Cherax Destructor

Saturday, August 27, 2011

Cherax Destructor

Cherax Destructor

Cherax Destructor Blue

The Western Blue Yabby
The Western Yabby
Cherax Destructor
Destructor
Yabby Destructor
Cherax Davisi
Cherax Albidus
Yabby
Yabbies
Yabbie
Blue Yabby
Blue Yabbies
Cyan Yabby
Cyan Yabbies

Kingdom:     Animalia
Phylum:     Arthropoda
Subphylum:     Crustacea
Class:     Malacostraca
Order:     Decapoda
Superfamily:     Parastacoidea
Family:     Parastacidae
Genus:     Cherax
Species:     Cherax Destructor / Cherax Davisi / Cherax Albidus

Local Name : The Western Blue Yabby, Crawbob, Freshwater Crayfish, Lobby, Yabbie, , The Blue Yabby, Blue Yabby, Destractor, Destructor, Cherax Davisi, Cherax Destructor, Yabby Destructor, Yabby Destractor

Habitat : Victoria and New South Wales Australia

Water Temperature : 15 - 27 o Celcius

pH : 5 - 8

Size in Natural : Up to 10–20 cm (4–8 in) long

The common yabby, Cherax Destructor, is an Australian freshwater crustacean in the Parastacidae family. Cherax Destructor  is listed as a vulnerable species of crayfish by the World Conservation Union (IUCN), though the validity of this listing is questionable; wild Yabby / Cherax Destructor populations remain strong, and have expanded into new habitats created by reservoirs and farm dams.

Its common name of "Yabby"/ Yabbies / Yabbie is also applied to many other Australian Cherax species of crustacean (as well as to marine ghost shrimp of the infra-order Thalassinidea). Yabbies occasionally reach up to 30 cm (12 in) in length but are more commonly 10–20 cm (4–8 in) long.

Colour is highly variable and depends on water clarity and habitat; Yabby / Yabbies / Yabbie  can range from black, blue-black or dark brown in clear waters to light brown, green-brown or beige in turbid waters. Yabby / Yabbies / Yabbie  specifically bred to be a vibrant blue colour are now popular in the aquarium trade in Australia.

The everyday, or common, name Yabbie (from an aboriginal word) / Yabby / Yabbies is loosely used for several species of small freshwater crayfish in eastern Australia. The true, or scientific, name for our Yabby / Yabbies / Yabbie  in WA is Cherax Albidus. The first name is the group, or genus, of rather similar crayfish to which yabbies belong (over 30 species in Australia and PNG, including marron, koonacs and gilgies in WA). The generic name, Cherax, is thought to be a mispelling of the Greek word Charax, meaning a pointed stake - a thing that scratches. The second name (no capital letter) is the particular species, the white Yabby / Yabbies / Yabbie  which was first named as Cherax Albidus by a Victorian museum taxonomist, Dr Ellen Clark, in 1936. Our yabbies were introduced from the Wimmera farming district in western Victoria - the exact spot is known, Miram swamp near Nihil. It is an interesting coincidence that the species name for our yabbies is derived from the same Latin word ("albus" = white) which is used to describe the reflection of sunlight from our white clay dams ("albido"), where white yabbies are so successful.

Yabby / Yabbies / Yabbie are common throughout Victoria and New South Wales, although the species also occurs in southern Queensland, South Australia and 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).

Yabby / Yabbies / Yabbie are found in swamps, streams, rivers, reservoirs and farm dams at low to medium elevations. It appears Yabby / Yabbies / Yabbie  were largely restricted to lower altitude habitats in inland areas of south-eastern Australia including the Murray-Darling Basin before European settlement, with the Euastacus spiny crayfish species found in higher altitude habitats and the coastal river systems. High altitude yabby populations in Lakes Eucumbene and Jindabyne, which are on the upper reaches of the coastal Snowy River system, are unusual and may be translocated.

Yabby / Yabbies / Yabbie 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.

Yabby / Yabbies / Yabbie are primarily nocturnal detritivores, feeding primarily on algae and plant remains, at night, but also opportunistically feeding on any fish or animal remains they encounter at any time of day.

In Southern Australia it is commonly accepted that yabbies are active and thereby available to catch during the warmer months. (Colloquially any month with the letter "R" in it.) It is assumed that they hibernate during the cooler months. (citation needed)

Yabby / Yabbies / Yabbie are an important dietary item for Australian native freshwater fish like Murray cod and golden perch.

Yabby / Yabbies / Yabbie can vary considerably in overall colour and in the intensity of their shell colour patterns; some of this variation is due to age, but it is mostly camouflage to match the colour of their background. The shell and the female's deep green eggs are coloured by pigments obtained by eating plants. Juvenile Yabby / Yabbies / Yabbie  from muddy dams are normally very bland in appearance (the "white yabbie"); older yabbies are olive-greenish and more strongly marked. Darker, dirtier yabbies are ones that are not growing by making a new shell frequently; very clean, pale, often pinkish, juveniles have just cast off their old shell. Yabby / Yabbies / Yabbie  from clear, very clean waters tend to be bluish; those from green water, quite greenish; and those from tannin-coloured water, brownish.

