This species is arguably one of the most misunderstood in the hobby since it's wholly unsuitable for smaller aquaria despite its ubiquitous availability.
Most retailers sell it without providing what should be considered essential information regarding long-term care and most specimens undoubtedly fail to reach their potential in captivity. The purchase of a group is also a considerable investment given that if properly cared for typical life span is in excess of twenty years.
Populations from Borneo and Sumatra are documented to exhibit slight differences in patterning, the most obvious being the presence of black colouration in the pelvic fins of Bornean fish, almost completely black in some specimens.
In contrast the fins of Sumatran examples are a uniform reddish colour. The black band on the caudal peduncle also tends to terminate closer to the fin itself in Bornean than Sumatran fish.
A further observation is that in some Bornean individuals the dark bands on the body develop thin, pale borders although we're unsure if this is specific to fish inhabiting a particular river drainage, an artefact of age or something else.
The two populations are thought to have diverged from one another around 9.5 million years ago and 'reintroduction' of specimens from Sumatra to Kalimantan in order to rebuild stocks may have already resulted in hybridisation within the native populations there.
It's now illegal to collect large specimens in Indonesia and annual catches of smaller fish have declined greatly, so native fishermen in some areas have been forced to change their tactics in order to keep trading. Traditionally the most common collection technique involves using lengths of bamboo with openings cut into each segment.
These are normally weighted with stones to make them sink and hung from overhanging or marginal vegetation. The loaches take refuge in these at night and the fishermen return during hours of darkness to collect them.
Smaller specimens of 20 – 80 mm0.8 – 3.1 in have been collected in this way for many years, usually during the month of February, but numbers have fallen away sharply since the turn of the century.
In the Batang Hari river, Sumatra, a different technique now represents the most productive method of collection.
Here C. macracanthus appears to spawn not only in the flooded tributaries but in the plains surrounding the river itself, and local fishermen now collect the pelagic larvae which drift into the main river channel and grow them on to sell to middlemen or larger distributors. Perhaps as many as 10,000,000 specimens are raised and shipped from the area in this way each year.
C. macracanthus was for many years included in the genus Botia, but in 2004 Kottelat moved it into the new genus Chromobotia in order to tidy up a loose end left open by earlier studies, particularly one published by Nalbant (2002).
He had already split four of the putative monophyletic lineages within the family Botiidae into distinct genera but failed to address this species which is clearly different to all other members.
The main distinguishing features useful to aquarists are the unique colour pattern and adult size but it's also identifiable by a combination of characters given as follows by Kottelat (2004): mental lobe developed in a barbel; fronto-parietal fontanelle large and elliptical; anterior chamber of gas bladder partly covered by bony capsule, posterior chamber large; top of supraethmoid very broad; optic foramen rather small; suborbital spine not strongly arched and bifid; head naked.
The family Botiidae has been widely considered a genetically distinct grouping since Nalbant (2002), having previously been considered a subfamily (Botiinae) of the family Cobitidae. Nalbant also moved some previous members of Botia into the new genus Yasuhikotakia based on a number of morphological characters.
Later Kottelat (2004) made further modifications to the taxonomy, raising Chromobotia for B. macracanthus and confirming that species previously included in the genus Hymenophysa should instead be referred to Syncrossus.
The former alteration was based on colour pattern plus some morphological characters and the latter because Hymenophysa not only represents a spelling mistake (McClelland's original spelling was Hymenphysa) but is a junior synonym of Botia.
More recently Kottelat (2012) erected the genus Ambastaia to accommodate A.nigrolineata and A. sidthimunki, two former members of both Botia and Yasuhikotakia.
As a result of these works the family Botiidae is thus divided into two tribes within which Botia appears to be the most basal lineage:
Tribe Leptobotiini - Leptobotia, Parabotia, Sinibotia.
Tribe Botiini - Ambastaia, Botia, Chromobotia, Syncrossus, Yasuhikotakia.
Phylogenetic studies by Tang et al. (2005) and Šlechtová et al. (2006) have largely confirmed this system to be correct although the latter disagreed with the placement of Sinibotia, finding it to be more closely related to the tribe Botiini.
Ambastaia nigrolineata and A. sidthimunki were found to be more closely-related to both Sinibotia and Syncrossus than Yasuhikotakia, despite being considered members of the latter at the time. Šlechtová et al. also proposed the use of subfamily names under the following system:
Subfamily Leptobotiinae - Leptobotia, Parabotia.
Subfamily Botiinae - Botia, Chromobotia, Sinibotia, Syncrossus, Yasuhikotakia.
Within these Botia appears to be the basal, i.e., most ancient, lineage and in a more-detailed phylogenetic analysis Šlechtová et al. (2007) confirmed the validity of the family Botiidae with the genera listed above as members rather then being grouped into subfamilies. This more recent, simpler system is the one we currently follow here on SF.
Some behavioural routines exhibited by botiid spp. have been recorded often enough that they've been assigned non-scientific terms for ease of reference.
For example during dominance battles (these occur most frequently when the fish have been introduced to a new tank, or new individuals added to an existing group) the protagonists normally lose much of their body patterning and colouration, a phenomenon that's come to be known as 'greying out'.
Such displays will sometimes also happen within an established group as individuals seek to improve social ranking but are usually nothing to worry about.
Interestingly some observations suggest that the character of the highest-ranked, or alpha, fish appears to affect that of the whole group though it must be said that scientific studies of botiid loach behaviour are virtually non-existent.
It certainly seems that they display a degree of 'personality' with some specimens being naturally bolder or more aggressive than others, for example. The alpha is normally the largest specimen within the group and often female.
'Shadowing' is an interesting behaviour in which younger individuals swim flank-to-flank with older, mimicking their every movement. Some keepers report that more than one smaller fish may shadow a larger simultaneously, with even three or four on each side!
The reason for it is unknown; it may relate to a group staying in touch with one another when rivers swell during times of flooding, perhaps reducing drag by swimming 'in formation' or having some other communicative function.
It's been observed in aquaria with both high and low water flow and seems to be habitual to the extent whereby some individuals will shadow other fishes if no conspecifics are present.
Sound also appears to be an important factor in communication since these loaches are able to produce audible clicking sounds, these increasing in volume when the fish are excited. The behavioural aspects of this phenomenon remain largely unstudied but the sounds are thought to be produced by grinding of the pharyngeal (throat) teeth or subocular spines.
A further curiosity is the so-called 'loachy dance' which involves an entire group swimming in a constant, restless fashion around the sides of the tank, usually utilising the full length and height.
The reasons for this are unknown and reports as to when it occurs vary but the most common triggers appear to be the addition of food, fresh water or new conspecifics, and it can last anything from a few minutes to a day or more.
Botiids also often settle at peculiar angles, wedged vertically or sideways between items of décor, or even lying flat on the substrate. This is no cause for alarm and appears to be a natural resting behaviour.
C. macracanthus also possesses sharp, motile, sub-ocular spines which are normally concealed within a pouch of skin but erected when an individual is stressed, e.g., if removed from the water. Care is therefore necessary as these can become entangled in aquarium nets and those of larger specimens can break human skin.
Botiids are also susceptible to a condition commonly referred to as 'skinny disease' and characterised by a loss of weight. This is especially common in newly-imported specimens and is thought to be caused by a species of the flagellate genus Spironucleus.
It's treatable although the recommended medication varies depending on country. Hobbyists in the UK tend to use the antibiotic Levamisole and those in the United States Fenbendazole (aka Panacur).
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