• Source: Neale Monks

    Species: Barilius bakeri

  • Source: Neale Monks

    Species: Devario aequipinnatus and Danio "lemon"

  • Source: Neale Monks

    Species: Schismatorhynchos nukta

  • Source: Neale Monks

    Species: Schistura balteata

  • Source: Neale Monks

    Species: Sewellia lineolata

Life in the fast lane: hillstream fishes

21 January 2011


Hillstream fishes come from fast-flowing habitats, and that means the hillstream aquarium needs lots of water current and plenty of swimming space. Although not the most widely traded of aquarium fish, some of the freshwater gobies and so-called sucking loaches are regularly seen. Specialist retailers including Wildwoods in Enfield, North London and Maidenhead Aquatics at Crowland regularly carry the less often seen species such as Barilius and stonelapping loaches.

Setting up a hillstream tank

Canister filters probably provide the easiest way to generate the water current required, but exactly how you go about this aspect of the hillstream tank doesn’t really matter. Provide at least eight times the volume of the tank in turnover per hour, and ideally at least ten times the volume of the tank. Filters are rated in terms of turnover, either in litres per hour (LPH) or gallons per hour (GPH). This rating should be visible on the pump, but failing that should be quoted in the instruction manual.

For example: an aquarium that had a capacity of 150 litres would need a filter that provides not less than 1200 litres per hour and ideally 1500 litres per hour. You can use multiple filters if you want, or supplement an undergravel filter with a couple of powerheads. It doesn’t really matter precisely how you generate the water current — just that there’s lots of it!

Take care that the flow of water at the bottom of the tank is just as strong as the water at the top. A quick way to test this is to put a few bits of flake on the substrate. If the flakes quickly get whipped away by the water current, all well and good; but if not, then you still have some work to do.

Open water schooling fish like danios don’t do well when they feel cramped. Aim to keep such fish in an aquarium not less than ten times their body length. So giant danios, which reach up to 15 cm in length, would work best in an aquarium 150 cm long.

The substrate-hugging fish like loaches and gobies aren’t so bothered about swimming space, but they do need a complex three-dimensional habitat that will satisfy their territorial demands. Provide them with lots of water-worn boulders and chunky pieces of bogwood. Such materials will also help to evoke the fast water habitat, particularly when complemented with a substrate of fine gravel or smooth silica sand.

Plants aren’t really part of the hillstream habitat, and the fast flowing water will make the use of carbon dioxide fertilisation very difficult. If you want to add some plants, go with robust species with minimal requirements. Anubias and Java fern are ideal, but Vallisneria can look very good too.

Environmental conditions

Water chemistry is relatively unimportant, and most species will do fine across a broad range of values provided extremes are avoided. Water quality, on the other hand, is critical. Few of these fish are tolerant of ammonia or nitrite, so ensure the filter is properly matured before adding these sensitive species.

Temperature is another important aspect, with most hillstream fish favouring relatively cool conditions, typically between 20-25˚C. If the water gets too warm these fish can become heat stressed. Adding additional aeration may help, but in the worst case scenario floating big blocks of ice (made using one litre ice cram tubs for example) can make all the difference.

Danios and minnows

Many species of danio come from hillstream environments. Although often kept in tropical tanks, they do well in the slightly cooler, fast water conditions of the hillstream aquarium. It goes without saying that danios are also wonderfully active and beautifully coloured, complementing the less active loaches and gobies perfectly.

The undoubted king of the danios is the giant danio, Devario aequipinnatus. This beautiful fish should be kept in a group of at least six specimens otherwise it won’t school properly. Although not aggressive or territorial, this species is large enough to be predatory towards very small fish, so choose tankmates with care. Species like White Cloud Mountain Minnows for example are very likely to get eaten!

There are plenty of other danios that would work well in the hillstream aquarium. Pearl danios and zebra danios, Danio albolineatus and Danio rerio respectively, are widely available choices much loved for their hardiness and attractive colours. But any other Danio or Devario would work equally well. Some of the new species on the market, like the glowlight danio Danio choprai, are very attractive fish well worth hunting down.

The White Cloud Mountain minnow Tanichthys albonubes is similar to the danios in terms of care. Considered a coldwater fish by some and a tropical fish by others, it does very well at the middling temperature of the hillstream aquarium.

Hillstream trout, Barilius spp., are similar to giant danios in requirements. They are large fish, typically 10-15 cm in length, with a robust build than makes them look a lot like rainbow trout. Although schooling fish, they are quite boisterous and very predatory. As such these are very much fish for the larger aquarium with similar-sized tankmates. They are very beautiful though, and for the aquarist who has the space for them they make excellent community fish. Hillstream trout are hardy and will eat anything they can swallow, including flake and frozen foods. Kept properly, they grow very quickly, but for some reason reports of breeding in captivity are few and far between.

Stonelappers

The stonelappers, genus Garra, are essentially similar to things like the Siamese flying fox Crossocheilus siamensis but are more strongly adapted to fast-flowing streams rather than lowland rivers. They feed by grazing on aufwuchs, the combination of green algae and small invertebrates that grows on rocks and sunken wood.

In the wild they are gregarious, but aquarium specimens sometimes become quite territorial and are best kept singly. There are multiple species in the trade, though the panda garra, Garra flavatra, is one of the most colourful and tends to work reasonably well in groups provided they are not overcrowded. Garra are usually traded as algae eaters, but they are a bit more omnivorous than that and enjoy algae wafers, catfish pellets and frozen foods such as bloodworms.

Loaches

From the aquarists’ perspective, hillstream loaches can be divided into two sorts: the flattened sucker loaches and the more eel-like stone loaches.