Catching Yabby / Yabbies / Yabbie , 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 / Yabbies / Yabbie  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 / Yabbies / Yabbie  reaches the water's edge, a net is used to quickly scoop up both the meat and the grasping Yabby / Yabbies / Yabbie  in one movement.

Other methods of catching Yabby / Yabbies / Yabbie  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 as wildlife such as platypus, water rats and long-necked turtles can become trapped in them and drown.

The common Yabby / Yabbies / Yabbie  is a popular species for aquaculture, although their burrowing can destroy dams.

Yabby / Yabbies / Yabbie can also be found in private property dams where permission to fish must be obtained. Bag limits apply to yabbies in most states. For example in South Australia it is illegal to catch over 200 yabbies a day. All females carrying eggs under their tails must be returned to the water.

While less common than prawns and other crustaceans, yabbies are eaten in Australia much like crayfish in other countries. Usually yabbies are boiled, and then eaten as is or with condiments. Yabby / Yabbies / Yabbie  are also occasionally served at restaurants, where it may be prepared in salads, ravioli, pasta etc.

In New South Wales, Yabby / Yabbies / Yabbie  can be seen sold live at some fish markets such as Sydney Fish Market.

The male turns the female on her back and deposits a sperm packet (spermatophore) on her shell between the last two pairs of legs. This packet is black in rock lobsters and called a "tarspot"; we often (wrongly) call the marron and Yabby / Yabbies / Yabbie  packet a tarspot, though it's whitish in these species. The female then curls her tail under to form a chamber and picks open the male's "spermspot" to mix sperm with her eggs extruded from the openings on her middle pair of legs. She attaches the fertilized eggs onto the long fine setae on her abdominal pleopods with a glue called glar. The eggs are green at first and then black; later, the developing baby yabbie (embryo) can be seen as a yellowish spot near the egg surface. When the eggs hatch, the first stage baby Yabby / Yabbies / Yabbie  is still undeveloped, but has a large amount of yellow yolk in its oversized cephalothorax to feed on. After a moult, the next stage is more developed with less yolk left. The well developed third stage, now definitely yabbie-like in appearance, remains attached but can walk off the female to learn to feed. The attached young hang onto their mother's pleopods head down, using special snap-hooks in these stages on their back pairs of legs. After a third moult, the juveniles are truly independent of their mother, who often spawns again within a short time.

Spawning females don't feed much and, of course, they can't shed their shells to grow (i.e., ecdyse). They have been described as " shy and retiring" in nursing their eggs and, then, hatched young. The female spawners you'll actually catch in baited traps are a low proportion of what's in a dam. Fair numbers with early green eggs are caught, fewer with black eggs and very few with attached young. Some recent mothers we've recaught (last caught and marked as newly berried)after release of young, are shell-stained, indicating they've been hiding in burrows.

Yabby Spawning (Cherax Destructor) has been studied in a laboratory in South Australia where they spawned repeatedly under controlled "summer" conditions of long daylength (14 or more hours of daylength or photoperiod) and high water temperature (20oC or higher). Field observations in the east, indicate spring to autummn spawning, depending on a localitie's temperatures. Cherax Albidus spawning in our study dam at Pingelly starts in September as the temperature in shallow water rises to about 14-15oC; spawning may start earlier farther north and later in the Great Southern. Young from the spring spawning are released by December and many females then repeat spawning with a shorter incubation time, due to higher water temperatures, and release young by February. We have not seen a later, or third, wave of late summer spawning.

Size at maturity is not fixed in fish or crustacea and usually varies between individuals and under different growth conditions. Spawning females in the stunted stock we've been studying at Pingelly are predominantly in the 20-40 gram weight range, with very few (just) below 20 grams. Females just below 20 grams examined in late winter-early spring have well developed eggs in their ovaries, but can't spawn until they undergo a moult that widens their tail shell (see previous answer on external body parts). Many measurements have shown that tail broadening occurs in females in this dam at 20 grams or so; mating trials at our Waterman laboratory have confirmed that mature females can be reliably identified by this easily seen external characteristic.

Males appear to mature at a larger size than females. But which sizes of males actually mate with females may be more a question of behavioural size dominance, like bulls and rams, than potential ability. Since females spend most of the growing season spawning, and therefore not growing, males of the same age grow on to much larger sizes (50 grams and larger). Over 40 grams the claws on males start to become disproportionately larger than those of females and smaller males, and this change continues to exaggerate the claws to a massive size in males over 100 grams. As in many animals, one male crayfish can mate with many females and it is likely that the largest male Yabby / Yabbies / Yabbie  dominate smaller males and do most of the mating. Our mating trials showed that males from a dam did not mate immediately with mature females only slightly smaller than them, unlike big-clawed males. However, after some weeks these smaller-clawed males did mate.

The number of eggs increases with size of female crayfish. If the numbers of eggs in the ovaries are counted, this "potential fecundity" can be related to female size by an equation. However, the "actual fecundity" or number of eggs or hatched young on the tail of a female is always less than the potential fecundity and for yabbies the number is extremely variable for females of a given size. Some researchers have found no relationship to female size; we do have an equation with rather wide limits. Most berried females have from 200 to 400 eggs.