized to the fish, and soak it briefly before it goes in. Feed small amounts one to three times a day, each gone within a minute or two. Include vegetables two or three times a week as a routine part of the diet rather than as an occasional treat. Give an adult fancy one day a week without food, which suits an animal built for a variable supply. Keep the temperature steady and feed less when it drops. And keep an eye on what the fish produces, so that the first unusual dropping registers as unusual.

A goldfish fed this way rarely meets this page. A goldfish on dry pellets alone, fed generously, in a cool room, meets it repeatedly.