Goldfish pellets: choosing and using them well

Walk into any shop and the goldfish food shelf is a wall of colours and claims. Underneath the marketing, a pellet is a simple thing: ground ingredients bound together, dried and shaped so that a fish can swallow it whole. What separates a good one from a poor one is what went into it, how it behaves in the water, and how you use it.

Why pellets make a sensible staple

Goldfish are omnivores that graze more or less constantly in the wild, taking insect larvae, small crustaceans, plant matter and detritus in whatever proportions the pond offers. No packaged food reproduces that, but a well-formulated pellet is a cheap approximation that keeps for months and takes ten seconds to feed. A pellet also holds together in water better than a flake, shedding fewer fragments into the filter and substrate, and whatever the fish does not eat becomes ammonia.

Staple does not mean sole food. The diet this site recommends is built on a quality pellet, with vegetables several times a week and gel or frozen food as a supplement. Pellets carry the load; the rest adds fibre, moisture and variety.

Sinking, floating or somewhere between

Floating pellets sit at the surface until eaten, sinking pellets drop straight to the bottom, and slow-sinking pellets drift down over ten or twenty seconds, a format many keepers of mixed tanks settle on.

For fancy goldfish, many keepers prefer sinking or slow-sinking food. A round-bodied fish tipping upward to snap at the surface takes in air along with the food, and many keepers link that to the buoyancy problems these breeds are prone to. The evidence is observational rather than controlled, and infection is among the causes of floating, but sinking food costs nothing extra and lets the fish feed in the head-down posture its body suits. Single-tailed goldfish handle floating food without trouble, and in a pond it is the only way to see what is being eaten. The full comparison is in sinking versus floating food.

Why a pellet floats or sinks

Worth a paragraph, because it explains the choice above rather than just stating it, and it is not a coating.

Most floating pellets are extruded: the ingredients are cooked under pressure and forced through a die, and as the mixture leaves it into normal pressure the steam inside expands and sets, leaving the pellet full of tiny air pockets. That is what makes it buoyant, and it is also why an extruded pellet can absorb water quickly and swell.

Sinking pellets are made by compression pelleting, or by extrusion with less expansion, and have a denser structure. They tend to take on water more slowly and swell less, which keepers give as a second reason they suit fancy goldfish — less expansion in a gut that has little room for it.

Two practical consequences. Soaking works because it collapses the air pockets, which is why a minute in a cup sinks most floating pellets. And density varies between brands and batches, which is why the glass test on the sinking versus floating page is worth a minute with any new tub.

Pellet size and the goldfish mouth

A goldfish has no teeth at the front of its mouth; it swallows food whole and grinds it with pharyngeal teeth in the throat. A pellet that is too large gets mouthed, spat out and mouthed again until the fragments end up in the substrate. The usual rule of thumb is a pellet a little smaller than the mouth opening: for a young fancy goldfish of 5 to 8 cm, a fine pellet of roughly 1 to 2 mm; for an adult of 15 cm or more, about 3 mm. If fish of different sizes share a tank, a smaller pellet suits everyone.

Reading the label

The ingredient list runs in descending order by weight, and the first three or four entries tell you most of what you need to know. A good goldfish pellet leads with a named animal protein such as whole fish meal, krill, shrimp or insect meal, or with a mix of those and plant ingredients such as wheat germ, spirulina, pea or kelp. A list that opens with wheat flour, corn or soybean meal and puts the fish meal fifth is mostly cereal and plant protein.

Then look at the guaranteed analysis. Juvenile goldfish need about 29 to 35 percent crude protein and adults no more, though some goldfish foods, grower foods especially, declare 40 percent or above. Fat in the region of 5 to 10 percent is typical. Very high protein is not a mark of quality for a goldfish, because the surplus is excreted as ammonia and the water pays for it.

