We all have ideas of how to set up a flow­ing stream tank, but how does a pro­fes­sional re­searcher go about it? We asked one, and this is what he told us.

Practical Fishkeeping (UK) - - Contents -

How a pro­fes­sional re­search sci­en­tist goes about set­ting up a flow­ing stream tank for ag­ile hill­stream loaches.

HILL­STREAM LOACHES are small fresh­wa­ter species found in the fast-flow­ing streams of Asian trop­i­cal rain­forests. In the wild, they glide over smooth rocks in strong cur­rents and climb ver­ti­cal, even over­hang­ing sur­faces with ease.

Un­der­stand­ing how these tiny fish cope with such ex­treme en­vi­ron­ments might lead to sig­nif­i­cant break­throughs in fluid dy­nam­ics, per­haps al­low­ing us to re­duce the drag on ships, or re­duce the cost of pump­ing wa­ter.

Hill­stream loaches have unique scale struc­tures and body shapes, and it may be these adap­ta­tions that give them the abil­ity to fight the cur­rent with­out ex­pend­ing sig­nif­i­cant amounts of en­ergy.

As re­searchers, our ex­per­i­ments are only worth do­ing if the fish we keep in the lab are healthy and be­have as they do in the wild. We have spent sev­eral years im­prov­ing our aquar­i­ums to match the eco­types the hill­stream loaches pre­fer. To that end we went to Bor­neo to see them in the wild.

Loaches in Bor­neo

Hill­stream loaches come from rain­for­est moun­tain streams. It rains a lot. Sur­pris­ingly there’s of­ten only a thin layer of soil over be­drock or clay, so rain reaches the streams quickly. A river, nor­mally a trickle, turns into a tor­rent in a few hours, or even min­utes. Leaves, twigs, silt, gelati­nous al­gae, and any­thing else that can’t get out of the way, is

swept down on a tor­rent the colour of milky cof­fee. A cou­ple of hours later, the clouds clear and the sun reap­pears; four or five hours later. the sed­i­ment drops out and the wa­ter clears. This cy­cle is re­peated ev­ery cou­ple of days to ev­ery few weeks, de­pend­ing on the sea­son.

Peo­ple in Bor­neo eat these fish, known as ‘rokot’, but it’s quite a trek to the high moun­tain streams, so they aren’t eaten of­ten. Many peo­ple we met had fond mem­o­ries of catch­ing them as chil­dren and were keen to ad­vise. One in­di­ca­tor was a cer­tain aquatic snail: “Where there are snails there are rokot.” It was true and use­ful as the fish could be dif­fi­cult to spot.

We were look­ing at meth­ods for sampling the fish in the fu­ture with­out harm­ing them, so we cap­tured a few with hand-nets and pho­tographed them be­fore re­turn­ing them all to the rivers.

The tank

To keep hill­stream loaches happy, your tank should have some spe­cific fea­tures: fast flow­ing wa­ter to al­low al­gae to grow in strong light­ing, darker pro­tected ar­eas with slower flow and even a few ar­eas with lit­tle or no flow. Vari­a­tion is the key.

Like a tiny Adam Peaty, hill­stream loaches prob­a­bly need reg­u­lar work­outs to stay in top form, not only to help main­tain mus­cles and over­all fit­ness, but also per­haps to keep them men­tally ac­tive. Maybe they even get bored, wor­ried or stressed in calm wa­ter.

Achiev­ing flow rates com­pa­ra­ble to those found in the wild is tricky. Ide­ally, wa­ter should be mov­ing about 1-2m per sec­ond. A typ­i­cal high-power pump like an Eheim com­pact+ 5000 moves wa­ter at about half a me­tre per sec­ond and this quickly drops off only a few inches from the pump out­let. If you were aim­ing for a cur­rent of 2m per sec­ond through­out a 120 l tank, you’d have to shift the en­tire 120 l twice a sec­ond. That’s some aquar­ium pump – 900,000 litres per hour!

There is an eas­ier way to get fast-flow­ing wa­ter though – keep some ar­eas of the aquar­ium shal­low.

What we saw in Bor­neo has been ap­plied to our tank de­sign and hus­bandry. Wa­ter is pumped to a shal­low plat­form, then flows over rocks and falls back into the main tank via a ramp or over a wa­ter­fall.

In the wild, when the stream floods, loaches climb, rather than shel­ter

We used two Eheim com­pact+ 5000 pumps at full speed in a 100 l tank through sponges on strain­ers to move the wa­ter from the main tank to the plat­form. A rich layer of al­gae grows on the rocks in the strong light. The wa­ter­fall oxy­genates the wa­ter and pro­vides con­stant sound too; the ramp pro­vides ac­cess and an in­ter­est­ing vari­able flow fea­ture. We use ‘off­line’ fil­ters, and en­cour­age shrimps, snails and al­gae to

share the tank. There’s no sub­strate, just large rocks and bog­wood. The tank has both fall­ing wa­ter and ar­eas with mod­er­ate to low flow.

In the wild, when the stream floods, loaches climb, rather than shel­ter. This time may be the equiv­a­lent of the Olympic fi­nal for these minia­ture Adam Peatys. The deeper wa­ter may al­low them to get over ob­jects that would be bar­ri­ers in shal­lower wa­ter, and may also be where they can more eas­ily evade preda­tors like

Clar­ias cat­fish. Cat­fish use suc­tion to

catch prey and so the loaches’ abil­ity to re­main at­tached with­out sub­stan­tial mus­cu­lar ef­fort may be a ben­e­fit in a sur­prise at­tack.

