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Stocking a 10-gallon aquarium: some new ideas and old favourites for nano tanks
By Neale Monks

Stocking a 10-gallon aquarium with colourful, interesting fish can be difficult because most of the commonly seen fish sold in pet shops really do need more space. But there are some nifty nano species that work nicely in 10-gallon tanks, or for that matter any other small aquarium in the 8-15 gallon size range. You might need to shop around a bit to find all of the fish listed here, but none of them are rare in the hobby.
       
SOUTH AMERICAN THEME

The obvious choices are things Neons, Cardinals and Glowlights, but they’re actually a bit big for tanks in this size category. While you could keep a small school of any one of these in a 10-gallon tank, you’d not have much space for anything else. So here are some better choices for a 10-gallon tank with a South American or Amazonian theme.

Ember Tetra, Hyphessobrycon amandae
This is a small tetra (to 2 cm/0.8 inches) with a semi-transparent body and an overall warm orange colour. While it prefers soft, slightly acidic water this species has proven to be quite adaptable, handling medium hardness water without any problems. It is an active, but very peaceful schooling fish that doesn’t do well with bigger tankmates, but will thrive alongside other small, gentle tankmates such as Pencilfish. Ember Tetras look especially good in well-planted tanks with subdued lighting and dark substrates. They like to swim about in the middle and upper levels of the tank close to floating vegetation.

Pencilfish, Nannostomus spp.
Pencilfish are closely related to tetras but have a narrower body shape, hence their common name. While gregarious, the males sometimes spar with each other so it is important that the aquarium has plenty of plants or bogwood roots that can act as territorial boundaries. Another quirk that you might notice with Pencilfish is the way their colours change at night. Most species get to around 2.5 cm/1 inch in length, though some are a trifle larger. Keep Pencilfish in groups of at least six specimens, and while some species will consume good quality flake, most prefer tiny live or frozen foods.
There are numerous Pencilfish species available, but the easiest to keep and most widely traded is the Golden Pencilfish, Nannostomus beckfordi. It sports black and gold bands along its flanks as well as red blotches on its fins. Having been farmed for many generations now, this species consumes dried foods happily enough and will adapt to moderately hard water without problems. A more intensely coloured species is the Coral Red Pencilfish, Nannostomus mortenthaleri, but this species is usually wild-caught and therefore a bit more demanding in terms of food and water chemistry.

Pygmy Hatchetfish, Carnegiella myersi
Hatchetfish are distinctive fish with very deep bodies and long pectoral fins. In the wild, if they are disturbed these fish use their pectoral fins to help them ‘leap’ out of the water and glide away, hopefully to safety. In the aquarium they rarely do this by choice, even while when the aquarist is cleaning the tank out, but the tank should have a secure hood even so. All the Hatchetfish are nervous and easily stressed, so a nano aquarium with very peaceful tankmates is actually the best way to keep them. One essential factor is floating vegetation of some sort, whether true floating plants or simply normal plants allowed to grow on up to the surface.
The Pygmy Hatchetfish is the smallest member of the group, adults getting to less than 2.5 cm/1 inch in length. Although basically a silvery, semi-transparent fish with a straight black line along each flank, it is so interesting to observe that a group of these schooling fish will give a unique twist to any South American biotope tank. Hatchetfish have hearty appetites: several small meals a day suits them well, and while they do take good quality flake, they really enjoy small live foods that float on the surface, such as wingless fruit flies.

Salt-and-pepper Catfish, Corydoras habrosus
There are several dwarf species of Corydoras that only get to about 3 cm/1.2 inches in length, of which the most commonly traded is the Salt-and-Pepper Catfish. In many ways it’s similar to your standard issue Corydoras catfish, just smaller: gregarious, adaptable, and very peaceful. It isn’t fussy about water chemistry and will happily eat all the usual foods. One way these smaller Corydoras do differ from their larger cousins is a certain tendency to ‘flutter’ about in midwater, even though they prefer to feed on the bottom of the tank. An otherwise very similar species, Corydoras hastatus, is even more prone to midwater antics than Corydoras habrosus. Corydoras pygmaeus is a third example of these miniature catfish. All three species should be kept in large groups, at least eight specimens, and the more the merrier.

Aspidoras pauciradiatus
Aspidoras are closely related to Corydoras but have longer whiskers and are more streamlined in shape. Aspidoras pauciradiatus is the species most often traded species. It has a silvery-white body covered with black speckles, as well as an eye-catching black blotch on the base of its dorsal fin. Aspidoras pauciradiatus is fairly difficult to keep, requiring excellent water quality and a bit of water current, and should only be introduced to a fully matured aquarium. It is completely peaceful though, and a school of 6-8 specimens will work nicely alongside fish that won’t compete for food, such as tetras or Pencilfish.

