The common yabby (Cherax destructor) is an Australian freshwater crustacean in the Parastacidae family. It is listed as a vulnerable species of crayfish by the International Union for Conservation of Nature (IUCN), though the wild yabby populations remain strong, and have expanded into new habitats created by reservoirs and farm dams.
Other names frequently used for Cherax destructor include the blue yabby or cyan yabby. Its common name of "yabby" is also applied to many other Australian Cherax species of crustacean (as well as to marine ghost shrimp of the infraorder Thalassinidea).
Taxonomy
During a wet season, an Australian yabby can travel kilometers across land in search of new water in which to make its home.
The word "yabby" comes from yabidj which was the term for freshwater crayfish in several Aboriginal Australian languages that were spoken in what is now known as Victoria, including the Wemba Wemba language and the Woiwurrung–Taungurung language.
Physical description
Yabbies are on average 10–20 cm (4–8 in) in length, but have been shown to grow to lengths of up to 30 cm (12 in).
The common yabby has a smooth shell with one pair of post-orbital ridges. It does not have a spine on the shoulders behind the cervical groove (region that separates head from thorax). Females have a reduced growth rate after maturity which usually means that they are smaller in size compared to their male counterparts
Colour is highly variable and depends on water clarity and habitat; yabbies can range from black, blue-black, or dark brown in clear waters to light brown, green-brown, or beige in turbid waters. Yabbies specifically bred to be a vibrant blue colour are now popular in the aquarium trade in Australia.
Dissemination
Yabbies are common in Victoria and New South Wales, although the species also occurs in southern Queensland, South Australia, and throughout parts of the Northern Territory, making it the most widespread Australian crayfish. It has been introduced to Western Australia, where it is an invasive species and poses a threat to other Cherax crayfish species native to the region, such as gilgies (Cherax quinquecarinatus). It is also occasionally introduced to Tasmania, where due to the island state's fragile ecosystem it's also considered an invasive species.
The common yabby has the largest distribution of any freshwater species currently in Australia as it lives within the inland river systems of both central and eastern Australia, which extends over nearly the entire continent.
Due to its widespread abundance and ability to become an invasive species, yabbies can survive in a large range of climates from warm tropics to the cool and temperate plains and highlands. They also are found in a variety of freshwater environments, including both turbid water holes and clear permanent flowing streams and lakes. With its varied dissemination and limited movement, there are also often morphological changes between different populations of common yabbies as well.
Yabbies have 2 pairs of antennas which they use to sense their environment through tactile and chemical methods. The first pair of antennas are smaller and are located near the top of the head, inside the larger secondary antenna pair. This first pair plays a larger role in the detection and interpretation of chemical stimuli within the environment, allowing yabbies to detect and respond to chemical signals dissolved in the water. These signals can correspond with food sources, predators, or conspecifics and can be detected over short distances. The second, larger pair of antennas are long and flexible and contain mechanoreceptors that use physical touch to allow the yabby to receive information about the distance to, size, and shape of nearby objects. By constantly exploring their environment, yabbies use these mechanoreceptors to gradually map out their surroundings in combination with their chemoreceptors used to detect food, predators, or mates. Similar sensory systems that utilize both mechanoreception and chemical sensing have also been observed in other freshwater crayfish species including the Australian freshwater crayfish Euastacus Spinifer.
These auditory signals are often used to communicate with conspecifics about mating, grouping, and other communication. According to studies, yabbies have also been known to emit these sonic signals in response to receiving another chemical or acoustic signal. In the dark and turbid waters which these animals live in, the usage of these acoustic signals is extremely vital for effective communication that circumvents the limited light that penetrates past the surface of the water. It is still currently being studied what each signal communicates but it has been shown that these sounds are not consistently tied to specific behaviours.
Due to an ability to extract organic nutrients efficiently from many different food sources, yabbies often use a non-selective approach to obtaining prey as juveniles, being carnivores, herbivores, and detritivores.
Some examples of natural food in which yabbies can extract nutrients from include detrital forage, soil benthos, soil substrate, and peron. Like some other freshwater crayfish, yabbies can ingest in bulk and selectively process organic nutrients to feed themselves.