Wheat-germ formulas are the traditional choice for cool water, and makers call them easily digested when a fish’s metabolism has slowed; no digestibility trial in goldfish backs that, and one major maker’s wheat-germ food carries the same minimum protein as its staple. Pond keepers switch to them in autumn and spring, and many stop feeding below about 8 to 10 °C (46 to 50 °F) as a precaution. The seasonal side of feeding is covered in goldfish water temperature.

What the label does not tell you

Three things worth knowing, because they are the places a mediocre food looks like a good one.

Ingredient splitting. The list runs in descending order by weight, so a manufacturer can push a cereal down it by dividing one ingredient into several. Wheat flour, wheat germ and wheat middlings listed in three separate places may each weigh less than the fish meal above them while together outweighing it comfortably. Read for the pattern, not just the first line.

Crude protein is a nitrogen measurement, not a digestibility one. It tells you how much nitrogen is in the food and nothing about how much of that a goldfish can actually use. A pellet padded with cheap plant protein can show the same percentage as one built on fish meal. This is why the ingredient list tells you more than the analysis panel.

Ash. Often listed, rarely read. It is total mineral, and very high values can mean a lot of bony fish meal. No cut-off is established, so treat it as a pointer rather than a verdict.

And one thing the label genuinely does tell you: the date. Fish food degrades from the moment it is opened, and a tub with two years left on it that has been open for one is not the food you bought. Reading a fish food label goes through the whole panel in detail.

To soak or not to soak

Keepers and vets disagree about this. An aquatic vet advises against soaking because water-soluble vitamins leach out before the fish gets them; keepers soak because a dry pellet takes on water after it is swallowed, so a minute in a cup of tank water lets it expand first and, if it floated, makes it sink. Neither side has controlled evidence. A reasonable compromise is to soak floating pellets briefly when you want them to sink for fancy goldfish, to feed sinking pellets dry, and to keep portions small either way. The quantity matters more than the moisture.

Growth food and adult food

A distinction worth making, because it is one of the few cases where a higher-protein food makes sense.

Juveniles are building a body. A goldfish under about a year is growing fast, and growth needs protein — juveniles need about 29 to 35 percent crude protein, and some foods for young fish and for breeding conditioning run to 40 percent or above. The growth page covers how much and how fast that growth should be.

Adults are maintaining one. Past a year or two, growth slows sharply, protein beyond maintenance is excreted as ammonia, and the diet shifts toward more plant matter and fibre. This is the point to move to a standard adult formulation.

And cool water is a third case. Wheat-germ formulas are the traditional autumn and spring pond food, and makers call them easily digested at a slowed metabolism — feeding through the seasons has the temperature bands, and the point below which many keepers stop feeding.

The practical version: one growth food for the first year, one adult food after that, and a wheat-germ option if the tank or pond gets genuinely cool.

Colour foods

A large part of the marketing on that shelf, and the reality is more interesting than either the claims or the cynicism.

They work by a real mechanism. Goldfish cannot synthesise the carotenoid pigments that produce their reds, oranges and yellows; they take them from the diet and deposit them in the skin. Astaxanthin, canthaxanthin, spirulina and marigold extract are the usual sources, and a fish on a carotenoid-poor diet genuinely fades over months.

What they cannot do is add colour a fish does not have. A pale or white-patched goldfish is showing its genetics, and no food changes that. The accurate description is that a colour food restores and deepens what the fish is capable of, over weeks to months, rather than transforming it. Pale or faded colour covers the other reasons a goldfish loses intensity — several of which are water, light or stress rather than diet, and none of which a colour food fixes.

A dedicated product is optional. Many staple pellets already carry a carotenoid source such as spirulina or shrimp meal.

And the background may matter as much as the food. Keepers report that goldfish pale against a bright, bare tank and darken against a dark substrate and shaded surroundings, which costs little to try — aquarium lighting covers it.

Storage and freshness

Fish food goes off. The fats in it oxidise on contact with air, and vitamins, vitamin C in particular, break down with heat, light and time. An opened tub is best finished within about two months, three at most: the Merck Veterinary Manual advises discarding feed two months after opening at room temperature, and University of Florida extension advice is three months at most. Buy the smallest tub that will last that long, keep it sealed, and store it somewhere cool, dry and dark rather than on top of the warm aquarium hood. Never scoop with wet fingers, since moisture in the tub grows mould, and replace any food that smells rancid or has faded.

