All freshwater crayfish belong to one of three taxonomic families. Two of these, Astacidae and Cambaridae, occur only in the northern hemisphere of Australia. The remaining family, Parastacidae, is restricted to the southern hemisphere and contains 13 different genera (or groups) including Cherax. There are 30 species of Cherax throughout Australia, of which marron (Cherax tenuimanus), redclaw (Cherax quadricarinatus) and yabbies (Cherax destructor) are the most well known and the most popular aquaculture species’.
As for all crustaceans, yabbies do not have a skeleton (internal bone structure), but have an exterior hard shell, known as an exoskeleton. Easily distinguished from the true spiny freshwater crayfish which is characterised by the presence of spines on the exoskeleton, the yabby has a smooth shell. The colour of the shell varies greatly depending on the location, season and water conditions in which the yabby is found. Colour will also vary from individual to individual in one location. They are usually a drab olive, dun or light brown colour, but have also been found to range from black, ochre-yellow and brown to red and blue.
The basic anatomical characteristics of the yabby are illustrated. The body of the yabby may be broadly divided into two sections; the abdomen (tail) and the cephalothorax (head). In yabbies, the tail meat, which is important to the farmer, makes up 15-20% of the total body weight when they have been headed and shelled. The head, and other internal organs, is protected by the carapace and armoured at the front with a strong, pointed rostrum. The major sensory organs for crayfish are the large feelers or antennae and the finer, more central feele known as antennules. The eyes, although quite prominent in the head, are of little use in the murky environment in which the yabby lives. Thus, the antennae and antennules act in place of the poor eyesight as touch and taste sensor locating potential food as well as sensing changes in wate quality parameters such as temperature and salinity.
The abdomen is divided up into six segments that are individually encased in hard shell. A flexible membrane joining each segment allows the yabby to move relatively unhindered. Appendages located on the underside of abdominal segments two to five are known as pleopods (or swimmerets). These are very important for female crayfish as the edge of each pleopod is lined with fine hairs, or setae, to which they attach their eggs.
|Common Name: Yabby|
Scientific Name: Cherax destructor (Illustrated)
Status: Native, Freshwater
Exoskeleton: Hard supporting external structure of arthropods and some sponges. The exoskeleton is formed from calcium.
Gastrolith: Calcareous deposit located within the stomach of crustaceans. Calcium is stored in this way just prior to a moult in order to conserve calcium reserves.
Gonopore: Reproductive, or genital, opening.
Omnivore: Animal that eats both plants and animals.
Pereiopod: Walking limb of crustaceans. There are five pairs of walking limbs found on the cephalothorax.
Pleopods: Swimmerets found on the underside of each abdominal segment of crustaceans.
Setae: chitinous hair, or bristle, found along the edge of the pleopods of crustaceans.
Spermatophore: a number of sperms enclosed in a sheath of gelatinous material.
Swimmeret: Small paired appendage present on the first five abdominal segments of crustaceans. Swimmerets are possibly used by females to attach fertilised eggs during incubation.
Telson: The unpaired terminal abdominal segment of crustaceans.
Uropod: Fan-shaped paired appendage found on the final abdominal segment of crustaceans. The uropod is used in swimming.