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Goldfish 101: Goldfish May Be Popular, And They May Be Cheap, But That Doesn't Make Them Easy Aquarium Fish


By Neale Monks 



     Just about everything people think they know about goldfish suggests that they're low-maintenance pets that make a great first fish for fledgling aquarists. The reality is that goldfish are among the most demanding freshwater fish in the hobby, especially with regard to aquarium space and filtration. Some would argue that they aren't particularly good aquarium fish at all, and should certainly never be kept in an unfiltered goldfish bowl.


But their low price and wide availability has made them almost the default starter fish for families set up their first fish tank. All too often the excitement at having a new pet turns into frustration as their goldfish gets sick and the water turns murky, until after a few months the poor fish dies unmourned and unloved.

So why are goldfish so misunderstood? Partly, it is their low price. When people pay pennies for a fish, they expect to pay pennies for everything else that goes along with it. Anyone who has ever worked in an aquarium shop will know how difficult it is to convince someone after a goldfish that they need a tank, not a bowl, and that a filter is an essential item, not an option. Far too many people view goldfish as ornaments rather than animals, having seen simple goldfish bowls on television or in books about interior decorating. Worst of all, relatively few people even have any idea how big goldfish get, and assume that small goldfish are goldfish that stay small, little knowing that healthy goldfish can easily exceed 30 cm/12 inches in length.

Water chemistry


Goldfish prefer at least moderately hard water with a neutral to slightly alkaline pH, so the liquid chalk water of Southern England suits them perfectly. The only thing that needs to be added is dechlorinator. Always use a brand that removes chloramine as well as chlorine. A number of water companies use chloramine, and traditional dechlorinator breaks down chloramine into chlorine and ammonia. The chlorine is of course removed, but the ammonia gets left behind, poisoning the fish.

Goldfish do not like soft and acidic water. In such conditions it is a good idea to add something to the system to raise the pH and hardness a bit. Lake Malawi and Lake Tanganyikan salts work very well for this, though you can reduce the dosage to around one-quarter to one-half depending on your local water conditions. The goal is around 10-15žGH and pH 7.0-7.5.

Though often touted as a useful addition to the goldfish aquarium, tonic (or aquarium) salt doesn't do anything to raise the pH or hardness levels. While salt can be used therapeutically for treating certain conditions, there's no reason to use it as a routine additive to the water.

Water quality


Goldfish may tolerate less the perfect water quality for a while, but under such conditions their mortality is still very high.

The water quality parameters to aim for are 0 mg/l ammonia, 0 mg/l nitrite, and less than 50 mg/l nitrate. Now, maintaining these conditions isn't too difficult provided you consider three factors: filtration, water changes, and aquarium size. The goldfish aquarium needs a filter with a turnover about 6Ã- the volume of the aquarium. In other words, a tank containing 140 litres (30 gallons) will need a filter with a turnover of around 840 litres per hour (150 gallons per hour). Anything less and the water is likely to be murky and polluted.

Secondly, you need to perform regular water changes. For goldfish, the more the better, but a good starting point would be 25% per week for toddlers going up to 50% a week for adult goldfish. This will keep the nitrate levels nice and low, and while you are siphoning out the water you can suck up all the detritus from the gravel at the same time. Simply giving the gravel a stir with a pencil will throw the detritus up into the water column quite nicely, but if you want a high-tech approach there are a variety of gravel cleaners available in the shops.

Finally, you need a big aquarium, as much to dilute the waste the fish produce as to give them space to swim around in. For juvenile fish, a 90 litre (20 gallon) tank should be considered the absolute minimum. Adults will need a tank at least 140 litres (30 gallons) in size. It cannot be put any more plainly than this: if you want to set up an aquarium smaller than 90 litres (20 gallons) in size, then goldfish are not an option.



Defining the optimal temperature range for goldfish is somewhat tricky but something between 15-20žC (59-64žF) would be about right. The problem is that while ordinary goldfish do quite well in colder water conditions, fancy goldfish do not. Conversely, while not normally considered tropical fish, goldfish have managed to establish themselves as exotic species in many tropical parts of the world, including Brazil, Madagascar, and Thailand.

Let us consider low temperatures first. Ordinary goldfish ' by which we mean the standard goldfish along with things like Shubunkins and comets ' happily overwinter in garden ponds even under ice. Fancy goldfish ' things like black moors, veil-tails, and Orandas ' cannot be overwintered outdoors and when allowed to get too cold develop problems such as Finrot.

