How soon can a pair of guppy start spawning?
Some male guppies will start developing sexual characteristics as early as three weeks, while on the average about 4 to 6 weeks.
Females at this time is best to be separated from the male (sexing them) before they start spawning. Young male guppies with strong sex drives can relentlessly chase females, often to exhaustion. If you are not sexing them, it’s best to maintain a 2:1 ratio (females to males).