Livebearers—More than Just the “Big Four” (Full Article)Author: Mike Hellweg
Some, such as the wild-type guppy, are so hardy and prolific that they are even used as feeders for larger, predatory fish. Guppies are found the world over, as they have been used to control mosquitoes in nearly every nation on earth. If that’s not hardy and adaptable, I don’t know what is!
The Retail Big Four
At that time, species were not looked at in the same way they are today. Many of what we now know as separate species were considered just variants of the same species. Swordtails, variatus, and platies (or moonfish, as they were known back then) were crossed to impart different colors and patterns into the various body forms. Two or three different species of mollies were crossed to fix the solid, velvety black coloration we now see in the black molly. Guppies, too, may be crosses of various small species of Poecilia. So instead of calling fancy swordtails Xiphophorus hellerii, it is more correct to call them Xiphophorus sp. domestic swordtail, as they are hybrids of at least three species. The same goes for platies (X. sp. domestic platy) and mollies (Poecilia sp. domestic molly). Guppies are still considered to be a highly variable species, P. reticulata, but in the future, that may change. Two new species (P. wingei and P. obscura) were described in the past decade from what had long been considered just locations of P. reticulata, so who knows what the future may bring?
What Are Livebearers?
Livebearers provide no further brood care after release, and many of them will even prey upon their progeny right after birth, so hobbyists often have to devise ways of separating parents and fry. Contrary to the popular myth that females simply carry the eggs around until they hatch and then release fully formed fry, almost all livebearers provide at least some nourishment to the developing embryos. Various studies over the years have shown that the fertilized eggs cannot develop into viable young outside of the womb.
This can vary greatly from simple gas exchange for those fish, whose embryos actually lose weight as they develop (lecithrotrophs), to those that provide nourishment via a sort of umbilical cord and placenta (matrotrophs), to those that go so far as to provide unfertilized eggs for the developing embryos to eat (oophagy) in the womb, some of which (e.g., Nomorhamphus ebrardtii) might even consume some of their developing siblings.
By far the best-known group of livebearers is the family Poeciliidae. The retail big four were all developed from members of this family, but there are many other species popular in the hobby that are available from other hobbyists via aquarium clubs, national clubs, and internet auctions. At recent club auctions, I’ve seen members of the genera Xiphophorus (wild-type swordtails and platies), Poecilia (wild-type mollies and guppies), Limia (molly relatives from the Caribbean Islands), Alfaro, Belonesox, Brachyrhaphis, Carlhubbsia, Girardinus, Gambusia, Heterandria, Micropoecilia, Neoheterandria, Phalloceros, Phallichthys, Priapella, Scolichthys, and other closely related genera. These are primarily freshwater fish, though some of the mollies and Limia spp. can be found in brackish or even fully marine environments. They are found from the central United States throughout Central and South America all the way to Argentina, and throughout the Islands of the Caribbean.
The next most popular family in the hobby is the small family Goodeidae. This family consists of about 39 species, plus a few more that might be separated into species as they are studied more closely. This family is exclusively found in the Mexican highlands, where many species are threatened by human activity, including introduced species, water usage for agriculture, pollution, garbage dumping, and other factors. Species that were stable just a decade ago are now fighting for their very existence in the wild. Fortunately, with just one or two exceptions, every known species is well established in the hobby, and many folks are working hard to maintain these species in their aquaria to prevent them from going extinct forever. The goodeids have become the “poster fishes” for how hobbyists can work to preserve species from extinction—without a single dollar from any government entity, hobbyists, and hobbyists alone, are preserving the entire family from extinction. Without the hobby, this entire family could disappear forever and no one would likely either know or care.
Another group that deserves mention is the Zenarchopteridae. These are the fish we hobbyists know as the halfbeaks. There are dozens of genera and species in the family, but only three genera contain livebearing species of interest to hobbyists. These are Hemirhamphodon, Nomorhamphus, and Dermogenys. All of these bizarre, surface-dwelling fish are predators that eat primarily insects in the wild. A meaty diet is required by all. Oddly, for some reason, they are often considered brackish-water fishes even though most are inland fishes found far from salty water. All nine members of the genus Hemirhamphodon are actually blackwater fish—think water similar to that of wild bettas, rasboras, and similar fish. The livebearing Zenarchopteridae are found in Southeast Asia and throughout the islands of the Philippines, Borneo, and Sulawesi.
The Anablepidae are sometimes seen in the hobby. Usually the four-eyed fish, Anableps anableps, is seen, though sometimes A. dowei is also available in the trade. They can be found as 3- to 4-inch (7.5- to 10-cm) juveniles, surprising their owners when the males grow to 8 inches (20 cm) and the females to nearly a foot (30.5 cm)! They enjoy hanging out at the surface and basking out of the water like turtles. My group loved to bask sitting on floating plants, while others have used Styrofoam or even floating turtle stands.
