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Journal of Experimental Biology 151,469-483 (1990)
Published by Company of Biologists 1990

Electrolyte and Gas Exchange during the Moulting Cycle of a Freshwater Crayfish

MICHELE G. WHEATLY ¹ and LORI A. IGNASZEWSKI ²

¹ Department of Zoology, University of Florida Gainesville, FL 32611, USA
² Department of Medical Sciences, College of Veterinary Medicine, University of Florida Gainesville, FL 32611, USA

Whole-animal net electrolyte fluxes (Ca²⁺, apparent H⁺ , titratable acidic equivalents, ammonia, Na⁺, Cl^-, K⁺, Mg²⁺, phosphate and sulphate) and respiratory gas exchange were monitored throughout the moulting cycle in juvenile freshwater crayfish Procambarus clarkii (Girard) at 21 °C. Intermoult crayfish were essentially in ion balance. As crayfish approached ecdysis (-3 days, where t=0 is the day when the cuticle is shed), there was a net efflux of Ca²⁺ (-1000µmolkg^-1 h^-1) correlated with a corresponding uptake of acidic equivalents (or base output) of +2000µmolkg^-1 h^-1. Following ecdysis, both fluxes switched vector; uptake of Ca^2- (+2000µmolkg^- h^-) and basic equivalents (+4000µmolkg^-1h^-1) were completed within 6 days. The moulting cycle also affected fluxes of electrolytes other than those involved in CaCO₃ resorption and deposition. Crayfish remained in Na⁺; and C^-; balance from intermoult up to ecdysis. Following ecdysis, both were taken up actively at rates of around plus;500µanolkg^-1h^-1 for 3 days, presumably restoring the haemodilution that would have resulted from water loading. A premoult efflux of K⁺ was partially offset by postmoult uptake. Meanwhile, crayfish experienced increased efflux of phosphate following ecdysis, probably because of increased integumentary permeability. Rates of O₂ uptake (MO₂) and CO₂ excretion (Mco₂) increased to peak values (double intermoult rates) immediately prior to ecdysis. While MO₂ recovered during postmoult, Mco₂ dropped precipitously, significantly reducing the gas exchange ratio. Since the Mco₂ deficit agreed well with the postmoult basic equivalent uptake, the latter is probably attributable to HCO₃^- uptake for calcification.

Key words: crayfish, moulting, calcium, acid-base balance

Accepted on March 29, 1990

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