Lyretail Molly Breeding Guide

Breeding the lyretail molly, a long-finned Poecilia sphenops strain: sexing by gonopodium, hard-water conditioning, gestation and care of free-swimming live fry from birth.

Overview

The lyretail molly is a selectively bred ornamental form of the short-finned molly Poecilia sphenops, distinguished by an extended lyre-shaped caudal fin. It is a livebearing poeciliid whose wild ancestor ranges across Mexico, Guatemala and Honduras on both Atlantic and Pacific slopes, reaching about 8.4 cm standard length. Aquarium stock is farm-bred, and the fish reproduces by internal fertilization, giving birth to live, free-swimming fry.

Sexing

Males are smaller and slimmer and possess the gonopodium, a modified anal fin; in P. sphenops females grow about a centimetre larger and males cease growing once the gonopodium is fully formed. Females round out when gravid and show a darkened gravid area. The elongated fin trait appears in both sexes and is not a sex indicator.

Conditioning

Keep moderately hard or harder water with a basic pH; soft or acidic conditions weaken the fish. Seriously Fish lists 21-28 °C, pH 7.0-8.5 and 15-30 dH for P. sphenops. Feed an omnivorous diet that includes a good proportion of vegetable matter such as blanched spinach, which also supports fin development.

Mating & Gestation

Courtship is minimal; rather than displaying, males sneak up to females and attempt forced copulation. After internal fertilization the female carries the brood. Gestation in P. sphenops is roughly four to about eight weeks depending on conditions, with broods of up to about 120 fry not uncommon. Keeping several females per male reduces harassment of any one female.

Birth & Fry Care

Fry are born relatively large and accept brine shrimp nauplii or powdered flake from birth. Because adults may eat fry, use a heavily planted tank or move the gravid female to a separate tank until she gives birth. Lyretail fin development continues as fry mature.

Common Challenges

Soft or acidic water is the chief risk; the fish does better in slightly brackish water and tolerates full marine conditions. Selective lyretail lines can show weaker, more delicate fins, so feeding adequate vegetable matter and avoiding poor water quality is important. Fry predation by adults is the other recurring concern.