Cherax, commonly known as yabby/yabbies in Australia, is the most widespread genus of fully aquatic crayfish in the Southern Hemisphere. Various species of cherax may be found in both still and flowing bodies of freshwater across most of Australia and New Guinea. Together with Euastacus, it is also the largest crayfish genus in the Southern Hemisphere. Habitat Members of the cherax genus can be found in lakes, rivers, and streams across most of Australia and New Guinea. The most common and widely distributed species in Australia is the common yabby (C. destructor). It is generally found in lowland rivers and streams, lakes, swamps, and impoundments at low to medium altitude, largely within the Murray–Darling Basin. Common yabbies are found in many ephemeral waterways, and can survive dry conditions for long periods of time (at least several years) by aestivating (lying dormant) in burrows sunk deep into muddy creek and swamp beds. In New Guinea, Cherax crayfish are found widely in rivers, streams, and lakes, with a particularly high diversity in the Paniai Lakes. New Guinea is also home to the only known cave-living crayfish in the Southern Hemisphere, C. acherontis. Introduced Some species are very colourful and sometimes seen in the freshwater aquarium trade. Reproduction The mating season for Cherax is during early spring. After fertilisation, eggs develop inside the mother’s body for 4 to 6 weeks. After that period, the eggs transition to the outside of the mother's body and rest on the female’s tail. Then the eggs continue to develop and hatch in spring. Both sexes of Cherax are selective with copulation partners. Females tend to choose males with a larger central mass (abdomen and tail) and cheliped. Males tend to select copulation partners who have larger body sizes and are virgins. Opposed to females who were more dominant or had symmetrical chelipeds. As part of a mating/copulation ritual, males and females fight each other. This allows the female to test the strength of the male to determine if they will produce profitable offspring. During the fight both release urine. The female’s release of urine triggers a sexual response from the male. The male's release of urine is an aggressive response towards the fight with the female. When the male smells the female's urine it will stop releasing its own, hoping the female will allow them to copulate. Once the female has allowed the male to deposit its