NEON RED SUNDADANIO
Scientific name: Sundadanio retiarius
Pronunciation: Sun-da-dan-ee-oh ret-ee-arr-ee-uss
Size: To 1.9cm
Origin: Central Kalimantan
Habitat: Peat swamps and slow blackwater streams
Tank size: 40x20x20cm
Water requirements: Very soft, very acidic water; 4.0-6.5pH,
0-4°H
Temperature: 24-26°C
Temperament: Peaceful, active, a little
nervous
Feeding: Tiny flakes and live foods, including Cyclops, micro worm and freshly hatched Brine shrimp
Availability and cost: Used to be marketed as the ‘Red axelrodi rasbora’ but one of the more common species seen on sale. Prices from around £3.50 each
if you like, and they will love you for it. Hardness should never creep above 4°H, and ideally be as little as 1°H. 25°C water temperature is okay, but try not to go more than 1°C either side of this.
RO water or rainwater is the way forward, the latter treated with carbon before use. To acidify it, you want humic and tannic acids, so alder cones and leaf litter are the quick fix. It would be worth getting a job lot of alder cones and sticking 30 or so in a 2-litre bottle filled with RO. Let the cones steep for a couple of weeks and you should be left with a rich tannic cordial that you can add to the aquarium as needed. Aquascapers might be thinking that heavy dosing with CO2 will create suitably acidic conditions, but Sundadanio tend not to thrive in clear water, regardless the acidity.
With such acidity comes a concern for biological filtering. At such a low pH, and with such reduced hardness in the water, the bacteria and archaea we rely on to keep our tanks clean are unable to function. But given the interplay of ammonia and pH (with increasing acidity, decreasing amounts of harmful
‘free’ ammonia are present in the water) that’s not the end of the
Earth as long as things stay acidic. Any tank you set up might as well be a biotope, given that Sundadanio struggle in the community setting, and given that most other community choices won’t tolerate the extreme conditions required by these tiny acidophiles.
There are conflicting reports about the extent of their shyness, with some aquarists suggesting that Sundadanio will hide away from anything larger than themselves, but equally there are tales of reckless abandon in the presence of even Gourami-sized fishes.
A biotope is easy. Opt for a dark, fine and sandy substrate (be careful to acquire sand without anything that might harden your water) and recreate the looks of the natural habitat with heaps of dried leaves and branches. Disregard plants if you’re going for an authentic layout, but do keep the tank well shaded. Go for woefully undersized lamps, or LED devices that you can turn down to minimal output.
For a biotope correct tankmate, if you’re feeling brave than you can seek out some of the sympatric Paedocypris that Sundadanio live alongside (and are closely related to). Paedocypris are the smallest freshwater fish in the world with one species — P. progenetica — reaching just over 1cm (10.3mm to be exact) when fully grown. Just note that if you’re going down this path it would be wise to get a lot of cultures of tiny live foods on the go.
If you’re not feeling that challenge, then you can go for a geographically incorrect Sundadanio/Trigonostigma collaboration. The Harlequin rasbora, T. heteromorpha, or one of its smaller cousins would flourish in the acidic water conditions — far more so than in the everyday community tanks where most end up, in fact.
So, here’s the best bit. You only need the tiniest of aquaria for a Sundadanio set-up. At around 2cm fully grown, you don’t need a big footprint to keep a shoal of them happy. Ever seen those little 16x8x8in tanks on the shelves of your local shop? They’d be perfect. Get a little air-powered foam filter in there and carry out a 20% water change each week, and you could easily house a shoal of eight
Sundadanio on a shoestring budget. I’d probably avoid an internal canister filter as I’ve seen all too many tiny fish get sucked into them or stuck behind them.
Breeding
Captive spawning of Sundadanio is staggeringly rare, but it does happen. To facilitate it, the few breeders who have had success always rely on softer and more acidic water than is readily available to the lay aquarist. Access to RO is a must, and that RO must be of exceptional high quality. General hardness needs to be somewhere between 0-1°H, and carbonate hardness needs to be the same. Over 1°H? Forget about it. The temperature should be a consistent 25°C, while the water wants to be strongly acidic, just as it should be for their regular maintenance. 5.5pH seems to be the right ballpark for spawning. A tank with plenty of tangles of bogwood (ideally the kind that leaches out those lovely dark, discolouring tannins that most community fishkeepers hate) along with lashings of Java moss and a good sprinkling of leaf litter (ideally on the turn and not the fresh stuff) will create a habitat conducive to a little friskiness, and as long as the fish are well conditioned with plenty of tiny live foods then spawning should happen sporadically in this set-up.
Given the adults are so small, you’d be right to expect the tiniest of fry. These spend much of their time out of the way of the parents by lurking down amongst the moss and in the shadows of wood, but if accounts are to be believed the parents aren’t overly eager to consume their offspring — adults and fry can be kept together safely enough.
The smallest of fry foods will be needed, although your decaying leaf litter should also produce a bounty of microorganisms to get the young
off to a good start. Paramecium, rotifers and liquid foods like Interpet’s Liquifry (which has as much utility in feeding microorganisms as it does as a direct source of food) can all be supplied and will be accepted. Importantly, lighting needs to be minimal when attempting any Sundadanio spawn — reports state that they simply will not perform under bright lighting. That being the case, keep an eye on your Java moss. If it starts to die off under the low illumination, either keep swapping it out for fresh or have a look for some synthetic substitute. Good luck!