We still know very lit­tle about the mys­te­ri­ous Crys­tal rain­bow te­tra. What we do know is that it’s stun­ning as a stained glass win­dow.

Practical Fishkeeping (UK) - - Contents - WORDS: Steve baker

The Crys­tal rain­bow te­tra is still some­thing of a mys­tery to science, but it’s pretty as a stained glass win­dow.

It’s of­ten said that, as hu­mans, we know more about space than we do about the oceans on the planet we in­habit. In re­al­ity that’s prob­a­bly not strictly true; we don’t even know the size of the cos­mos, let alone what might ex­ist within it.

But it con­tin­ues to sur­prise me how lit­tle we know of what’s much closer to the sur­face, and this bonny lit­tle te­tra is one crea­ture we know of, but still know very lit­tle about.

I look at this fish and think of a stained glass win­dow, but in terms of a com­mon name, Trochilocharax

or­na­tus caught on as the Crys­tal rain­bow te­tra, orange-tailed glass te­tra, or the Hum­ming­bird te­tra, de­pend­ing on who you talk to. Be­ware of re­search­ing by that last com­mon name though, as

Characid­ium fas­cia­tum, the Darter te­tra, is also some­times called the Hum­ming­bird te­tra, and it’s a very dif­fer­ent fish.

T. or­na­tus was first bought to the at­ten­tion of ichthy­ol­o­gists when it was shipped from Peru in 2003 by Ger­man im­porters Aquar­ium Glaser. It was orig­i­nally con­sid­ered to be of the Hete­rocharax genus, be­fore be­ing de­scribed to science by Zarske in 2010. Zarske opened a new genus,

Trichilocharax, and tribe, trochilocharacini, for the Crys­tal rain­bow te­tra due to rather in­di­vid­ual-look­ing den­ti­tion and some hooked fin rays that re­late to no other characin – to this day we know of no closely re­lated te­tra.

other than just ‘Peru’, sci­en­tists aren’t sure about the dis­tri­bu­tion. the spec­i­mens used by Zarske to de­scribe the species came from an im­ported group, and while they know the im­port came from Iquitos, they don’t know where the fish were caught, or from what kind of habi­tat.

It’s widely be­lieved T. or­na­tus hails from small black­wa­ter streams with lit­tle flow, low con­duc­tiv­ity and neg­li­gi­ble hard­ness, and it does well in these kind of con­di­tions in aquaria. there’s some thought that their true dis­tri­bu­tion lies in the Rio nanay basin, though pre­ferred wa­ter con­di­tions would be near iden­ti­cal to those men­tioned.

the new tribe is placed in the sub­fam­ily ste­vardi­inae, a group of over 300 species of Cen­tral and south Amer­i­can tetras with many mem­bers that adopt an in­ter­nal in­sem­i­na­tion strat­egy. It’s be­lieved that the Crys­tal rain­bow te­tra does that too.

In the tank, this diminu­tive del­i­cacy (1.7cm max­i­mum) dis­plays stun­ning colours un­der full­spec­trum light­ing, with blues and greens re­flected in their bod­ies, and males dis­play­ing beau­ti­ful burnt or­anges and yel­lows in their finnage.

sexes are easy to dis­tin­guish, with males har­bour­ing longer, more colour­ful fins, es­pe­cially the dor­sal and pelvic fins, while fe­males de­velop a slightly more rounded body.

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