Otos, Otocinclus spp.
These dwarf suckermouth catfish are inexpensive and widely sold, but in truth they often don’t live for long in generic community tanks. So while Otocinclus are peaceful and fairly adaptable in terms of water chemistry, they do have some specific requirements that have to be met, including good water quality, a reasonable current, ample oxygen, and an algae-based diet (algae flakes and wafers are good for this). If you can meet their needs, you’ll find Otocinclus catfish will get along well with things like tetras, Hatchetfish and Pencilfish. Several species of Otocinclus are available, all much of a muchness in terms of care, but they are social, so do keep them in groups of at least five specimens.


       
SOUTHEAST ASIAN THEME

In recent years there’s been a real explosion in the variety of ‘nano’ fish coming out of Southeast Asia, including the wonderfully colourful dwarf rasboras and the cichlid-like chameleon perches of the genus Dario. There are also some old favourites to choose from too, so aquarists wanting to create a Southeast Asian biotope will find themselves particularly well served by the trade.

Chili or Mosquito Rasbora, Boraras brigittae
Boraras are little gems, barely 15 mm/0.6 inches in length, but with warm red, orange and purple colouration on their otherwise semi-transparent bodies. Boraras brigittae for example has an orangey body, marked with chili-red blotches on its head and fins, and a irregularly-shaped purple band running across its flanks. Boraras brigittae is probably the most commonly traded of the dwarf Rasbora species, and does seem to be quite adaptable and easy to keep in a mature, well-maintained aquarium. It prefers soft, slightly acidic water, but unlike some of the other Boraras species it will adapt to moderately alkaline conditions as well. While Boraras are too small to work alongside larger fish in generic community tanks, they’re ideally suited to well-planted nano tanks alongside other small, gentle fish. They are, of course, schooling fish, just like their larger Rasbora cousins, and must be kept in groups.

Phoenix Rasbora, Boraras merah
Very similar to the Chili Rasbora described above, but the red colouration tends to be more concentrated around the dark markings on its flanks. In terms of care it is a bit more demanding because it will not do well in hard water; instead soft, slightly acidic conditions are recommended, while the addition of peat or blackwater extract will help to show off the subtle colours of this species to best advantage. Like all Boraras, this is schooling species that should be kept in large groups, eight or more, and needs a shady, well-planted tank to feel most at home.

Pygmy Rasbora, Boraras maculatus
This is a slightly more difficult Boraras species to keep than some of the others, requiring soft, slightly acidic to do well. Indeed, a biotope tank with plenty of leaf litter, bogwood roots, and a few shade-tolerant plants such as Cryptocoryne wendtii would provide the best sort of environment. Colouration is variable, but typically some sort of iridescent orangey-pink with one or more black blotches on the flanks, sometimes merging to form a more or less continuous black line, as well as a black eyespot on the base of the tail. Maximum length is around 2 cm/0.8 inches.

Neon Green Rasbora, Microdevario kubotai
The Neon Green Rasbora is another small cyprinid, transparent except for a luminous green stripe running from head to tail, and with a maximum length of little more than 15 mm/0.6 inches. Although these fish are tiny, they’re not especially difficult to keep. The main thing is that they are kept in a reasonably large group, at least eight specimens, and their tankmates are completely peaceful and of similar size. They mix well with Boraras species for example, their metallic green colouration contrasting nicely with the red and orange colours seen on the Boraras. They well take finely powdered flake food, though tiny live foods are certainly appreciated. The Neon Green Rasbora likes water that isn’t too hard, but more important than water chemistry is that the water quality is good water and there is plenty of oxygen.

Galaxy Danio, Danio margaritatus
This Burmese species was formally described in 2007, but since then has become a hobby staple. It is another small cyprinid, with a maximum length of less than 2.5 cm/1 in. Males and females are somewhat similar in having bluish bodies covered with yellow-white speckles, but the males have brilliant orangey-red and black markings on their fins. Sexually mature males are especially brilliantly coloured, and together with their essentially undemanding nature, this has ensured their popularity among aquarists looking for small but attractive ‘nano’ aquarium species. As with most other Danios, this species is fairly tolerant when it comes to water chemistry, bit it does demand good water quality and not too much warmth (22-25˚C/72-77˚F will be fine). Floating vegetation and a gentle current will help this fish feel more at home, and since it is a skittish little fish, you do want to keep a decent school of them, eight or more being recommended. Otherwise this species is undemanding, eating all the usual foods and getting along well with other small, gentle community species. Note that this species is also known as Celestichthys margaritatus and Microrasbora sp. ‘Galaxy’.