Sucker loaches (not to be confused with sucking loach Gyrinocheilus aymonieri) are small fish noted for their strong dorso-ventral flattening. In other words, they are flattened from top to bottom. They have broad pectoral and pelvic fins, and together with their low profile body this allows them to adhere to rocks and hold their position in fast-flowing streams. Like Garra, they feed on aufwuchs in the wild, but aquarium specimens happily accept suitable alternatives such as algae wafers.

The most common species in the aquarium trade is dwarf stone sucker Pseudogastromyzon myersi, sometimes known as the Hong Kong plec because of its place of origin. It is green in colour with a speckled dorsal surface. While often kept in tropical aquaria they rarely do well there, often dying within a few months. But in the hillstream tank they are active and highly comical fish to watch. They are gregarious but somewhat given to occasional chases, and the aquarist will find their antics highly amusing.

Some species have bred in aquaria. A few, relatively large eggs are placed in gravel nests but are not guarded. After about two weeks the eggs will have hatched and the large fry become free swimming. They will immediately feed on aufwuchs and green algae, and are quite easy to rear.

Stone loaches aren’t able to stick to rocks, and instead use their narrow shape to slither into cracks and crevices where they find refuge from the water current. They only dart out of their homes at feeding time. Stone loaches tend to be rather territorial, though they are most fun when kept in groups. Kept in groups of six or more no single fish will be able to bully all the others. Stone loaches do not reserve their aggression for their own kind, but will also chase other stone loach species. Bigger species could certainly damage smaller ones, so it is best to keep just a single species per aquarium.

Stone loaches are distinctly omnivorous and will accept most aquarium foods with gusto.

Gobies

Although most gobies live in the sea, they are surprisingly diverse in hillstream habitats. Gobies are equipped with modified pelvic fins that form a kind of sucker, and this helps them hold position in mountain streams with ease.

One peculiarity of many hillstream gobies is that while the adults live in freshwater, the juveniles do not. Spawning may take place in freshwater, but the newly hatched fry usually drift downstream and into the sea where they spend a period of time in the plankton. Only once the fry have metamorphosed do they swim inland and up into the mountain streams where they will spend their adult lives. Not all hillstream gobies breed in this way though; the white-cheeked goby Rhinogobius duospilus for example spawns readily in aquaria and the comparatively large fry are quite easy to rear.

Hillstream gobies usually turn up under vague common names rather than Latin names, and identifying many species is extremely difficult. Species of Rhinogobius, Sicyopterus and Stiphodon are the ones most likely to be encountered. Most get to between 5-10 cm and are relatively omnivorous though few have any interest in dried foods.

Close
The hillstream aquarium is a fun challenge for the freshwater aquarist. Although demanding in some ways, hillstream fishes include some real novelties among them, and getting to watch sucker loaches and freshwater gobies at their best is a real treat!

Some notable hillstream species

Dwarf Stone Sucker
Species traded: Pseudogastromyzon myersi
Adult size: 6 cm
Distribution: Hong Kong
Temperature: 20-24˚C
Water chemistry: pH 7-8, 10-20˚dH
Diet: Aufwuchs in the wild; does well on algae wafers and small frozen invertebrates such as bloodworms
Social behaviour: Gregarious but the males are territorial when spawning
Reproduction: Infrequent, but the fry are quite easy to rear
Aquarium notes: Other species of Gastromyzon and Pseudogastromyzon may be encountered, all very similar in terms of care

Sumo Loach
Species traded: Schistura balteata
Adult size: 8-10 cm
Distribution: Burma
Temperature: 22-26˚C
Water chemistry: Not critical, though slightly soft and acidic preferred
Diet: Will eat most frozen and dried foods
Social behaviour: Highly territorial and will chase its own species as well as other similar-looking loaches; keep singly or in groups of at least six specimens
Reproduction: Not reported in aquaria
Aquarium notes: Other Schistura, and indeed other members of the subfamily Nemacheilinae to which it belongs, are all very similar in terms of aquarium requirements and social behaviour

Freshwater Neon Goby
Species traded: Stiphodon atropurpureus
Adult size: Up to 5 cm
Distribution: East Asia, from Japan to the Philippines
Temperature: 20-24˚C
Water chemistry: pH 6-8, hardness 5-20˚dH
Diet: Aufwuchs in the wild but fairly omnivorous in the aquarium taking algae wafers and small frozen foods such as bloodworms
Social behaviour: Males are territorial, but otherwise peaceful
Reproduction: Spawning may occur, but the fry are planktonic in the wild and only develop in seawater
Aquarium notes: Sexually dimorphic, the males developing a vivid blue band along the flanks that gives the species its common name

Giant Danio
Species traded: Devario aequipinnatus
Adult size: 15 cm
Distribution: South Asia
Temperature: 20-25˚C
Water chemistry: pH 6-8, hardness 5-20˚dH
Diet: Will eat most dried and frozen foods, as well as smaller tankmates!
Social behaviour: Hyperactive schooling fish
Reproduction: Typical egg scatterer, breeding is much like other Danio species
Aquarium notes: Other Danio and Devario species are increasingly widely traded, all very similar in terms of aquarium maintenance

Stonelapper
Species traded: Garra spp.
Adult size: Typically 12-15 cm
Distribution: Widely distributed across subtropical and tropical Asia
Temperature: 20-26˚C
Water chemistry: pH 6-8, hardness 5-20˚dH
Diet: Primarily algae and aufwuchs, but also bloodworms, algae wafers, catfish pellets, etc.
Social behaviour: Under aquarium conditions this species is very territorial, though wild fish may form large schools
Reproduction: Not reported in aquaria
Aquarium notes: Various species traded, often difficult to identify but similar in terms of size and maintenance