THE EFFECT OF AMBIENT pH ON ELECTROLYTE REGULATION DURING THE POSTMOULT PERIOD IN FRESHWATER CRAYFISH PROCAMBARUS CLARKII

The effects of ambient pH on postmoult net fluxes of Ca, acidic/basic equivalents (H+, NH4+/OH2, HCO3), Na and Cl2, total body Ca, haemolymph pH and electrolyte status were assessed in the freshwater crayfish Procambarus clarkii (Girard). Variables were monitored for 5 days postmoult in acidic (pH5.2; H2SO4) or alkaline (pH9.2; KOH) artificial tap water (ATW) and compared with those in control (pH7.4) tap water. In control ATW there was an initial net influx of Ca (+2700 mmolkg21 h21) and titratable basic equivalents (+5000 mmolkg21 h21) that declined with time. Calcium uptake accounted for 40% of total body Ca (0.49mmol g21); haemolymph Ca concentration remained constant. Haemolymph pH was initially relatively alkalotic (7.7) but recovered within 24h. A 20% haemolymph dilution by water uptake at ecdysis necessitated uptake of Cl2 and Na for the first 2–3 days postmoult (+1000 mmolkg21 h21). In acidic ATW, Ca and basic equivalent uptake were both 60% reduced during the first 3–4 days and total body Ca was reduced by 37%. Chloride and Na uptake and haemolymph [Cl2] were decreased. In alkaline ATW, Ca and basic equivalent uptake were elevated by 30% for the first 2 days and haemolymph alkalosis was maintained. Sodium and Cl2 balance were unaffected. Thus, ambient pH affects Ca and basic equivalent fluxes associated with postmoult calcification. Regulation of Na and Cl2 levels is also impaired in acidic ATW.