Atlantic Molly Care Guide
The Atlantic molly (Poecilia mexicana) is a hardy Central American livebearer tolerant of fresh, brackish and even hypersaline water.
Compiled by Aquairi from published sources · Published · Updated
Overview
Poecilia mexicana, the Atlantic molly, is a livebearing fish described by Steindachner in 1863. FishBase lists a maximum standard length of about 11 cm, with females larger and deeper-bodied than the more slender males. The body is brown above and grades to golden-yellow below.
Taxonomy
- Family: Poeciliidae
- Genus: Poecilia
- Scientific name: Poecilia mexicana
- Described by: Steindachner, 1863
Habitat
The species occurs on the Atlantic slope of Middle America, from the Rio San Juan and the Rio Bravo basin in Mexico south through Central America. According to FishBase it inhabits warm springs and their effluents, canals, weedy ditches and stream pools. It tolerates fresh, brackish and salt water, with reported salinities up to about 32 ppt, and two notable cave populations live in sulphidic, oxygen-poor water containing hydrogen sulfide.
Tank requirements
- Minimum tank volume: 100 L
- Temperature: 22-30 °C (72-86 °F)
- pH: 7.5-8.5
- GH: 12-30 °dGH
- Lifespan: 3-5 years
- Water: hard, alkaline; tolerates brackish conditions
Diet
The Atlantic molly is an omnivore. FishBase notes that its food is mainly detritus, and Wikipedia describes it feeding chiefly on algae and detritus, including filamentous algae and diatoms scraped from surfaces. In aquaria it accepts vegetable-based flakes and benefits from algae grazing.
Compatibility
This is a peaceful, mid-water fish suited to hard-water community tanks. It does best with other hard-water species and other mollies, and should not be combined with soft-water fish whose requirements conflict with its preference for alkaline, mineral-rich water.
Breeding
Poecilia mexicana is a livebearer. FishBase reports that females give birth to roughly 30-80 young about 28 days after fertilisation and reach sexual maturity at 7-12 months. Breeding occurs year-round, and males use forced mating rather than elaborate courtship.
Conservation status
IUCN Red List: Least Concern (assessed 22 March 2018).
Atlantic Molly Breeding Guide
Overview
Poecilia mexicana, the Atlantic or shortfin molly, is a hardy livebearing poeciliid native to the Atlantic slope of Middle America, from the Rio Bravo in Mexico south through Central America to Costa Rica. It tolerates fresh, brackish and saltwater, recorded at salinities up to 32.4 ppt, and inhabits shallow coastal lagoons, estuaries, ponds and rivers, usually in water less than 1 m deep.
Sexing
The maximum standard length is about 95 mm, and males occur in multiple size classes from 18 mm to over 70 mm. Females are larger and curvier, while males are more slender and carry a gonopodium. As in related mollies, males do not perform courtship displays and instead attempt forced copulation.
Conditioning
The species is primarily a benthic algae grazer; stomach contents are largely filamentous algae, diatoms, fragments of vascular plants, detritus and other decaying organic matter. A vegetable-rich diet therefore conditions adults well. Its tolerance of brackish and even high salinity means it thrives in hard, alkaline water.
Mating & Gestation
Fertilization is internal via the gonopodium, and the species shows near-continuous breeding, likely producing young monthly. Brood sizes range from 13 to 35 embryos, rising to 100 or more in large females. Females store sperm, allowing repeated broods after a single mating.
Birth & Fry Care
Fry are born free-swimming and take small live and prepared foods from birth, including fine vegetable matter reflecting the algae-grazing adult diet. Dense planting or moving the gravid female to a separate tank protects fry, as adult mollies will eat young. Because the species occupies shallow coastal lagoons, estuaries and ponds usually less than 1 m deep, a broad, well-planted setup with surface cover suits both adults and fry.
Common Challenges
Frequent, near-monthly broods can quickly overpopulate a tank, so managing numbers is important. Soft or acidic water is unsuitable; the fish prefers hard alkaline conditions and is remarkably salt-tolerant, recorded at salinities up to 32.4 ppt, so brackish maintenance is an option that can also help suppress disease. Its broad tolerance makes it one of the more forgiving mollies to keep and breed.