However, further studies have shown a mechanism of response in Cherax Destructor that allows them to be more tolerant to low-temperature environments and contribute to their strong adaptability to survive in various climates through Australia. Although weight gain, length gain, and molting rates all decreased when temperature was lowered, research shows activity of antioxidant enzymes, pathways against endocrine disorders, glucose metabolism, antioxidant defense, and immune responses were upregulated to compensate for and protect against diminished environmental temperatures. As a result, the ability of yabbies to adapt to even low-temperature environments is increased through these mechanisms to further their ability to act as an invasive species in a variety of different locations.
Environmental stressors
Environmental stressors affecting the common yabby include chemical pollutants such as neonicotinoids, a type of pesticide, which significantly impact physiological and behavioral functions. Even acute exposure can impair neurological function and behaviours due to changes made to the nervous system. Some disruptions include lowered feeding efficacy, worse avoidance of predators, reduced overall fitness, and other narcotic-like effects which can lead to worsening fitness. In-depth studies have also shown that accumulation of neonicotinoids can lead to a build-up of reactive oxygen species (ROS) and reduced activity of antioxidants, leading to significant cell damage over time.
Life and reproduction
Clutch size, brood size, development rate, and other reproductive factors of yabbies vary significantly depending on both genetic and non-genetic factors. Studies have shown that some phenotypic factors, such as female body weight, were positively correlated with clutch and brood size although brood sizes were often lower than clutch sizes. In addition, environmental factors like temperature were negatively correlated with developmental time which ranged from 33.4 to 42.2 days, indicating a faster rate of development at higher temperatures within a certain range. However, these results also showed large variability even within the same species Cherax Destructor.
In the European Union, it is included in the list of invasive alien species of Union concern and hence cannot be imported, bred, transported, commercialized, or intentionally released into the environment in any of its member states.
Catching
Catching yabbies, or "yabbying", in rivers and farm dams is a popular summertime activity in Australia, particularly with children. The most popular method involves tying a piece of meat to a few metres of string or fishing line, which in turn is fastened to a stick in the bank, and throwing the meat into the water. The string is pulled tight when a determined yabby grasps the meat in its claws and tries to make off with it. The line is then slowly pulled back to the bank, with the grasping yabby usually maintaining its hold on the meat. When the meat and the grasping yabby reaches the water's edge, a net is used to quickly scoop up both the meat and the grasping yabby in one movement.
Other methods of catching yabbies involve various types of nets and traps. Local fishing regulations must be checked before using any nets and traps for yabbies; many types of nets and traps are banned or restricted, as wildlife such as platypus, water rats, and long-necked turtles can become trapped in them and drown. Yabbying is also a term used in southern New Zealand for catching Paranephrops zealandicus.
Aquaculture
thumb|Week-old yabby eggs, 2–3 mm, attached by minute hairs to underside of female abdomen, [[CSIRO]]
The common yabby is a popular species for aquaculture, it is illegal to catch over 200 yabbies
Yabbies as food
While less common than prawns and other crustaceans, yabbies are eaten in Australia much like crayfish in other countries. Usually, yabbies are boiled and eaten plain, or with condiments. They are also occasionally served at restaurants, where they may be prepared in salads, ravioli, pasta, etc. Prior to cooking, it is advisable to 'purge' the yabby in clean water, this helps to clear the gut of any muddy flavour, resulting in sweeter tasting meat.
In New South Wales, yabbies can be sold live at some fish markets such as Sydney Fish Market. In Victoria, whole yabbies can be purchased cooked and ready to eat at Queen Victoria Market.
Conservation status
Although they are not considered an endangered species, they are considered to be vulnerable by the IUCN. Here, vulnerable refers to how this species may face a high rate of extinction in the wild. This is because their habitat is under constant threat from agricultural chemicals like fertilizers and pesticides. Also, degradation of native vegetation also makes their habitat more vulnerable.
Although this organisms habitat is under threat they are still considered a very adaptive species and are involved in very rapid breeding