For some reason, I like small fish. The tinier the better. It's not just the practical reason that such minute creatures can be easily housed in modest accommodation. Their very existence, indeed the very plausibility of their survival in the wild, seems amazing to me. The microcyprinids in the genus Boraras, which reach barely a couple of centimetres) are distributed throughout suitable habitats in Southeast Asia, with B. micros, B. uropthalmoides and a couple of undescribed species native to Thailand and the Mekong basin in Indochina, B. merah and B. brigittae to Borneo, and B. maculatus to the Malayan Peninsula, Singapore and Sumatra.
There appears to be two distinct tribes within this genus: one comprising species with a slimmer profile (B. brigittae, B. merah, B. maculatus, B. micros) and the other having members with a much stubbier body (B. uropthalmoides and the undescribed Thai species). Brittan (Rasboras: Keeping & Breeding Them in Captivity, T.F.H. 1984) suggests that B. micros, which is found only in two widely separated marsh pools in northern Thailand, is a relic of an ancestral-type to the genus. I personally see something akin to B. maculatus as the more likely progenitor to the two species endemic to Borneo.
The fishes are so minuscule that one wonders how they manage to colonise new habitats. They are not strong swimmers, preferring small, shallow pools and streams that lie in the shade of peat swamp vegetation. Perhaps there is a role played by the region's seasonal upheavals such as the monsoons that thunder every winter and burst the banks of rivers to form a wide and wet expanse that links unconnected waterways and peaty depressions that would otherwise be isolated for much of the year. Carried about via the temporal currents, a new generation of fish might find their way (perhaps with the aid of biochemical signals) to suitably sheltered homes, and in a not-too distant time when the seas were lower, these migrations would have carried the tiny fish from their pools of origin all the way across the Sunda shelf to the highlands that are now known as Borneo and Sumatra.
The favoured waters of Boraras are highly acidic and have very low conductivity, with a poor diversity of insect fauna and relatively few aquatic plants save members of the genera Cryptocoryne (Araceae) and Barclaya (Nymphaeceae). They share these waters with many other small fish: the so-called wine bettas in the Betta coccina group, which are slender and tiny members of the genus (Betta persephone barely exceeds an inch) that dwell in semi-permanent peat swamps (in the dry season, the water retreats into subterranean pools and the fish await the rain in these tiny underground puddles); bettas in the B. waseri group; liquorice gouramis in the genus Parosphromenus; chocolate gouramis (genus Sphaerichthys); members of the allied cyprinid genera Rasbora and Trigonostigma (particularly T. heteromorpha, R. pauciperforata and R. kalochroma); and lesser known finned fauna such as small catfish, loaches and gobies.
Boraras brigittae is to many the most spectacular member of the tribe, with a body of glowing scarlet and fins tipped with rubies. Some populations of B. maculatus match it in brilliance, but I am happy to regard both fishes as jewels deserving equal esteem. The popular trade name for this species is mosquito rasbora, probably on account of its sheer size, rather than its colouration. The moniker is to me unseemly, but is arguably better than the hypothetical and more vividly accurate blood rasbora.
Boraras merah is a more subtly coloured species, but as its name indicates (merah is Malay for red), the fish can reach an intensity (scroll down in the linked page) that dazzles, when kept in suitably low pH waters.
Boraras uropthalmoides is popularly known as the exclamation point rasbora for the interrupted dark lateral stripe which tapers off as it approaches the caudal peduncle and reappears as a black spot at he base of the tail. A secondary stripe in vivid orangey red lies above the dark stripe. Unlike his cousins in the same small tank, this little fellow refused to stay still for more than a second, and so the picture above was the best I could get out of an impromptu 5 minute shooting session (I was also too lazy to set up my tripod).
I would also like to show a picture of one of my pygmy gouramis (Trichopsis pumilus), which lives in a tank of green water on the console behind my computer chair. They have been croaking quite a bit lately, uttering small, sharp scratching sounds like frogs singing in falsetto. Sadly, none of the pictures I could take showed up their beautiful baby blue eyes.
Finally, this is one of three wagtail platies (Xiphophorus maculatus var.) born in the same tank that houses the pygmy gouramis. They are just over an inch long now, and their mother has long shifted to the big fish tank
down in the longkang up in the sky. This variety of platy (which is named after the La Plata river in Mexico) has a solid colour body with black tinged fins and black lips. As far as fish go, there are few as perky as my duck a platy. The green tinge of the photo stems from the abundant green spot algae on the tank wall which has not seen an algae scraper (actually, my old credit cards) for about a year.