Keep the working portion separate

A small habit that solves most of the storage problem.

Decant two or three weeks’ worth into a small, opaque, airtight pot and keep that by the tank. The main tub stays sealed, dark and cool in a cupboard, and is opened once a fortnight rather than three times a day.

What it buys:

• The bulk of the food ages more slowly than the working portion does.
• Nothing wet ever goes near the tub, which is where mould starts.
• The portion is visible. A small pot that is emptying faster than expected is an early sign that feeding has drifted upward, which the overfeeding page is largely about.
• And it is where the measure lives. The bottle cap or quarter-teaspoon that holds the daily portion sits in the pot, so whoever feeds gives the same amount.

What a tub actually costs to use

Worth a paragraph, because price is the reason people buy the cheap food and the arithmetic does not support it.

A goldfish eats very little — for an adult fancy, often a dozen pellets or so per meal. Even a premium tub therefore lasts months, and the cost per feed is negligible against everything else in the hobby. What keeping goldfish costs sets out the proportions, and food is not where the money goes.

The genuine cost of poor food is indirect: more of it can pass through undigested, which means more waste, which means more nitrate and more water changes. Buying the better pellet in the smallest tub you will finish within about two months, three at most is cheaper in every sense than buying a bulk container of something mediocre that will be stale before it is empty.

Functional and medicated pellets

A corner of the shelf worth understanding, because the claims vary from reasonable to meaningless.

Wheat-germ and cool-water formulas are the traditional functional food and are covered above: makers call them easily digested at a slowed metabolism, and no digestibility trial in goldfish backs that.

Probiotic and prebiotic foods contain bacterial cultures or the fibres that feed them, on the reasoning that gut flora affects digestion and immunity. The reasoning is sound, the evidence in ornamental fish is thin, and a food containing them is not worse for it. Treat them as a mild plus rather than a reason to choose a food.

Garlic-containing foods are widely used by keepers to tempt a reluctant or recovering fish, though the evidence for garlic is limited — feeding a sick goldfish covers that case.

Medicated foods are a different category. An anti-parasitic or antibacterial delivered in food reaches the gut, which is where some problems live, and for internal infections it is the usual route, with injection, or a bath for a fish that will not eat, as the alternatives a vet may choose. Two conditions attach to food: the fish has to be eating, which the sickest ones are not; and it should be aimed at something identified rather than used speculatively, for the same reasons set out in using medications safely — every course is a stressor and blind treatment selects for resistance.

What is not a functional claim: “enhanced formula”, “premium” and most of the front of the tub. The ingredient list is where the information is.

Keep a second brand

A small habit that prevents a recurring nuisance.

Goldfish are conservative about food, and a fish accustomed to one pellet will often refuse an unfamiliar one for days — which is a problem the day your usual food is discontinued, out of stock, or turns out to have been reformulated.

Rotating two good pellets, a few weeks on each, keeps the fish used to more than one thing and makes any future switch a non-event. It also hedges against a bad batch, and it adds a little variety to a diet that is otherwise identical every day.

And when you do have to switch, do it gradually rather than abruptly: mostly the old food with a little of the new, shifting the proportion over a week or two, offered at the start of a meal to a hungry fish. The sinking versus floating page covers the method, and the thing not to do is starve a fish into accepting something.

How much to feed

A rule of thumb many keepers use is simple: feed what your goldfish will finish in one to two minutes, once to three times a day, and adjust from there. Watch the fish as well as the tub, whose instructions range from about a minute to five minutes of feeding. If pellets are still drifting after two minutes, reduce the next portion. How often to feed goldfish covers frequency by age and season, and overfeeding explains why too much is a common mistake.

When you are ready to compare specific products, our goldfish food buying guide applies these criteria to what is currently on the shelves.