THE ENDLER'S LIVEBEARER
Text by David Marshall, Editor of The Aquarium Gazette

Background
In 1975 Professor John Endler (a well know scholar of evolution and ecology currently working at the University of California) followed clues from reports of an earlier expedition (Franklyn F. Bond, 1937) to locate two marsh lakes in the Laguna de Patos area of Cumana, northeastern Venezuela, that were home to what was believed to be a beautiful miniature guppy.
Endler
Male & female from Venezuelan Collection

In what is a coastal desert area Professor Endler found these little fish living in brackish waters that had a temperature of 30oC and contained lush growths of microscopic algae. Within a short time he realised that although these fish where guppy look-alikes, they were not another variant of Poecilia reticulata
(guppy) but fellow Poecilia species in their own right. Professor Endler took living specimens to the American Museum of Natural History.
Males from the Guatemalan collection
Image by Robbie Kirkup

It would be a further 30 years before members of the scientific community got around to studying Professor Endler's material and soon noted several small features (mainly the differing structure of the male reproductive organ) that differentiated these little Poecilia from Cumana, from other guppies they had investigated so, in 2005, granted this species the scientific name of Poecilia wingei (Poecilia sub-genus Acanthophacelus).
By this time aquarium fish hobbyists were well ahead in their studies of 'wingei' as the American Museum of Natural History had passed on, with permission, some of their original stock to Dr. Klaus Kallman, who was working at the New York Aquarium, who in turn passed on a number of these little Poecilia to aquarium fish hobbyists in Germany under the name of Endler's (Engler's)
livebearer. As the Reverend John Guppy's name will be forever associated with the common name of the true guppy so, it seems, will Professor Endler's with the common name for wingei.
Not only did the first German hobbyists to work with the Endler's livebearer maintain the true strain of this fish, they also made crossings with a variety of colour strains of Poecilia reticulata.
Finding that the resulting fry from these crosses were quick to grow they expected that, at the adult stage, they would reproduce in commercial numbers but when this did not happen they abandoned this programme.
In the years that followed the popularity of the true strain of Endler's livebearer would fluctuate greatly and throughout the 1990's hobbyists in the U.K., through the interest created by specialist groups such as Viviparous, would do as much as anyone to maintain viable aquarium populations.
With interest in the work of the U.K. groups becoming universal, populations of Endler's were shipped to both Japan and the U.S.A.
Not only did the American hobbyists maintain these fish but sought out new breeding stocks from the Laguna de Patos area. The initial result of this work would find new populations that extended the known natural range for the Endler's livebearer. More populations yielded Endler's with background colour and foreground pigmentation that differed from population to population.
This made viable crosses, and probably crosses with reticulata for new colour strains, a reality that was quickly followed through. An 'Endler's revolution' was thus created, which is now seeing a number of 'new' Endler's strains arriving into the U.K., at a very fast rate, carrying with them all sorts of trade names including tiger, orange spotted, swordtail and peacock tail.
Although I love to see the new strains, for me, nothing can beat the beauty of the fish from Dr. Endler's original collections. Growing to a maximum size of 1.5cm the sleek looking males sport dark green bodies with patches of orange, scarlet and black. The caudal fin has extensions, which should be of equal size, of orange-dark red edged with black. In contrast females, growing to a size of 2cm, are of a plain olive.
There is also another very important point that we must remember. As with many countries that see tourism as a valuable industry, the Venezuelan Government have encouraged the expansion of resort areas in recent years and it is now believed that the marsh lakes from which Dr. Endler's brought home the original strain of wingei have fallen foul to such development. Only through maintaining original populations and their true colour forms may we, one day, play an important part in returning home genetically viable stock (although watered down) to replace those lost in the wild.
Aquarium Care
Although always on the go, Endler's livebearers will live quite happily, and fairly crowded, in aquariums no greater than 45x30x30cm. Small sized gravel forms the substrate while variously sized aquatic plants suffice as the décor. It is important, particularly for the emerging fry that we offer shelter at the water surface and the plastic plants sold for vivariums, held in place by suckers, are useful in this respect. Hard freshwater conditions, with a constant temperature of 25 to 26oC, should be employed. Tonic salt may be beneficial too but is not essential for maintenance of aquarium-bred Endler's. As long as regular water changes are made filtration can be minimal.
Although I recommend that Endler's livebearers are kept on their own, and in a ratio of 3 females to every male to start with, catfish of the genus Aspidoras, make good companions and will leave Endler's of all sizes alone.
As Endler's have very small mouths always crush any flaked food, which should be either a special formulation aimed at guppies or contain a high vegetable content, prior to feeding. What always surprises me, is that of all the small fish species I have kept, this is the one in which microworms are adored from the day of birth to the day of death.
Amazingly, in aquaria, male Endler's soon learn that if they pretend food is heading their way females, who have been keeping a wary distance, will be drawn out of hiding and many 'sneaky' copulations occur in this way.
Although Endler's are not prone to whitespot or velvet disease their lifespan is usually less than a year, as males wear themselves out through the constant chasing of females (and to a lesser extent through feuding with rival males), whereas the rigors of fry birth takes an early toll upon their mates.
Breeding
No special breeding aquarium or conditioning of pairs is needed with Endler's livebearers as when males are not searching for small food particles they spend all of their time courting and trying to mate with available females. Members of the Poecilia family are all oviparous livebearers. Ecologists believe that the superfoetation system of reproduction employed by these fish came about as a result of environmental pressure to produce a large number of fry, not only to ensure a next generation of their kind in the presence of resident predatory water living creatures, but also as a 'fast food source' for a number of migrating bird species. Basically, one mating, with the male employing his modified anal fin (gonopodium) for milt transfer, sees the female store milt in her body that is then used to fertilize several broods of eggs.
Development of the fry takes place within their egg sacs. On average every 28 to 30 days the female delivers broods of fragile fry, which can be as few as 5 in the first brood to extraordinary large numbers at the final (usually 6th) brood, that emerge curled like miniature balls. The fry's need for swimbladder inflation at the water surface often leads to their downfall. Thankfully, not only will the surface plant cover save many fry lives in this respect but of the many Poecilia species I have kept it is adult Endler's which practice the least amount of cannibalism towards their own fry. If your intentions are to produce large numbers of fry then you will require the use of several small aquaria, set-up as above, in order to place a female who is about to give birth, as indicated by the darkening of the anal opening which tells us that the female is 'gravid', as this is the best way of saving the majority of fry born - who can even fall foul of their mother's appetite.
But should you wish to just maintain a colony within the original aquarium, then a separate aquarium(s) is not a necessity, as enough fry, eventually more than you may be able to cope with, will survive.
It is the initial movement of the fry that prompts a 'fast food' response from the adults and the fry that survive this drama usually are left alone and thrive. The fry, which are plain olive in colour, easily feed from birth upon both microworms and brine shrimp. Do not worry if growth appears slow. Proportionally young males, although the first such males to declare their sex are not always the strongest and best for breeding, develop their reproductive capabilities first. Watch their caudal area for the first signs of burgeoning colour.
We owe a big debt to Dr. Endler for bringing such wonderful little fish into the aquarium hobby.