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Temperate fish are becoming more and more popular in now – in part driven by the ever-increasing cost of living, as unlike most of their tropical cousins, these fish are generally quite happy in an unheated tank; at least for most of the year.
This means that there is a decrease in the cost of owning an aquarium over the course of a year, or indeed several years. Even better, is the range of species now available in most fish stores that cater to this preference. Gone are the days when the only temperate options were goldfish species that needed larger tanks and extensive filtration, replaced by various smaller and nano options that bring just as much enjoyment as any true tropical species can.
To help with stocking choices, here’s a few favourites to think about:
Badis badis
A fish species so brilliant; they named it twice. Commonly known as the Chameleon Fish, this species (not to be confused with Dario species such as the Scarlet Badis) hails from India, and gets to a respectable size of around five or six centimetres. Their Indian origins mean that they are naturally highly adaptable to differences in water hardness, and crucially, they are quite happy in temperatures from the mid to low teens, through to the low twenties. For most homes in the UK, this is a pretty comfortable internal temperature, and as such heaters can be considered optional. A relatively shy species, whilst they might look cichlid-like in nature, they are actually somewhat retiring, and can be easily outcompeted. Give them a well structured setup with plenty of caves and hiding places, a slower flow, and plenty of meaty foods such as daphnia, brine shrimp, 
blackworm, and they can make a superb species setup. They can also with some effort be trained to accept high-quality prepared foods such as NT Labs Pro-f Probiotic Tropical.
Betta imbellis
Quite often when we use the term “Betta”, people immediately think of the much more common B. splendens – the Siamese Fighting Fish. This is in fact just one of a whole host of species within the wider family, and unlike its much more selectively and intensely bred, B. imbellis is remarkably happy at temperatures as low as 20 or 21c.
Even more impressively, unlike its cousin, this betta can be kept in pairs of a single male and female, in a tank of about 60L or so. Their general requirements are as you would expect – well planted, shaded, lots of places to rest and take cover, and not too extreme a flow.
Channa andrao
Snakeheads are enjoying somewhat of a surge in their popularity at the moment, and C. andrao is a perfect example of why. A smaller species that only reaches around six inches in length, it absolutely does not need to be in tropical temperatures; and in fact is one of the Channa species that needs what is referred to as an overwintering period where their temperatures are allowed to drop right down . This not only simulates what they would experience in their natural habitat, but it is also considered crucial to their overall health and longevity. Perhaps not a true nano species, and wanting a tank of something in the 3ft range for a single specimen, they are if nothing else a very interesting fish to keep. Unlike others, Channa are often quite interactive and will pay attention to their owners, albeit very much on their own terms. A predatory species, C. andrao makes an excellent choice for feeding NT Labs Pro-f Predator Sinking pellets.
Notropis chrosomus
Commonly known as the Rainbow Shiner; this is a species that seemed to disappear from the hobby for a while but is now becoming available in a wide range of retailers. They are a fantastic species for a temperate or even coldwater setup, with a maximum temperature of around 20-22c, and as low as single digits. Some successful keepers have managed these fish in an unheated garage or similar, even through a British winter.
They are not really a species that should be kept alongside others – their breeding behaviour is rather boisterous and the males can be problematic even amongst their own kind. For a fast flowing riverine setup, these can make a beautiful feature fish for a species-only setup.
Tanichthys micagemmae
The Vietnamese minnow, known by various other pseudonyms are a beautiful alternative to the more commonly seen White Cloud Mountain Minnow. In the wild, these fish are found in wide, shallow environments with plenty of current and flow. These waters rarely get above about 20c, and as such they are a perfect species for an unheated setup. Although they only reach a maximum size of somewhere around an inch to an inch and a half, they are a shoaling fish by nature and should be kept in large groups, and oweing to their riverine origins they are powerful swimmers so should be given a tank with plenty of length for them to enjoy and explore. Just because they stay small does not mean they should be kept in small setups.
