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  • Species: Aphanius mento

  • Species: Cyprinella lutrensis

  • Species: Enneacanthus chaetodon

  • Species: Scleromystax barbatus

  • Species: Rosy Barb

  • Species: Corydoras paleatus

A new kind of coldwater fishkeeping: temperate zone fish

Too many aquarists assume that coldwater fishkeeping means goldfish. In fact there’s a wide variety of temperate zone fishes that will do very well in unheated aquaria indoors, even though they won’t survive outdoors in ponds. Ordinary central heating will ensure that the temperate zone aquarium won’t get too cold in winter, and most species will tolerate even the warmest British summer without complaint. In fact for most temperate zone fishes, a natural cycle of cool and warm periods through the year will actually improve their health, bring out their best colours, prolong their lifespan, and prompt them to breed readily in spring.

One reason temperate zone fishes are relatively unknown in the hobby is that recent DEFRA legislation has made it much more difficult for some species to be traded by retailers or maintained by hobbyists. Certain species have been deemed to be potentially invasive; that is, believed to have the potential to become established in UK waters, should they be accidentally (or otherwise) released. Sunfish such as pumpkinseeds and bluegills, once quite commonly traded, are now disappeared from the hobby.

Whether or not such legislation is helpful is for the experts to debate, but some of the more enterprising retailers (such as Wildwoods) have actively sought out alternative temperate zone fishes for the aquarist interested in stocking a coldwater aquarium. Most come from either southeastern China or the Deep South of the US, though a few come from other parts of the world as well.

General maintenance

In terms of care, temperate zone fishes require similar conditions to tropical fish. Unlike goldfish or koi, the smaller species at least are not especially messy animals so there’s no need to provide them with exceptionally large aquaria. That said, most of the traded temperate zone fishes come from oxygen-rich streams and rivers rather than swamps, so good water circulation is essential. In general, a canister filter offering upwards of six times the volume of the tank in turnover per hour is recommended.

As you would imagine, temperate zone fishes do not need to be kept at tropical temperatures. However, most of these fish come from what ecologists consider the “warm temperate” zone, with long, hot summers and short winters that rarely become freezing cold. In terms of European comparisons, places like Spain, Italy and Greece would very much exemplify warm temperate conditions. Obviously Britain doesn’t have this sort of climate, which is why these temperate zone fishes are excluded from the prohibited list of species with the potential to become established in the UK.

Put into practical terms, these temperate zone fishes will usually do well across temperatures from 15 to 25 degrees Celsius, and in most cases the optimal water temperature is around 18 degrees C, slightly cooler in winter, and slightly warmer in summer. For most people, maintaining the aquarium room temperature will produce such conditions without the need for additional heating or cooling.

Water chemistry is generally not a critical factor, though as ever it is worth reviewing the needs of any given species prior to purchase. Most of the North American species will be happiest in moderately hard, neutral to slightly basic water, though a few species prefer soft and acidic water conditions. The Chinese species tend to be very adaptable, and will thrive across a broad range of water chemistry values.

Plants and invertebrates

Many ostensibly tropical plants will thrive in an unheated aquarium, though growth may noticeably slow down in winter. Amazon swords, Anubias, Cryptocoryne wendtii, Java fern, Java moss, Sagitarria and Vallisneria can all be relied upon when decorating the temperate zone aquarium. A few species in the trade are genuinely coldwater species and will do better in an unheated tank than a tropical one, notably Bacopa, Cabomba, Ceratophyllum, Elodea (also known as Anacharis or Egeria), Ludwigia, and Marimo moss balls. In open-topped tanks Acorus as well as various pond plants could also be pressed into service to create an interesting display above as well as below the waterline.

Many of the shrimps and snails in the tropical fish trade actually come from subtropical or temperate zone environments, and provided they are combined with fish that won’t eat them, they can do very well in unheated tanks. Amano shrimps and cherry shrimps both thrive in unheated tanks, and apple snails will do much better in an unheated tank that lets them cool down and rest in winter than in tropical tanks where they commonly expire after only a year.


The fish Americans call “shiners” are minnows that live in a variety of habitats though most commonly streams and rivers. Many species are brilliantly coloured, and being completely peaceful and very easy to keep, make excellent aquarium residents. In fact they are very similar to danios, occupying the same sorts of niches in North America as the danios do in South Asia. Essentially all species can be maintained in the same way, and the only decision the aquarist needs to make is about the size of the tank. The smallest species are only about 7 cm in length, while the biggest species are about twice that.

One of the outstanding species is the rainbow shiner Notropis chrosomus. These iridescent fish have pinkish bodies with shiny patches on the head, dorsal surface and the fins. A golden or coppery band runs along the midline of the flank, and in breeding condition males also display a purple band on top of that. Maximum size is 8 cm, but even in the wild fish 4-6 cm are much more common.

A more specialised shiner is the emerald shiner Notropis atherinoides, a very active, fast moving species that feeds on zooplankton in the wild but readily accepts flake and frozen foods in captivity. As its common name suggests, it is essentially green in colour, though the precise shade varies depending on the ambient lighting. Despite their elegant appearance, they are not in the least difficult to maintain in captivity; good water circulation and ample swimming space are the keys to providing this graceful species successfully.