At tropical temperatures goldfish become increasingly sensitive to low oxygen availability. Typically, they will be observed gasping at the surface, a behaviour that allows them to pull the oxygen-rich surface layer of water across their gills compensating for the lack of oxygen in the rest of aquarium. To some degree, this problem can be mitigated by ensuring the water is clean and well aerated, in which case goldfish can be kept in a subtropical or tropical tank alongside such things as rosy barbs or bearded Corydoras catfish, but the water temperature should certainly not be allowed to exceed 25 C ((77 F).



Unlike the majority of tropical fish, which are more or less predatory animals that typically feed on aquatic invertebrates and insect larvae, goldfish are omnivores that consume significant amounts of plant material. Wild goldfish, like carp, root about the bottom of rivers and lakes sifting the mud for decaying plant material, algae, and a variety of small invertebrates such as worms and midge larvae.

In captivity, a diet containing a balance of vegetable and prepared foods is the ideal. When given nothing but prepared foods, such as flake food, goldfish tend to become constipated, evidenced by the long white strings of faeces that emerge from the vent. In severe cases, this can lead to a form of swim bladder disease where the fish is unable to swim properly and has a bloated appearance similar to dropsy. More will be said about curing these diseases later on, but for now the focus is on prevention.

About half the meals you give to your goldfish should simply be more or unprocessed plant material. Much of this can come from the kitchen. Cooked rice, blanched lettuce, canned or cooked peas, sushi Nori, spinach, and so on will all work well in this regard. Certain aquarium plants are also enjoyed by goldfish, and these can be used as a salad bar of sorts, left in the tank for the goldfish to graze on. Pondweed (Elodea and Egeria spp.) are the traditional options for this, but duckweed (Lemna spp.) is enjoyed too.

Perversely perhaps, standard issue goldfish flake and pellets should be used more as a treat than a staple. Most are based primarily on meat- and fish-meal, and these simply don't provide the amount of fibre that goldfish really need. A far better choice is to use vegetarian flake food of the type sold for livebearers. Typically made using Spirulina protein, this algae-based flake is readily accepted by goldfish and makes an excellent staple.

Live foods such as daphnia and bloodworms, or their frozen substitutes, make excellent supplements, but these should be used carefully, no more than once or twice a week. Balance the diet in this way, focusing on plant foods, and not only will you spend much less on fish food, but you'll also have much happier, healthier goldfish!

Social behaviour


Goldfish are schooling fish, so just like neon tetras and tiger barbs, goldfish should be kept in groups. Three specimens is a good number to work with, but the more the merrier. Goldfish are never territorial and exhibit no aggression towards one another under aquarium conditions. The only issue to consider when mixing goldfish is that fancy goldfish don't always work well with their more robust non-fancy cousins. As a rule, all the non-fancy varieties get along well, and in a large aquarium black moors can be added to the mix as well. But Orandas, celestials, and so on are best kept in single-variety aquaria so that there each fish can feed properly and doesn't run the risk of being damaged by a faster or more boisterous tankmate.

Goldfish also make excellent companions for other coldwater or subtropical fishes of comparable size. Relatively few coldwater fish are routinely traded because of DEFRAY regulations on species that could become established in British waters, but the charming weather loach Misgurnus anguillicaudatus makes an excellent addition the goldfish aquarium. Rosy-red minnows, Pimephales promelas, also work well. This said, fancy goldfish are probably best kept alone because they are vulnerable to casual nipping and aggression as well as being unable to compete with more active fishes at feeding time.



Goldfish can suffer from all the same ailments as other aquarium fish, but three stand out as particularly common: Finrot, constipation, and swim bladder disease.

Finrot is caused by a number of different bacteria that nibble away at the fins. It almost always occurs in tanks with poor water quality. During the early stages, Finrot manifests itself as a white, grey, or red fringe to the fins working its way inwards, leaving the fin rays intact. The symptoms of Finrot can be easily treated using off-the-shelf medications, but it is important to remedy the water quality issues as well. Do an ammonia or nitrite test to establish whether or not water quality is to blame, and if it is, take remedial action. A set-up that was acceptable for your fish when they were small may now have outgrown its usefulness, in which case an upgrade will be on the cards.

Constipation is almost always caused by excessive use of prepared flake or pellet foods. This is best remedied in the long term by changing the diet to one containing more plant material, but in the short term stop using flake and pellets altogether and concentrate on high fibre foods such as cooked peas.

