Cherax

Cherax
Cherax destructor
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Family:	Parastacidae
Genus:	Cherax Erichson, 1846
Type species
Astacus preissii Erichson, 1846

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.

Members of the cherax genus can be found in lakes, rivers, and streams across most of Australia and New Guinea.^[1]

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.^[2] New Guinea is also home to the only known cave-living crayfish in the Southern Hemisphere, C. acherontis.^[3]

Some species are very colourful and sometimes seen in the freshwater aquarium trade.^[4]

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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.^[5]

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.^[6]

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 viable offspring.^[7] During the fight, both release urine. The female's release of urine triggers a sexual response from the male.^[7] 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.^{[citation needed]}

Once the female allows it, the male will position itself on its back, and deposit its sperm.^[8] Unlike other crayfish species, the Cherax dispar does not use its cheliped to cage females during copulation. It is mainly used during mating when the males and females fight.

In instances when displaying males have chelae of a similar size, they will engage in combat and those with the greater chelae closing force will win.^[9]

Female C. dispar uses honest signalling of strength, meaning the size of their chelae is a good indication to other C. dispar about that individual's strength.^[9] Individuals possessing larger chelae engage in more agonistic encounters and are also more likely to win.^[9] In a study of female C. dispar chelae strength, researchers found that chelae size also indirectly indicated the dominance of the female because of its honest indication of strength.^[9]

The genus contains at least 59 species:^[10][11]