Molly / Platy / Swordtail (Livebearers)

Overview

Molly, Platy, and Swordtail are three closely related livebearing fish from Central America - hardy, colourful, peaceful, and prolific. With Guppies, they form the four most common livebearers in the hobby. Excellent for community aquariums.

Natural History

Molly (Poecilia sphenops, P. velifera, others)

Native to Central America and Mexico. Larger than other livebearers, often kept in slightly brackish water.

Platy (Xiphophorus maculatus, X. variatus)

Native to Mexico and Central America. Smallest of the three.

Swordtail (Xiphophorus hellerii)

Native to Central America. Named for the long sword-like tail extension on males.

Appearance

• Molly: 7-13 cm (sailfin molly females reach 13 cm).
• Platy: 4-6 cm.
• Swordtail: 10-13 cm including male's sword.

All come in many colours - black, red, blue, orange, gold, calico, and many tail and fin variations.

Temperament & Tankmates

Peaceful. Excellent community fish with other peaceful species. Males can chase females persistently - keep ratio of 1 male to 2-3 females, or all-male groups (with adequate space to prevent aggression).

Tank Size & Setup

• Platy: minimum 75 L (20 gallon) for group of 5.
• Swordtail: minimum 110 L (30 gallon).
• Molly: minimum 110 L (30 gallon).

Water Parameters

• Temperature: 22-28°C.
• pH: 7.0-8.5 (alkaline preferred).
• Moderate to hard water.

Mollies appreciate slight salt (1 tsp/10 L) - but check tankmate tolerance.

Diet

Omnivore with high vegetable preference. Quality flake or pellet food, blanched vegetables (spinach, peas, zucchini), occasional protein. Mollies especially need algae and plant matter.

Health & Lifespan

3-5 years (Platy 3-4, Swordtail and Molly 4-5).

Common concerns:

• Ich.
• Shimmies (Molly disease) - neurological symptoms from water quality, temperature, or salt issues.
• Fin rot.
• Inbreeding decline - modern strains often weak; choose from reputable breeders.

Pros & Cons

Pros: colourful, peaceful, easy, breed reliably, beginner-friendly. Cons: breed prolifically (mixed-sex tanks fill rapidly), modern strains often inbred, Mollies prefer slightly brackish water.