In a study about Trinidadian guppies published in October 2011, researchers found that when an aggressive male was chasing a group of females, the females are more likely to fight each other. Males chase and nip the females, stressing them out so much that they are distracted from protecting themselves from predators and even searching for food. Reacting to stress by getting irritable sounds familiar, doesn't it?
Females emit pheromone three days a month, but males will still pursue unreceptive females because they can still store sperm for later. They prefer fertile females if one is available but will take whatever is available.. Researchers found that females who aren't interested in sex will pair off with prettier females to take the attention of the males. It works, too.
Guppies flit from one social group to another, but have favorite partners for hunting for food and protection from predators. Researchers think that leaving the social group to form the pair with the prettier female is detrimental to the uninterested females.