This be­hav­iour in stream flood­ing is sub­tly im­por­tant as it means the loaches aren’t chal­leng­ing their phys­i­cal lim­its all the time. Re­lax­ation, rest and so­cial ac­tiv­i­ties are all parts of en­sur­ing peak per­for­mance when nec­es­sary. Of­ten, we found them in calm, clear pools, with­out ex­ces­sive flow – 0.2-0.4 m/s. Here they would graze and share space with shrimps, other fish and snails; nat­u­rally in­quis­i­tive but al­ways near shad­ows, and fast-flow­ing and fall­ing wa­ter – ever vigilant. Our tanks are de­signed to mimic these vari­able con­di­tions in shel­ter, light­ing and flow.

We also use ‘off­line’ liv­ing fil­ters – tanks con­nected to the main tank via smaller pumps. The re­turn wa­ter is piped onto the up­per plat­form of the main tanks, of­ten through a spray bar, to add to the flow. These smaller tanks con­tain fil­ter sponges, Anu­bias, shrimp, snails and fish such as Dan­ios. We also put peat, Cat­appa leaves, Alder cones and bog­wood in here. We feed the Dan­ios flake and some cir­cu­lates through the main tank. These tanks pro­vide a range of fil­ter­ing and ni­tro­gen cy­cling ser­vices that help ‘feed’ the main tank. The idea is that they act like an up­stream sec­tion of nat­u­ral river, adding smells and nu­tri­tion in the same way.

Wa­ter pa­ram­e­ters

The book ‘The Bor­neo Suck­ers’ by Dr Tan Heok Hui pro­vides a good idea of what hill­stream loaches from Bor­neo are used to. From Dr Tan’s field notes, the av­er­age ph of the wa­ter is 7.5, with records from 6.0 to 8.7. There’s no sim­i­lar book for the Sewellia but­ter­fly loaches of Viet­nam, but there is a great sci­en­tific pa­per for Sino­gas­tromy­zon pulien­sis, a sim­i­lar species found only in Tai­wan. Shyi-liang Yu and Teh-wang Lee sam­pled fish in over 60 river sites. Av­er­age ph was 8.2 (range 6.2-10.9), av­er­age tem­per­a­ture 23°C (range 18-30°C), av­er­age flow 0.9 m/s (range 0.12-2.32). These av­er­age pa­ram­e­ters are a good place to start. We al­ways aim for them – also with car­bon­ate hard­ness over 7° kh, which pulls the ph up to roughly 8.0.

As a rule, we don’t mea­sure ph or GH, but mon­i­tor and main­tain KH around 8-10 units. We tested the wa­ter in Bor­neo with stan­dard test kits (API liq­uid test kit KH, GH, and ph) and con­firmed these av­er­age fig­ures were ac­cu­rate for five of the lo­ca­tions where we found fish.


While hill­stream loaches will eat stan­dard fish flakes, we’ve found

Where there are snails, there are rokot

they need to eat al­gae for long-term health. We use Repashy Soilent Green gel as a sup­ple­ment to en­sure they al­ways have ac­cess to a well-bal­anced diet.

There are many types of al­gae, of course, and some only grow in fast flow. Af­ter rocks have been grazed by adult hill­stream loaches for a few months, they de­velop a dark, red­black al­gal layer full of bac­te­ria, crus­taceans, di­atoms, and other food, such as snail and shrimp eggs.

Gelati­nous al­gae can be a sign that there’s too lit­tle flow in the tank. It’s not toxic to the fish, it just stops them get­ting at the stuff they like.


Be­cause these fish are used to change in their nat­u­ral rivers, they don’t mind a big wa­ter dis­rup­tion. We clean the tanks weekly by re­mov­ing all the rocks and wood – ev­ery­thing out but the fish! So all the rocks in the main tank are rinsed in tank wa­ter and repo­si­tioned, with a 40-50% wa­ter change. The chang­ing pat­tern of rocks and caves, in a fa­mil­iar pat­tern of flow, is a fur­ther stim­u­lant to the fish, sim­i­lar to their nat­u­ral habi­tat, and al­lows them to ex­plore and re-es­tab­lish favourite places and routes. We of­ten find small fry in the changed wa­ter and move these to a sep­a­rate tank for ju­ve­niles. Oc­ca­sion­ally we roughly scrape the rocks with an old knife – the fish seem es­pe­cially keen to graze them af­ter.

The be­hav­iour we ob­serve in our aquar­i­ums is sim­i­lar to what we saw in the wild. Like many loaches, hill­streams like to hide, es­pe­cially from peo­ple, and we en­sure they have ad­e­quate places to do so. They’re nat­u­rally in­quis­i­tive and so­cial fish; while they may hide when we en­ter the room, they re-emerge af­ter only a few min­utes. All sizes play­fully spar with sim­i­lar-sized fish and they ap­pear re­laxed as they ex­plore their tank.

One good test of health is breed­ing and we’re pleased to say some of our fish more or less breed con­tin­u­ally.

ABOVE: We could learn a lot about hy­dro­dy­nam­ics from hill­stream loaches.

BE­LOW:Sewellia ‘SW01’ and ‘SW02’.

BE­LOW: When flow drops, wa­ter set­tles and clears.

Right: this set-up of­fers dif­fer­ent en­vi­ron­ments to repli­cate na­ture’s va­ri­ety.

ABOVE & BE­LOW: Flow rates fluc­tu­ate mas­sively in the for­est streams of Bor­neo.

Not just al­gae, hill­stream loaches need the right al­gae.

Repashy’s al­gae paste food goes down well.

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