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⁺/OH⁻, HCO₃⁻), Na and Cl⁻, 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 μmolkg⁻¹ h⁻¹) and titratable basic equivalents (+5000 μmolkg⁻¹ h⁻¹) that declined with time. Calcium uptake accounted for 40% of total body Ca (0.49mmol g⁻¹); 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 Cl⁻ and Na for the first 2–3 days postmoult (+1000 μmolkg−1 h⁻). 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 [Cl⁻] 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 Cl⁻balance were unaffected. Thus, ambient pH affects Ca and basic equivalent fluxes associated with postmoult calcification. Regulation of Na and Cl⁻levels is also impaired in acidic ATW.