EFFECTS OF EXTREME PH ON THE PHYSIOLOGY OF THE AUSTRALIAN YABBY CHERAX DESTRUCTOR - ACUTE AND CHRONIC CHANGES IN HEMOLYMPH OXYGEN LEVELS, OXYGEN-CONSUMPTION AND METABOLITE LEVELS

Respiration and metabolism of the freshwater crayfish Cherax destructo r were investigated with respect to the acidification and alkalization of its environment. Crayfish were exposed for up to 504 h (21 days) t o pH 4.5, pH 7.1 (control) or pH 8.0 water and oxygen consumption rate , haemolymph oxygen transport and haemolymph glucose and lactate conce ntrations were determined, The effect of reducing environmental [Ca2+] in acid water from 500 to 50 mu mol l(-1) was also examined. In acid water (500 mu mol l(-1) Ca2+), oxygen uptake by Cherax was reduced by 79% after 504 h (21 days) compared with 'control' animals (pH 7.1, 500 mu mol l(-1) Ca2+), Haemolymph lactate concentration (mean remained t hat was not glucose concentrations were regulated within the range of control values (0.32+/-0.01 mmol l(-1)). The arterial-venous Co-2 diff erence of Cherax haemolymph decreased after 288 h and Pa-O2 increased from 11.1+/-0.5 mmHg to 42.4+/-1.0 mmHg between 96 h and 288 h, Decrea sed oxygen uptake and delivery without compensatory increases in anaer obiosis or glucose levels describe a hypometabolic response to low pH. The hypometabolic response of Cherax was greater in alkaline water as shown by a 53% reduction in O-2 uptake rate compared with a 44% reduc tion in acid-exposed (500 mu mol l(-1) Ca2+) animals after 96 h, This decrease in M(O2) Of alkaline-exposed animals was correlated with decr eased haemolymph glucose levels (from 0.32+/-0.01 at 0 h to 0.06+/-0.0 1 mmol l(-1) at 96 h). Lowering the [Ca2+] of the water both increased the magnitude of the effects of acid exposure and elicited further ch anges in haemolymph oxygen transport, The maintenance of high haemolym ph P-O2 during pH stress appears to reduce the involvement of haemocya nin, since this promotes decreased a-v C-O2. Hypometabolism probably p ermits Cherax to conserve resources that might otherwise be used, howe ver, for growth and reproduction, The implications for the fitness of the animal are discussed,