To find difference between male and female guppy fish you have to note following things. Male guppy fish are more colorful as compared to female and male have larger fins as compared to female. The most easy way to tell the difference is by looking to their anal fin. The males have more pointed and developed anal fin know as gonapodium which is used to pass sperms to females. Females have broader anal fin which look like fan. Female are larger and much rounder then males. The above one is male while below one is female. You can easily see eyes of babies inside the female's body. By the given images you can easily note the differences among guppies.
Many aquarium fishes are victims of over feeding rather then under feeding. People are not aware of the quantity which are needed by their fishes. Fishes are over dependent on their instinct. They do not realizes when to stop. Due to overfeeding they may suffer from serious problems like bloat, pot belly etc. You should feed only 2-3 minutes of food. If food is still left after 3 minutes then you are overfeeding. Also the left food is one of the main reason for polluting your fish tank.