Sparkling Gourami, Trichopsis pumila
Sparkling Gouramis are tiny jewels, barely 3.5 cm/1.4 inches in length, but every bit as colourful as any of the other gouramis we commonly keep. With a sort of purplish-pink body covered with iridescent blue speckles, these fish really shine in shady, well-planted tanks with plenty of floating vegetation. In fact this species needs to have plants close to the surface were it can feed and rest, and while it will explore other levels of the tank, it is an obligate air-breather, and like other gouramis, will ‘drown’ if it can’t get to the surface to take occasional gulps of air. Males are slightly territorial, but the small size of these fish means that such interactions are easily managed. So long as the tank has plenty of plants, there’s no reason not to keep a group of them and enjoy their interesting social behaviour.

Moth Catfish, Hara spp.
These South and Southeast Asian catfish are tiny (no more than 4 cm/1.6 inches) and completely inoffensive, preferring to stay close to their hiding places or else burying themselves in soft sand. At night they will come out and forage for tiny live and frozen foods such as bloodworms. Although these catfish are actually denizens of relatively cool, fast-flowing streams, and so best suited to Hillstream biotope set-ups, they can thrive in well-run community tanks provided water quality is excellent and the tank is not too warm (no more than 25˚C/77˚F).

  
SOME OTHER NANO FISH WORTH CONSIDERING

While South American and Southeast Asian themed aquaria are obvious choices if you want to stick to a single biotope, there are other tiny fish out there that might be kept in freshwater systems in the 8-15 gallon size.

Norman’s Lampeye, Poropanchax normani
This widely distributed West African killifish only gets to a maximum length of about 4 cm/1.6 in. Both sexes are silvery-white in colour, with electric blue eyes, but males tend to have more obvious electric blue stripes along their flanks. In schools of eight or more specimens this species is a lovely addition to shady, planted tanks. It is extremely peaceful, and because it stays close to the surface, it’s a useful dither fish when used alongside species, such as Dario or catfish, that stay closer to the substrate. While not difficult to keep in soft to medium hardness water, they are best suited to mature tanks where water quality is good. Note that this species was formerly known as Aplocheilichthys normani, and that Latin name is widely used in aquarium books and websites.

Least Killifish, Heterandria formosa
Also known as the Dwarf Mosquitofish, this North American species is the smallest of the livebearers. Males and females look similar, being silvery fish with an irregular black band along each flank and a distinctive black patch on the base of the dorsal fin, but the males are much smaller, barely 2 cm/0.8 in long, whereas the females get to almost twice that size. While these livebearers are certainly tiny, they aren’t difficult to keep, and under the right conditions will breed quite easily. Like most other livebearers they like water that is moderately hard best, but as North American natives, they don’t want too much heat, room temperature suiting them just fine. What is crucial is that their tank is densely planted, floating plants, like Ceratophyllum, being especially useful. This will provide newborn fry with cover, and provided the adults are not too hungry, you should find many fry survive. What is odd about this species is that fry are born one at a time, a day or two apart, across several weeks. Supposedly females can produce fry up to six months after mating!

Ricefish, Oryzias spp.
Ricefish are small, schooling fish from Southeast and East Asia. Although easy to keep and quite adaptable, their small size and gentle personalities mean they’re not well suited to ordinary community tanks. On the other hand they are perfect choices for well-planted single-species tanks, including nano aquaria, where they work nicely alongside other small, gentle tankmates. The most popular species these days is Oryzias woworae, the Daisy Ricefish, from the island of Sulawesi. It gets to a length of about 2.5 cm/1 in. Males are iridescent metallic blue with red colouration on their throat, pectoral fins, and the edges of their tail fins, whereas the females are yellowy in colour and lack the red pectoral fins. Both have bright blue eyes. Other commonly seen species include the Japanese Ricefish, Oryzias latipes, a subtropical species suited to unheated tanks, and the tropical species Oryzias dancena from India, a silvery-white species with shiny blue eyes and, in the case of the males, attractively ragged dorsal and anal fins edges with white. Ricefish are especially good choices for aquarists with hard tap water, being very adaptable in that regard, some species even occurring in brackish conditions in the wild.