Freshwater Crayfish Essay

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Freshwater Crayfish Introduction Over 100 species of freshwater crayfish are known from Australia. More than 20 are native to Queensland, including the worlds smallest species, the Swamp Crayfish Growth Yabbies grow only when temperatures exceed 15° C. Yabbies grow fastest at 22-28° C. Water Temperature Yabbies and redclaw both show maximum growth at about 28° C and have an upper lethal temperature (ULT) of 36° C. Redclaw start to perish at 34° C. Whereas yabbies are very tolerant of cold, redclaw juveniles repeatedly experience heavy mortality below 8° C. Water Quality Both species tolerate salinity to a level half that of seawater; however salinity levels in ponds should not regularly exceed 2ppt or growth and behaviour may be affected.Yabbies and redclaw will tolerate very low oxygen levels. Good growth rates will only be achieved if conditions are ideal (dissolved oxygen levels above 6ppm), and warm water temperatures (25°C). The critical pH range is 7-8.5. Levels much below 7 cause moulting and shell hardening problems in yabbies. Low calcium levels (hardness less than 80ppm) has the same effect. Behavior Yabbies can be aggressive and cannibalistic under certain conditions. High survival and good growth can still be achieved when some form of shelter is available. Although redclaw are less aggressive, shelter is still required to achieve uniform growth rates, as large crayfish dominate small crayfish. Unlike redclaw, yabbies are known to burrow into dam walls. Research suggests that burrowing is a survival response to a declining water level. Habitat Bottom dwelling scavengers, like to live in debris and vegetation in the water. Burrows underground during the warmer periods. Spiny Freshwater Crayfish are mainly found in eastern Australia. In Queensland they are found in the high

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