Another superb species is the red shiner Cyprinella lutrensis, a medium-sized, rather deep bodied species that gets to about 9 cm in length. Mature males are shiny blue with orange-red fins and a bold red band above and behind the pectoral fins. Females are smaller and less brilliantly coloured than the males. These are hardy fish by any standards, and provided the water temperature does not go above 25 degrees Celsius, they can even be combined with subtropical and tropical fish! But they will look their best in an unheated aquarium, and being completely peaceful fish combined well with a wide variety of tankmates. (Please note that the shop you are buying from must hold a licence issued by The Centre for Environment, Fisheries and Aquaculture Science (CEFAS) to sell these fish. Please ensure that you purchase your fish from licenced premises).

The shiners of the genus Luxilus are somewhat larger than most of the others, and though not aggressive, they are predatory towards very small fish and boisterous enough to disturb more retiring tankmates. In other words, they are very similar to large danios or hillstream trout (Barilius spp.) in working best alongside tankmates of moderate size. A good example of the type is the common shiner Luxilus cornutus, a species that comes from Canada and the northeastern United States. This species is iridescent olive green in colour, but from early spring to mid summer the males acquire black and golden bands along their flanks and display red markings on their fins. It is exceptionally hardy, and in the wild will inhabit water that ranges from 4-30 degrees C depending on the time of year! In the aquarium anywhere between 10-20 degrees C will suit it very well.
Barbs and danios

Several barbs and danios can be considered suitable additions for the temperate aquarium provided the water doesn’t get too cold, in most cases these species not appreciating being maintained at temperatures below 18 degrees C for any length of time. Among the barbs, the rosy barb Puntius conchonius and the golden barb Puntius semifasciolatus are both good choices for the community tank, though the rosy barb can be a fin-nipper so shouldn’t be mixed with things like fancy goldfish. On the other hand, both these species are colourful, easy to feed, and willingly adapt to both hard and soft water conditions.

Looking at the danios, zebra danios require similar conditions to the barbs and will do well in tanks where the water doesn’t get too chilly. Beyond that simple requirement these are ideal fish for almost any community tank, being attractive and wonderfully active little things.


The larger sunfish (Lepomis spp.) have all but vanished from the trade, but for the aquarist willing to make an effort to keep them properly, the smaller Enneacanthus dwarf sunfish can be exceptionally rewarding. Not only are they highly attractive and well behaved aquarium fish, they also display very cichlid-like behaviours, particularly with regard to breeding. They are not difficult to keep as such, but none of them do consistently well in hard water, and soft, slightly acidic conditions are highly recommended. Provided with appropriate conditions they are long-lived and interesting fishes.

The black-banded sunfish Enneacanthus chaetodon was once known as the “poor man’s angelfish” though today this fish is a good deal less widely traded (and more expensive!) than the farmed angelfish churned out of the Southeast Asia and Florida. In any case, this is a superb aquarium fish with lovely colouration and very elegant movements. It is particularly well suited to the planted aquarium, and a group of these fish in a tank upwards of 120 litres in size would be as beautiful as anything else in the hobby. Newly imported fish can be delicate and fussy about their food, so it’s worth taking time to acclimate them gently to different water conditions and to lay in a supply of live or frozen foods such as mosquito larvae and bloodworms.

Two other species are sometimes traded as well. Enneacanthus gloriosus is known as the blue-spotted sunfish. When mature the males in particular are brilliantly marked with bright blue or green spots. The banded sunfish Enneacanthus obesus is not dissimilar, but the spots are silver rather than blue, and there are the vertical bands on the flanks are generally stronger than those on mature Enneacanthus gloriosus.


The variety of catfish suitable for the temperate zone aquarium is significant, though species should be chosen carefully.

At the larger end of the size range there are various species of Ictalurus, known in the trade as channel catfish. They are astonishingly hardy and tolerant, and the author has successfully maintained them in tropical tanks alongside Central American cichlids such as jaguar cichlids and red devils. But while easily fed with pellets and seafood, their sheer size (upwards of 50 cm under aquarium conditions) makes them very much fish for the dedicated hobbyist.

But there are numerous small catfish eminently suitable for community tanks. Several cories qualify as subtropical fish and thrive in unheated tanks. For a start, the widely traded peppered catfish Corydoras paleatus will do much better at a relatively cool 18-22 degrees C than anything warmer.

But the best catfish for the temperate tank is unquestionably the bearded catfish Scleromystax barbatus, often still referred to by its old name Corydoras barbatus by hobbyists and retailers alike. Its optimal temperature range is between 15-20 degrees C, making it a prime choice for use alongside shiners and sunfish. Slight variations above and below this range in winter and summer will do harm, and if anything will bring out the best colours in these extremely handsome and distinctive schooling catfish.

Hillstream loaches

These loach-like fish are highly adapted to fast-flowing, oxygen-rich environments. While often put into standard tropical community tanks, they rarely do well under such conditions. But a temperate zone aquarium with lots of water movement is much closer to what they need to do well. That said, these fish do not want cold water, and the temperature should not drop below 18 degrees C for extended periods. An unheated aquarium in a centrally heated home should be adequate though, and kept thus these fish could make interesting companions for fast water shiners and the smaller catfish.

