HOW FLOW CAN YOU GO?
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.
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.
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.
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.