Livebearers don’t have to be gaudy, line-bred crowd pleasers. New contributor Hannah Taylor waxes lyrical about a subtle beauty with a delightfully dark streak.
IF TASKED WITH coming up with a brackish livebearer, the average aquarist would be forgiven for thinking the options are limited to the common molly, Poecilia sphenops, or their congeners, the sailfin and giant sailfin mollies, respectively Poecilia velifera and P. latipinna. I know I did when planning the stocking for my first brackish system, but didn't feel my tank—at just over 60cm—was large enough for the latter two, and I wanted something less common than the aquarium strains of poecilids that are the bread and butter of LFS everywhere.
Enter Girardinus metallicus.
Never heard of it? No surprise; unlike the arguably freakish, garish guppies, 'endlers', and swordtails mass-produced in Asian farms for shops, Girardinus lack the admittedly remarkable, bright colours and diversity of form of these community staples. It is this which, I believe, has led to their being so frequently overlooked when stocking the brackish tank.
Love for livebearers
As community fish, poecilids—the family that encompasses the common livebearers—undoubtedly have much to commend them: they're hardy, easy-going, attractive, and for those so inclined, easy to breed.
G. metallicus shares many of these traits but wears a more muted garb than either common guppies or mollies. Nonetheless, their livery of metallic gold and silver is indisputably attractive, though this subtle beauty would not be shown off to best effect under the bright LEDs of many shop systems.
Most striking is the jet-black underside the males develop when they reach maturity, stretching from below their mouths (hence the colloquial moniker 'black chin livebearer') to the ends of their gonopodiums (the modified anal fins that, in viviparous fishes, function like dart guns for injecting sperm into females).
The reason for this eye-catching feature on what is otherwise a plain fish, whose markings pale next to the neon hues of many others, was unknown for many years. However, 2014 and 2015 studies into piscine courtship behaviour found that the extent of black colouration positively correlated with dominance in males: put simply, the blacker a black-chin's chin, the higher up the social ladder in the shoal he is, and therefore the more likely to mate. Over generations, this has led to positive selection for the black-chin trait amongst wild populations, so it is now almost universal. It has also been suggested that the g
