Saturday, December 10, 2011

Yabby, Yabbies (Cherax destructor) Habiat In Aquatic

The freshwater crayfish commonly termed the yabby, Cherax destructor, is often referred to as an ideal species for aquaculture in Victoria. While production estimates arevaried, the 120 licensed farmers in Victoria produced 10 and 25 tonne of yabbies during 1995-1996. Prices for yabbies are influenced by demand, quality and size of product, with live yabbies falling into the mid to upper price range for shellfish.

Yabby farming is often carried out at the lowest and easiest level, known as “extensive” aquaculture. The production system is simple and initial cost of farming is low as most farmers utilise existing dams that have been built for the watering of agricultural livestock. Once established in dams, yabby populations often become self-sustaining and very little needs to be done by the farmer to enhance production. Although the initial cost of farming is low and establishment of yabbies in dams is relatively simple, issues such as uncontrolled breeding, post harvest handling and maintainence of a high quality product for market, need to be considered. Live yabbies that are quality assured attract the highest prices on the domestic and international markets.

Attempts to improve the farming of yabbies using purpose built ponds will increase productivity however, a cost benefit analysis is necessary and shall be based on realistic production return estimates. A basic but sound understanding of the animal’s anatomy, physiology and behaviour is an essential pre-requisite to successful yabby farming. Information presented in this Aquaculture Note represents only the most basic aspects of biology specific to Cerax destructor and it is recommended that further literature, including the references listed at the end of this Series Note be read to obtain a more complete understanding of the subject if you are contemplating a successful aquaculture venture.

Yabby Habitat

The yabby, Cherax destructor, is a semi-aquatic freshwater crayfish commonly found in a wide range of habitats throughout most of Victoria and New South Wales, including low-lying swamp ground, streams, rivers and dams. The most wide spread species of freshwater crayfish, the yabby may also be found in southern Queensland, South Australia, and parts of the Northern Territory. Yabbies are generally found in areas where oxygen levels are high and where there is plenty of vegetation.

Adapted to a wide range of temperatures, the yabby is able to survive in water temperatures between 1°C and 35°C however, when water temperatures drop below 16°C the yabby falls into a state of partial hybernation where metabolism,  feeding and growth virtually cease. Temperatures higher than 35°C will result in cessation of growth and eventually mortality. The ideal temperature range for optimum growth is between 20°C and 25°C.

Yabbies are able to tolerate a wide range of dissolved oxygen levels and elevated salinities. Research has shown that they are capable of surviving in sea water for approximately 48 hours however, high salinity levels will result in increased stress on the individual. Growth will often cease in salinities over 8 parts per thousand (ppt), which is equal to approximately one quarter that of seawater, and mortalities will occur as salinity levels increase. Dissolved oxygen levels are also important. As dissolved oxygen decreases, feeding and therefore growth, also decreases.

Hence, good feeding activity and optimal growth are achieved when salinity levels are lower than 8 ppt and are dependent on healthy, well oxygenated waters. Yabbies are commonly found on muddy or silted bottoms and are rarely found in clear water habitats, preferring water with moderate levels of turbidity. Muddy waters afford some protection from predators such as fish and birds giving the yabby a better chance at survival.


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