Variable Platyfish

Fascinating facts about the Variable Platyfish

• At just 7 cm (2.8 in) long, the variable platyfish packs 20–24 tiny lateral scales and 10–12 dorsal fin rays into its body.
• Unlike many of its relatives, this platyfish lacks the claw on the tip of the fifth anal fin ray, and its fourth pectoral ray is lined with well-developed serrations.
• Native to Mexico’s Atlantic slope, it has become established in canals on Tampa Bay’s eastern shore, a pond in Gainesville, and in cold springs in Montana’s Beaverhead, Granite, and Madison counties.
• In Hong Kong the species’ “prodigious breeding” has been blamed for harming native fish, illustrating how an aquarium favorite can become an ecological disruptor when it escapes into the wild.
• Aquarists keep it in water as cool as 16 °C (61 °F) up to 24 °C (75 °F), and scientists have used it for genetic studies.

At a glance

About the Variable Platyfish

The variable platyfish (Xiphophorus variatus) is a modest-sized livebearer, reaching up to 7.0 cm (2.8 in) in length. In its native streams of southern Tamaulipas and northern Veracruz, the fish displays an olive base colour flecked with black marbling or spots along the caudal peduncle, while large males carry striking blackish blotches on the dorsal fin. Unlike many of its congeners, X. variatus lacks the claw at the tip of the fifth anal fin ray, and its fourth pectoral ray bears pronounced serrae, tiny saw-like notches. The male’s gonopodium is needle-like, contrasting with the female’s broader, triangular anal fin, a sexual dimorphism that hints at the species’ prolific breeding capacity. In the wild, this platy inhabits slow-moving, vegetated canals, ditches, and warm springs, thriving on an omnivorous menu of algae, plant fragments, small crustaceans, insects, and annelid worms. Its tolerance for cooler water, comfortably between 16 °C and 24 °C (61 °F and 75 °F), has made it a staple of the aquarium trade, where its ever-changing colour patterns and hardy nature attract hobbyists worldwide. A surprising trait is its ability to establish self-sustaining populations far beyond its native range, having colonised canals on the eastern shore of Tampa Bay, Florida, springs in Montana’s Beaverhead, Granite and Madison counties, and even distant locales such as Colombia, Singapore, and Hong Kong, where its prodigious breeding has begun to pressure native fish communities.

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