Among the species available that would be suitable for the unheated aquarium are the very attractively marked species Sinogastromyzon wui, Beaufortia leveretti, and Beaufortia kweichowensis, all from East Asia.


While British aquarists might not think of killifish as a temperate zone group, associating them more strongly with Africa in particular, killifish are actually very widely spread across southern Europe, western Asia, and much of North America. Unlike the predominantly annual tropical species, these temperate zone killis live for several years and are often remarkably hardy and adaptable. Indeed, many species have evolved to adjust to sudden and dramatic changes in temperature or salinity.

One of the most widely traded temperate zone killifish is the Florida flagfish, Jordanella floridae. Though often thought of as a tropical fish, this species has a broad temperature range and will do well in unheated tanks down to 18 degrees C. Cooler conditions are easily tolerated for short periods, and summer temperatures above 25 degrees C cause them no harm. Consequently these fish will thrive in most British homes all year around without the need for heating in winter or cooling in summer. In fact their only real demand is for the aquarist to remember these are herbivorous fish, and need a predominantly greens-based diet. Spirulina flake, algae wafers and Sushi Nori all make ideal staples, augmented with bloodworms, daphnia and the like. It goes without saying these fish are excellent algae-eaters for community tanks! Florida flagfish don’t show their best colours when young, but as they mature these fish acquire red stripes on their flanks and blue spots on the dorsal surface. Males and females are very alike, though females have a distinctive black spot on the dorsal fin.

A much more feisty, but arguably even more colourful fish is the Persian killifish Aphanius mento. An extremely adaptable and hardy fish, this species does best between 10-20 degrees C. Temperatures slightly above and below this range will be tolerated without complaint, though they cannot tolerate freezing conditions. While not essential, the addition of a small amount of marine salt mix is recommended, especially in soft water areas; the amount required is not much, 3-6 grammes per litre being ample. Females are brown with blue spots, particularly on the fins, but it’s the males that make the species worth keeping: they are unbelievably beautiful fish with dark blue bodies and fins covered with hundreds of bright blue spots. However, the males are also extremely territorial, and are pretty rough on the females, let alone rival males! To get the best from this species you need to “think Mbuna” and provide a large aquarium with lots of hiding places so that each male can claim and defend his own territory. Ensuring that there are rivals in the tank will encourage each male to keep his full breeding colours on display; kept on their own the males are not nearly so brightly coloured. Swimming space at the top of the tank will give the females somewhere to keep out of the way of any males guarding eggs. Overall, this is a challenging but rewarding species for the more advanced aquarist.


The ricefish Oryzias latipes surely gets the nod as the best miniature species for the small coldwater tank. Often considered a killifish, the ricefish is actually more closely related to the halfbeaks and needlefish. But taxonomic issues aside, this is an easily maintained fish with much to recommend it for the community aquarium. Wild fish occur in a variety of colours ranging from brown to pinkish gold, and there are also golden and albino strains that have been artificially produced. Water chemistry is not critical, but moderately hard, basic water is recommended, ideally with a little salt added (3-6 grammes per litre).

Ricefish are small (barely 4 cm in length) and highly gregarious fish, so should be kept in a large group away from predatory or bullying species. They look their best in planted tanks, and this also works best with regard to breeding. After having her eggs fertilised, the female carries them around attached to her anal fin, brushing them off one by one on feathery plant leaves. The eggs are big, and take ten days to hatch, at which point quite large fry emerge ready to be reared on liquid fry food or finely powdered flake food.


Less frequently seen today than in the past, the North American gars are interesting oddballs for aquarists able to provide them with sufficient space. Several species are traded, but the spotted gar Lepisosteus oculatus and the longnose gar Lepisosteus osseus are perhaps the most regularly available.

Regardless of the species, all Lepisosteus are very similar in terms of requirements, being big, predatory fish that tend to ignore tankmates too large to be easily swallowed. Gar tend to be gregarious in the wild, and in captivity do particularly well when kept in twos and threes rather than as solitary specimens. Different species of similar size mix without problems. Although predatory in the wild, gar are easy to feed in captivity, readily taking frozen foods and even pellets once acclimated to aquarium life. Some species are bred in captivity, and these are particularly good aquarium fish. For the most part gar are hardy and adaptable, and do well across a broad range of temperatures and water chemistry conditions. Several tolerate brackish water, and a few even enter the sea.

However, all these good points aside, the inescapable fact is that many gar are simply huge. In captivity they rarely reach the biggest sizes seen in the wild, but they still remain jumbo-sized fish for giant aquaria. Lepisosteus oculatus is the smallest species under aquarium conditions, but even it can be expected to reach a length 60 cm in captivity, while most of the others will get to between 80-120 cm, albeit across a period of several years. Because gar cannot bend their bodies, thanks in part to their heavy armour plating, the aquarium needs to be big enough that they can turn around easily: adults of even the smallest species will need a tank measuring at least a meter from front to back; bigger species will need even larger quarters.


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