Their cousins the Jenynsia are sometimes available in hobbyist circles. There are a dozen or so species that have been popularized as the one-sided livebearer. Males have a gonopodium that orients either to the left or right, and females have a genital pore that opens either to the left or right. Hobby lore has it that a right-handed male can only mate with a left-handed female, or visa-versa. However, when actually keeping the fish, one can see this is a myth and will observe how resourceful and acrobatic the males can be! They can be found in southern Mexico and Central America (Anableps) and Southern Brazil, Uruguay, Paraguay, and Argentina (Jenynsia).
The final group that is regularly available is the family Syngnathidae—the seahorses and pipefish. These are primarily marine species, though several pipefish species are found in fresh water. Several seahorse species are threatened by collection for trinkets and for traditional medicines (they are believed to prevent everything from impotence to headaches). The entire genus is protected by CITES, though this is likely more of an economic benefit to the few farms allowed to produce them legally than it is a safeguard for the species, which are still collected by the ton for traditional medicines, a practice that is either exempt from or ignored by CITES.
Though the hobby gets the blame for the demise of these species, in fact all of the specimens ever taken for the hobby are likely less than what is taken in a single month for the medicinal market. The unusual reproductive strategy seahorses and pipefish use is that the female lays her eggs in the male’s pouch or on a spongy brood pad, and he fertilizes them internally and develops a placenta-like web of vascular tissue that surrounds the developing embryos and provides nourishment to them. He even goes into labor as the young are expelled!
In many species, males perform a complicated dance for the females, often including other males to show their worthiness over their rivals. Males are often brightly colored to catch the female’s attention in murky water. The intense color is usually not only appealing to the females, but also attracts predators, so it often occurs in small patches that are brought to bear only when the male is dancing to attract the female’s attention.
At other times, they hide when they can, as exemplified by Micropoecilia picta, whose colorful males can most readily be found under floating debris. In the wild, males can be seen displaying for one another out in the open while females watch the display from the safety of cover in the surrounding area. Sailfin mollies (P. latipinna) are a spectacular example of this. The males perform with their fins fully extended and their bodies at an angle to catch the sunlight.
An extreme example of females choosing their mates can be found among the halfbeaks. In captivity at least, females in the group will kill all but the most impressive male. I’ve witnessed this behavior firsthand in several Nomorhamphus species. Another extreme example is Gambusia panuco. Females of this species, at least in captivity, actually nip off the ends of most of the males’ gonopodia, allowing only a chosen few males to retain theirs.
The insemination organ is made up of several rays of the male’s anal fin and varies from species to species. In some species, such as the Jenynsia, it is little more than a tube, while in others, like some of the poeciliids, it is so distinct, with a variety of hooks and soft tissue (the palp), that it is used to differentiate the species. This organ is known as the gonopodium. It is actually inserted into the female’s genital pore, and packets called spermatophores are transferred into the female. In the poeciliids, females can retain these spermatophores for several months, so a male can father fry long after his demise.
In the families Zenarchopteridae and Goodeidae, the anal fin varies somewhat and is known as an andropodium. It is used for holding or grasping the female’s anal fin. While the two fish are held thus together, sometimes with the male wrapping his dorsal around the female too, the male fertilizes the female internally with a soft, fleshy organ called a pseudopenis. Females cannot store sperm, so each brood must be fertilized by a separate mating attempt. In some species (many Nomorhamphus species, for example), females can carry two developing broods at the same time. In the goodeids and the genera Nomorhamphus and Dermogenys, the front rays of the anal fin are modified into a clasping organ. In the Hemirhamphodon, it is the middle rays of the anal fin that are modified. In these species, the male’s anal fin can be spectacular.
In many species, the brood develops in about 28 days, while in the goodeids and some of the halfbeaks, the brood may take 50 days or longer. Some of the halfbeak females may carry two or more broods at once and may give birth to fry at unpredictable times. Generally, females “square off” a day or two before dropping their fry. This is exactly what it sounds like; they suddenly look like they’ve swallowed a block. Females should never be moved when they are close to dropping, as the stress could cause them to drop stillborn fry. In all species, once the fry are released, they are on their own. They can eat immediately, and it is a good idea to begin feeding them as soon after birth as possible. Newly hatched brine shrimp provides great nutrition and is immediately recognized as food by the newly born fry. I’ve seen guppy fry, goodeid fry, and seahorse fry begin feeding within a minute or two of birth.
Give Them a Good Home
Give them a good filter and maintain it regularly. Most livebearers like to be out in the light and need lots of open space for swimming and displaying. They like to have the bright light streaming into the water. In fact, in many species, the males look for brightly lit open areas for performing their displays. Plants around the edges and back simulate the natural areas in streams where many species make their homes. Many livebearers, especially the retail big four, make spectacular residents for community tanks. But many species do better by themselves, especially if you want to breed them—other fish species may consider newborn livebearers a delicacy.
Most livebearers can be maintained in single-species colonies with fish from newborn to mature adults all living together. Some fry will be consumed, but many will survive if the colony is well fed. An interesting thing happens in many livebearer colonies over time: Adult fish in a colony that formerly chased youngsters and considered them food will eventually come to ignore the smaller fish.