Male guppies trade bright colour against predator risk
Poecilia reticulata—millionfish or rainbow fish—bears live young and thrives from northeast South America to aquaria worldwide. Flashier males win mates yet draw hunters, so high-predation streams evolve duller spots, faster maturation, and tighter schools, making guppies a living textbook of ecology and sexual selection.
Wilhelm Peters described Venezuelan fish in 1859; names bounced through Lebistes and Girardinus guppii honouring Robert John Lechmere Guppy's Trinidad specimens before Rosen and Bailey restored Poecilia reticulata in 1963. Males typically stretch 1.5 to 4 centimetres with thyroid-tuned colours; females 3 to 7 centimetres stay grey in the wild. Their wild home runs through Caribbean islands (Antigua–Barbuda, Barbados, Trinidad–Tobago), the Guianas, Brazil, and Venezuela; after mosquito-control releases they now live on every continent except Antarctica, often to the detriment of local fishes. They tolerate brackish and even full salt water.
Diets swing with habitat: upper Aripo River fish favour invertebrates; lower Tacarigua diners lean on diatoms and minerals. They show diet switching toward whichever food is commoner and forage in shoals that cut vigilance costs yet share finds—shoaling thrives under predators and fades when risk drops. Inspectors approach hunters from the side, avoiding the "attack cone," and may play tit-for-tat if partners defect. When alarmed, irises flash from silver to black, drawing strikes to the head so a matador pivot can save the body.
Two wild generations a year are typical; females first breed at 10–20 weeks and may continue to 20–34 months, while males can mature in seven weeks or less. Lifespan averages about two years. High-predation females birth more, smaller young more often. Polyandry costs females foraging time and parasite risk, yet multiply-mated mothers gestate faster and produce offspring better at schooling and escape—benefits that keep the mating scramble running.
Source: Guppy