Macropodus opercularis
The Paradise Fish is a great alternative to Betta, or for someone who enjoys the appearance of a Gourami-like species. These fish come from East Asia and are found extensively in a variety of different water types across the region. They should be treated as a single specimen fish, and can be fairly combative or aggressive which makes them unsuitable for a community setup, but, crucially they do not need to be kept in a heated aquarium. Some keepers actually keep these fish in setups outside during the summer months where the ambient temperatures in the UK are generally more than sufficient for their needs. This fish has actually been in the hobby for well over 150 years now but has not been seen extensively prior to recent years. A bubble nesting species it also offers a great potential breeding project, with a single male being able to be kept with two or more females in normal conditions.
Trichopsis pumila
One of the smaller gourami species, and quite happy down as cool as 21-22c, it would be a crime to not include this fascinating species on a list of nano fish for consideration. Hailing from slow moving waters in and around the Far East in places such as Cambodia and Thailand, often these waters are peat-stained and rich with tannins. As a result, the PH of those waters is often very low indeed, often too low for a normal nitrogen cycle that we would run a standard aquarium by to exist. Somewhat dimunitive and only reaching a maximum size of three or four centimetres, the Sparkling Gourami should be kept in a species-only setup with a single male and a few females. These setups can be as small as 45 or 50 litres, and should be rich with vegetation and plenty of hiding spaces. With such a small fish, and small mouths, make sure any foods offered are of a suitable size. In this case, The Pro-f Micro Crumb from NT Labs is likely to be a hit.
Elassoma evergladei
A somewhat uncommon fish in the UK, but most definitely one that would be worthy of more attention if you are looking for something truly nano, truly temperate, and truly interesting.
The Pygmy Sunfish is found in and around waterways in Florida in the USA. They stay extremely small, with adults being no more than a few centimetres in size. They are also hugely happy in cooler water – found in conditions as low as 10 degrees celcius which is far lower than most British houses will (hopefully) ever have to see! A single male could be kept with a few females in a tank as small as 40L, but, it is important to ensure that these very shy fish are suitably set up with lots of heavy planting, and plenty of leaf litter and other areas for them to hide in. Quite often they will spend a lot of their time hidden away safely, only coming out for breeding purposes, feeding purposes, or when they are startled or disturbed.
Heterandria formosa
Sticking with fish from North America, the “Least Killifish” as it is commonly known, is a particularly diminutive livebearer species. Native to Florida as well as parts of South Carolina, H. formosa are only going to grow to a size of around 2-4cm and does well in a slower flowing water with plenty of vegetation – the latter being very important if you choose to breed this species. They are of course a livebearer so they will breed freely given the right conditions, but will predate on their fry if inadequate cover is provided. A very hardy species, these fish are happy as cool as 19 to 20 degrees celcius, and is particularly happy when fed with dimunitive live foods, frozen foods, or a good quality nano pellet. Be warned however, this relishing of meaty foods will extend to any shrimp species available, so they would not be great tankmates for anything like Neocaridina.
Boraras brigittae
The Mosquito Rasbora is going to win the award for the smallest fish on this list, with specimens rarely reaching 2cm in size. Endemic to Borneo, the Mosquito Rasbora is most happy when stocked in a very soft, very acidic setup with plenty of blackwater tannins, decaying leaves, twigs, etc to give them plenty of places to hide. These guys are happiest in the aquarium when kept in a large group, and although generally peaceful, rival males (especially in breeding conditions) will spar with one another as is common in many related species. This gives some rather fascinating behaviour displays which can be extremely rewarding for the home aquarist to watch. Another species that is happy as cool as 20c, they would most certainly be best kept as a species-only setup with dim lighting and lots of vegetation. If the desire is to mix them with other species, consider either other nano species that will be suitably calm and laid back, or, larger species such as Otocinclus that are less likely to become troublesome for these stunning little fish.
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