#2 The females gonopodium is typically fully expanded outward, and the males is usually tucked up toward his body and really only comes down during brief moments before mating with another guppy. The gonopodium is an anal fin used to impregnate. However, both sexes are capable of expanding and contracting their gonopodium.#3 At the end of the abdomen you may notice an often dark almost circular area which is called the gravid spot, if your fish has one then its a female. The gravid spot tends to change colors from pink to almost black(sometimes a combination of both), the color differs depending if the guppy has eggs inside of her or not. When the female has eggs/fry inside her the under belly will appear fuller and her body more rounded in shape(as seen above) and she may even start to develop a hunched/slumped spinal appearance.
#4 Males and females tend to act differently, the females being more submissive and independent and the males are more often found schooling together, perhaps acting a bit more aggressive and generally sexually mature males chase after the females.
#5 Adult females are generally larger then adult males, it also seems as most females continue to give birth their bodies seem to continue to get larger, where as the males seem to stop growing.