The lethal and sublethal effects of increased salinity on adult and juvenile crayfish, and the effects of increased salinity on osmotic behaviour of adult crayfish were investigated. Lethal experiments, using a wide salinity range, indicated little difference in the salinity tolerance of adults and juveniles, but when 96-h median tolerance limits were estimated using a narrow salinity range: the juvenile value was 25. Sow while that for adults was 29.90‰. Sublethal effects, as determined by 'threat' and 'escape' behavioural responses with increased salinity, indicated that normal behaviour in adults and juveniles is maintained up to c. 12‰, lost between c. 12 and 25‰,. and death results above c. 25‰,. It is suggested that the field salinity tolerance range of C. destructor is restricted to salinities where behavioural patterns are unaffected. C. destructor is a hyperosmotic regulator, maintaining its blood concentration at approximately 410 mOsm up to 14‰, above which the blood concentration follows the isosmotic line. The possible evolution of this species is briefly discussed in terms of osmotic behaviour.
Small (0.08 to 6.1 g) crayfish were grown at 26�C under three treatments: held individually and fed 3% or 10% of body weight per day, or held communally and fed the higher ration. Moult increments, expressed as length or weight increment (%), were smaller and intermoult periods were longer in the crayfish held communally or, particularly, in crayfish fed low rations; this resulted in lower growth in these treatments. Crayfish from three geographically discrete populations held individually and fed the higher ration showed relationships between log moult increment in weight and log premoult weight; further, the length of the intermoult period increased with size for these populations. Models for average growth showed that C. destructor may grow from 0.1 g to 40 g in approximately 230 days. Growth may have been suppressed in the culture system because of the size of containers, the entirely artificial diet and the variable water quality.
Setal development through the moult cycle has been observed in the uropods and telson of the freshwater crayfish Parastacoides tasmanicus. The changes in the morphology of the setae through the moult cycle can be used as a moult stage index for this decapod. The initial formation of the setae (stage D1) for this crayfish differs from that hitherto described for other macrurans.
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