Ten Spotted Live-bearer

Fascinating facts about the Ten Spotted Live-bearer

• When Charles Darwin’s expedition cataloged this fish in 1843, the name ‘decemmaculatus’ was chosen for the ten-spot reference in its name, referring to the markings on its flanks.
• In the summer, the waters it calls home can warm up to 30 °C, yet the fish thrives in those shallow, vegetation-rich streams and drainage ditches across five South American countries, showing how well it tolerates heat and low-flow habitats.
• Females carry their young for exactly 24 days, then give birth to between five and ten fry that are only 2–2.5 mm long, a size so tiny they can slip through the tiniest gaps in aquarium plants.
• Because they only manage to swallow the smallest morsels, their diet in captivity must consist of live foods like Cyclops and Artemia, plus dust-like fry food, illustrating how their tiny mouths dictate a very specific feeding strategy.

At a glance

About the Ten Spotted Live-bearer

The ten-spotted live-bearer, Cnesterodon decemmaculatus, displays an elongated silhouette crowned by a small, pointed head. Its base hue ranges from olive to yellow, while a silvery belly glints beneath. Along the flanks runs a distinctive black band of seven to eleven narrow vertical stripes, the very feature that inspired its Latin name meaning “ten-spotted.” Fins are generally colorless, though the dorsal and caudal edges may darken under certain moods, hinting at a subtle emotional palette. In the shallow, vegetation-rich streams and drainage ditches of Argentina, Uruguay, Bolivia, Brazil, and Paraguay, these fish favor calm waters that can warm to 30 °C in the hottest season, a setting that supports their prolific live-bearing reproductive strategy. Males wield an angled, anterior gonopodium, while gravid females swell noticeably as gestation proceeds, culminating in a 24-day pregnancy that yields five to ten, occasionally up to fifteen, fry just 2–2.5 mm long. These juveniles quickly mature within three to four months, ready to resume the cycle in their densely planted, moderately agitated habitats, where they subsist on microscopic live foods such as Cyclops and Artemia, supplemented by fine dry fry food and even algae-laden substrates, a surprising dietary flexibility that underscores their adaptability.

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