A good way for the female to choose Mr. Right Guy is to know what sacrifices is he determined to do. This sacrifice can be something useful to her, like a good nest to live or lay eggs in. Males of the fish Gasterosteus aculeatus build nests with parts of aquatic plants and coloured debris for the female to choose. The more coloured the nest, the more females will be pleased. Another interesting behaviour is to prove the value of their genes by herculean deeds, despite of its utility to the female. Na example of it comes from another fish, Mchenga conophoros from Lake Malawi in África, in this species the male build sand-castles on the lake bed, the taller the castle the more interested females get. The curious part is that these castles are useless for females or their offspring, it only proves that a 10 cm animal can build it.