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Livebearer Fish Deserve Respect

Mollies, guppies, platies and swordtails are all livebearer fish.

By Philip A. Purser |

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Platies and Swordtails
Of all the livebearing fish in pet shops today, none holds such a special place in my heart as the platies. Among all the danios, mollies, hatchets and neon tetras I had over the years, one red platy survived to see them all come and go. He lived for more than seven years and died at a whopping 2 inches long, the average being less than 1½ inches. Belonging to the genus Xiphophorus, the platies and swordtails hail from Mexico, Belize, Guatemala and Honduras. They are robust fish that are hardy and tolerant of a wide range of harsh conditions.

Their toughness makes them a fine choice for the beginning hobbyist, while their vibrant coloration can add a touch of beauty to any aquarium. Like guppies and mollies, platies and swordtails are subject to color variation within different populations of the same species, and are selectively bred for these traits. The cultivated forms - and there are a lot of them - tend to grow larger and live longer in the aquarium than wild species.

When purchasing platies or swordtails, look for smaller, less developed individuals with shorter swords and smaller stature. These will be the youngest of the bunch and should provide you with a more rewarding experience. The older, larger fish that are still in shipment may be more aggressive or stressful toward tankmates once you get them home. Large adults can also be violently territorial, often nipping or harassing other fish. It is best to select smaller individuals, so they can "grow up" in your aquarium.

Both platies and swordtails are suited for life in the community aquarium. The fancy varieties (such as the lyretail swordtail, hi-fin swordtail and swordtailed platy) may prove somewhat problematic in an aquarium of fin-nippers, such as tiger barbs. These flamboyant fish may be targeted and harassed by their tankmates, and might do better in a species aquarium or one that is large enough to grant each fish its own territory.

Swordtails, as noted, may demonstrate a degree of aggressiveness toward others of their own species, as well as other tankmates. This is especially true of males. One male, therefore, should be housed with a number of female swordtails or alone. Providing one male with a harem of females will go a long way in curbing his aggressive tendencies. Most platies, on the other hand, are tolerant, mild-mannered fish that can easily coexist with a wide range of other tropicals.

Platies and swordtails thrive in a neutral to slightly basic pH (7.0 to 7.5), and benefit greatly from a planted aquarium. As is true with guppies, platies and swordtails will nip and pick at these plants to augment their diet, but will also accept flake foods, tablets, lettuce, peas, bloodworms, mysis shrimp and other tiny crustaceans/aquatic larvae. Although most do not have the tiny frame and weak fins of fancy guppies, these fish do not do well in aquariums with a lot of current. Less powerful filtration, such as bio-wheels or trickle systems, is best, as these fish thrive in calm, peaceful waters.

Although platies and swordtails will breed in captivity, their propagation tends to be a bit trickier than most livebearers. Male swordtails are distinguishable from females by both their gonopodium and sword projection on the tail fin. Do not be fooled, however - some males may go their entire lives without ever growing a pronounced sword. Reliable sexing is attained only through the absence or presence of the gonopodium. The females of both platies and swordtails also exhibit a darkened patch toward their vent, which expands or contracts based on her degree of pregnancy; very pregnant fish will exhibit a very large dark patch.

These fish tend to mate with just about anything they can get a hold on and can easily hybridize, thereby rendering the offspring infertile. This occurs when too many generations of the same bloodline continue breeding. When successful broods are produced, the fry are quite fragile and may be physically stunted if not given a sufficient amount of a proper diet.

If you wish to breed either platies or swordtails, set up species aquariums designed for breeding. These aquariums should be large (20 to 55 gallons) because the developing fry need a great deal of space if they are to mature without physical deformities. Fry may be reared on the same foods as adults (ground-up flakes, shrimp nauplii, brine, and other minute foods are appropriate).

When the fry of these or any other species of poecilid emerge, they will need hiding places to feed and grow. If left in open water, these minuscule fish will almost certainly be eaten. Mature clumps of Java moss will work just fine. The moss provides cover for the fry, while at the same time affording them plenty of vegetative food. The only major drawback with all poeciliids is that if housed in poor water conditions, these fish are prone to contract whitespot disease (ich) and other bacterial infections. If caught soon enough, these problems are easily treatable, but are even more easily preventable through regular water changes and responsible husbandry practices.

Other Poeciliids
The world of livebearing fish does not end with mollies, guppies, platies and swordtails. Despite the wide variety of these fish, there are more poeciliids that might have a place in the aquarium. Inhabitants of the southern United States, Central and South America, and the Caribbean Islands, they come from a range of habitats. The spotted tail or true mosquitofish may live in mountain streams at elevations of more than 8,200 feet, yet it fares equally well in brackish coastal waters at zero elevation.

The remaining poeciliids also represent a broad spectrum of sizes and lifestyles, ranging from the diminutive and docile merry widow (Phallichthys amates), which grows to no more than 1 inch long, to the highly predatory pike livebearer, which reaches nearly 8 inches in length and sports an imposing mouthful of needlelike teeth. In common with the rest of the Poeciliidae family, these remaining members are an excellent choice for the young or beginning hobbyist. They are hardy, beautiful fish (even the pike livebearer, despite its propensity for carnage, is a blue-green gem to behold) that can add color and variety to any aquarium.

If you do decide upon one of the lesser known poeciliids, it is worth your while to research your choice before bringing it home. Make sure it will coexist with your aquarium's current inhabitants and that you can fulfill its captive requirements. Some species of poeciliids are prone to jumping at night or when they get nervous, so it is best to keep the aquarium covered at all times.

Some of the best suited of these fish to the community aquarium are true mosquitofish (Heterandria bimaculata) and the slap-sided blue-eye (Priapella compressa), while the bishop fish (Brachyrhaphis episcopi) and the knife livebearer (Alfaro cultratus) are nervous, edgy fish that are more difficult to keep in captivity. With the exception of the pike livebearer, all species of Poeciliidae are omnivores, and all can benefit from the diet described for the guppies or platies.

The poeciliids are a wonderful family of fish with a great deal to offer to the hobby. Many are colorful, elegant creatures that add a bit of spice to the average aquarium in their natural or cultivated forms. Given a little know-how on the part of the hobbyist, almost any species or combination of livebearers can thrive for years in the home aquarium.

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Reader Comments

Nora    Wichita, KS

7/5/2012 4:33:57 PM

Fantastic & well written article! I especially loved the part referring to guppies: "Introduced to some new areas when they survived being flushed down the toilet."

All I can say about that is-WOW!!

Julie    Gilbert, AZ

8/24/2009 6:09:44 PM

What a great article. I didn't know that mollies could survive in a saltwater aquarium. Thanks for all your informative articles, I enjoy reading them.

kt    Nashville, TN

2/1/2009 9:26:15 PM

having just recently gotten back in to aquariums after about a 20 year absence and having been given incorrect info from the salesperson at the lfs this was indeed helpful

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