Swim bladder disease can be treated in the same sort of way, but you may need to take more immediate action to clear out the gut. Stop feeding the fish for a few days and add a dose of Epsom salts to the water at a concentration of 1.5 tablespoons per 50 litres (11 gallons). This will act as a mild laxative and help loosen up the gut, helping clear things out. Once the fish has recovered its poise and swimming ability, start feeding again but in small amounts and with the accept on plant, not animal, foods.

It should be mentioned that fancy goldfish are especially vulnerable to swim bladder disorders, presumably because of their distorted skeletons and internal organ arrangement.

Choosing your goldfish


You can divide goldfish into two basic types, the ordinary or single-tailed goldfish varieties and the fancy veil-tailed goldfish varieties. Almost without exception, the ordinary varieties of goldfish are more robust and easier to keep. The standard issue common goldfish is a lovely animal and surprisingly variable, and in any one batch you will see fish that range in colour from greenish-brown to coppery pink, with every shade of orange and golden-yellow in between. They have a solid build similar to wild carp or barbs, though lacking barbels of course, something that sets them apart from the superficially similar koi carp. Some fish will be uniformly coloured, while others will sport patches of green, black, or white.

Shubunkins are similar in shape to common goldfish, but have are banded with orange and white patches and covered in lots of black speckles. Despite their exotic appearance, they are just as robust as common goldfish and do well in ponds as well as large aquaria.

The comet is a long-tailed version of the common goldfish, and widely known for being the greyhound of the goldfish family, being capable of astonishing bursts of speed. Of all the goldfish traded, this is the one species that really does thrive in a pond environment where it has space to swim.

Fancy goldfish typically have bifurcated tails, rounded bodies, and a distinctly arched spine. Among the fancy goldfish, the black moor is a perennial favourite, with its greenish-black body and weird, google eyes. While a charming animal in many ways, as with all the fancy goldfish, it simply isn't a hardy animal, and responds positively to all the care and attention you can spare. But in a clean, well-maintained aquarium it can be relied upon to do well and mixes happily with even the non-fancy varieties of goldfish.

The Oranda has a squat, orange body and an impressive raspberry-like growth around the head and eyes. It is somewhat less hardy than the black moor and best left to aquarists with a bit of fishkeeping experience. The same goes for the Ranchu and lionhead varieties, which are similar but lack dorsal fins and have turned-down tail fins that make them awkward, clumsy swimmers. These delicate fancy goldfish are all best kept in their own tank where they can be cosseted to the degree required to stay healthy.

Of the bizarre and challenging bubble-eye and celestial goldfish, it may well be that these varieties cross the line from unusual into grotesque. Bred to have upwards-pointing eyes, they cannot forage about on the bottom normally as goldfish prefer to do, and the bubble-eye goldfish is further encumbered by a pair of fluid-filled sacs beneath the eyes that are easily damaged and quickly become infected should that happen. Delicate and difficult to keep, they are strictly for experienced aquarists.

Whichever goldfish you go for, just remember that these aren't ornaments but pets. Goldfish are easy to tame and quickly learn to recognise their owners. Well cared for, they can live for twenty years or more. It is hard to think of any freshwater fish that offers so much colour and personality, and yet has had to suffer so much abuse.


Info box 1: Top tips for goldfish keeping

Don't mix non-fancy and fancy varieties in the same aquarium.

Goldfish prefer hard, slightly alkaline water conditions.

Choose a filter that offers a turnover six times that of the volume of the aquarium.

Provide a mixed diet, with the accent on plant, not animal, foods.

Don't clutter up the tank with ornaments and plants; keep things simple so you can siphon out waste and maintain optimal water quality.


Info box 2: Top goldfish myths

They do well in bowls. Oh no they don't! Goldfish need a large tank with a good filter.

Goldfish are stupid. They really aren't. Goldfish are widely used in animal behaviour experiments in labs, even being able to learn their way around mazes!

Goldfish have no memory. Wrong. Among other things, they are able to recognise individual humans, learning which ones are likely to provide food.

Overfeeding kills goldfish. Nope. What kills fish is polluted water, which follows on from putting too much protein-rich food in the water. Let your goldfish fill itself with high-fibre greens instead.

Goldfish need salt in their water. Salt helps reduce the toxicity of nitrite and nitrate, but in a properly maintained and filtered aquarium, it is redundant.

New Print and eBook on Amazon

Goldfish Success

What it takes to keep goldfish healthy long-term

by Robert (Bob) Fenner

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