Cherax tenuimanus, known as the hairy marron or Margaret River marron, is one of two species of crayfish in Southwestern Australia known as marron. It occupies a narrow range within the southwestern biogeographical region of Margaret River. It is currently listed as critically endangered on the IUCN Red List, because of the threat from the wider ranged smooth marron, Cherax cainii, which was introduced to its habitat. Recent studies have shown that adding mannanoligosaccharide (Bio-Mos) to the diet of Cherax tenuimanus can increase their immunity and rate of survival. Description The hairy marron ranges in color from olive green to brown to black, with females sometimes having red or purple patches on their undersides. Adult hairy marrons grow to between 300 and 400 mm with a body consisting of a head and thorax that are protected by a carapace. The body eventually extends into an abdomen that ends in a muscular tail, and the body is bracketed by 5 pairs of legs including two pairs of pinchers; a larger pair for capturing prey and defense and a second, smaller pair for fine manipulation of food. The hairy marron can be differentiated from the smooth marron by the hairy bristles that are known to sometimes cover its carapace and other body parts, although these bristles can be difficult to observe in juveniles. Diet The hairy marron is an omnivore whose diet mainly consists of small invertebrates, fish eggs and larvae, and algae. It is also a cannibal that will potentially eat its own young. Habitat The hairy marron lives in exclusively freshwater habitats, specifically in clear, oxygen-rich water in the Margaret River in Southwestern Australia. Its range has become limited to 3 major pools in the upper portion of the river due to competition with the smooth marron. Exact environmental parameters needed for the survival of the hairy marron are unknown due to the low number of individuals in natural settings. However, studies performed in aquaculture settings have shown that hairy marron survive best in water that is about 25 degrees Celsius and that with a salinity of at least 100 mg/L. They also prefer habitats with debris or other structures they can use as shelter or as food sources if the material is organic. Reproduction Hairy marrons begin to mate when they reach sexual maturity during the second and third years of their lives, with their mating season occurring between