Chromobotia macracanthus, the Clown Loach

Chromobotia macracanthus (Clown Loach), formerly Botia macrantha. "Macracanthus" (its new name is declared to be masculine, just to keep us on our toes) refers to the big spine by the eye, no bigger than you'd expect, though, and perfectly in proportion to this giant among Botias, who slowly reaches 12 inches in a roomy aquarium, and apparently gets to 15 inches in the wild. Maurice Kottelat separated this species from Botia in 2004, based on a number of unique morphological features, only one of which is the comparatively giant size it attains, even in captivity. 
Sexing them is fraught with ambivalence. I've heard several times that males have a longer tail fin with a more pronounced fork, but since they scarcely ever breed in aquaria and take years to reach sexual maturity, only dissection would confirm this. Singapore sources tell one that the Sumatran specimens generally have a silvery sheen over the body; whereas the Kalimantan (Borneo) specimens have a more intense reddish coloration. This could be due to the habitat. The Sumatran specimens inhabit murky water rivers emptying northeastwards, like the Batanghari in Jambi Province, whereas the South and West Kalimantan ones prefer brown water rivers like the Barito or even blackwater tributaries. Chromobotia macracanthus is one of the fishes found in the seasonally flooded Lake Sentarum, in the last large vestige of a lowland peat swamp habitat remaining in Borneo. The dissolved tannins and humic acids in black water tend to accentuate their reddish colours, according to a University of Singapore report. I would also think that paler Clown Loaches might be more obvious to predators in the dark waters. And I find Botia colors fade or darken according to their general health and stress level.
Clown Loaches are the easiest Botia to come by. Though they are tentatively being pond-cultured in Thailand, the wild-caught populations from central Sumatra and southern and eastern Kalimantan (Borneo) are still cheaper; they are the outstanding tropical fish export of Indonesia, according to an Indonesian report of September 2011. They are only seasonally available; the price fluctuates severely: sometimes late summer finds the best bargains. I prefer the brighter red and more golden Borneo Clown Loaches. When I'm looking for a Clown Loach, I select it for strong orange-gold body color and bright red fins, and for deep velvety black banding. I avoid individuals with pinched bellies, for Clown Loaches very often carry Camallanus intestinal nematodes. I also make sure the black bands are in the correct classic configuration, with the front edge of the main body band continuing uninterrupted onto the dorsal fin. Sometimes the genetic information gets scrambled and the pattern suffers. Some people actually look for these misfits; like a six-toed cat, I suppose.
Clown Loaches are the least furtive of the Botiin tribe, which includes BotiaChromobotiaSyncrossusYasuhikotakia. They're day-active and sociable by nature and seem to be more secure in one another's company: sufficient reason to keep them in groups of three or more. Match your community for size, because these loaches maintain a pecking order and the littlest clown may be picked on. Often it's noticed that in a small swarm of Clown Loaches, one or two will grow noticeably faster than the others. This might just be successful competition for food, but the fishes really don't seem that aggressive towards one another. Some fishkeepers think it's a question of growth suppressant hormones diffused into the water, but no scientist has been able to isolate such a hormone. I think it's just a matter of time before the hormone is found.
The National University of Singapore maintains at its website an account of wild Clown Loach collecting that is very illuminating. Juveniles are found in abundance in the large rivers of central Sumatra and central Kalimantan Province during the high water seasons. The adults breed at the beginning of the high water season and locals catch the young soon after. At other times of year, the individuals are too dispersed or too large to be of value to the trade. The size range preferred by aquarists being three to eight centimeters, smaller fishes are held in grow-out pools, where growth is more rapid than anything we ever see in aquaria. Some exporters also keep excess stock to sell later at higher prices when the fish is not in plentiful supply. Size is important in the export aquarium trade. According to the University of Singapore, larger specimens (adults can attain sizes up to 40 centimeters, equivalent to 15 3/4 inches) tend to be more carnivorous and do not fit in well in community tanks. Most individuals are caught at two to four centimeters size as they come downstream from their breeding grounds upriver. About 20 million C. macracanthus are exported from Indonesia through Singapore yearly, but the fishes caught are all juveniles, and breeding populations are left intact. So it looks as though the practice is sustainable. The breeding grounds are not yet precisely known. Indonesia has imposed a ban on the export of specimens larger than 10 cm in length to protect breeding adults, but also quite consciously to impede captive breeding programs.
The collecting techniques are interesting. In Sumatra, local collectors catch Chromobotia macracanthus in bamboo poles stuck every meter or so into the river bank. The poles have previously been drilled just below the nodes of the bamboo to provide holes adjusted to the size of the fishes that are to be attracted. At regular intervals during the peak season, the collector will lift out each pole in turn and empty the resident fishes into containers or dump them directly into water filling the boat's bottom. Later, the catch will be sorted and transferred into holding tanks, before sale to a middleman. In Kalimantan, in a variation of the technique, a bundle of trimmed and split bamboo poles are tied together, secured to the riverbank and sunk with stones. Fish take refuge in and among the bamboo poles. The collector lifts up the whole bundle and shakes out the refugees into a container. This technique is somewhat more stressful to the fish.
In the more inaccessible central Kalimantan, the exploitation of C. macracanthus is not as intense and the locals catch adults for food. Bumi Bormeo in Sampit markets live B. macracantha among its food products.
Captive artificial breeding of Chromobotia macracanthus is possible and is infrequently described; Martin Thoene summarized on-line of foot-long Clown Loaches in an account originally published in Practical Fishkeeping. It does take quite a while for Clown Loaches to reach sexual maturity. The spawning loaches of a British fishkeeper were eighteen years old! Commercial breeding has been accomplished in Thailand; however, it is still not cost effective, as the wild-caught stock is still much cheaper. The species has some unusual breeding characteristics. Captive breeding technology might be developed to be commercially viable, in order to take pressure off wild stocks. The National University  of Singapore encourages the trade to have "foresight to counter the inevitable extirpation of wild stocks." ("Inevitable" suggests an unpromising official fatalism, doesn't it?) If the technology has not been developed in advance, the University warns, then the whole species may face extermination due to unscrupulous fishing methods, and, more worrying, habitat destruction. I condensed this material from the website of the National University of Singapore's  article "Freshwater Fishes of Southeast Asia: potential for the aquarium fish trade and conservation issues." 
Links. Ola Åhlander has posted an outstanding illustrated article on Chromobotia macracanthus in the wild and in the aquarium. 
There is a brief article that covers care and the renaming of C. macracanthus at SeriouslyFish.
Audra Calvin's detailed introduction to making Clown loaches comfortable in the aquarium is at FishProfiles.