Aquatics Unlimited: Articles: Livebearing Fishes
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Livebearing Fishes

for the week of 9/29/99

Some of the most popular freshwater aquarium fish, including guppies, mollies, swordtails and platies, deliver fully formed young, as opposed to the vast majority of fishes, which lay eggs. Scientifically, these fish are said to be viviparous, or even more technically, ovoviviparous (meaning the pre-born fry feed off egg yolk rather than directly from the mother).

Keeping livebearers - is not difficult. Most are fairly hardy if kept in well-filtered, heated aquariums. Most seem to benefit from a tablespoon of aquarium salt per 5 gallons of water (for mollies, this is nearly a requirement), which seems to eliminate the white slimy patches that many would otherwise get. Frequent small feedings are preferred to occasional, larger ones. A minimum of two females per male should be purchased to reduce competitive aggression and over-ambitious courtship.

Breeding livebearers - requires almost no effort by the aquarist, other than to make sure both males and females are present in the same tank. Sex can easily be determined by looking at the anal fin (the unpaired fin under the fishes belly). Females have a normal fan-shaped fin (similar to the two ventral fins nearby), while males have a rod-shaped organ that points straight back.

Birthing livebearers - as the due date approaches, pregnant females exhibit pronounced abdominal swelling, and the eyes of the babies can often be seen through their sides. The expectant mother should ideally be moved to a separate tank of 5 gallons or larger, properly set up, and with plenty of hiding places for the babies. Some mothers will not eat their own young, but all other fish would be happy to. Commercial "breeding traps" are too small for most adult females, and should only be employed as a last resort.

Rearing baby livebearers - most baby livebearers are able to eat powdered dry foods and baby brine shrimp within a few hours of birth. Babies should be treated to the same clean, healthy, warm, salted conditions as adults.


"Tip of the week" appeared regularly in 1999 and 2000.

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