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

Abstract

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 Ca2- (+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.

Toxicological perspective on the osmoregulation and ionoregulation physiology of major ions by freshwater animals: Teleost fish, crustacea, aquatic insects, and Mollusca

“…Crayfish have been used frequently to study Ca 2þ ionoregulation [179][180][181][182]. Because Ca is lost with molted exoskeletons, the Ca 2þ requirement for Crustacea is substantial, and its uptake occurs mainly during postmolt following ecdysis [150,151,[183][184][185]. During intermolt, crustacean Ca 2þ requirements are met by reabsorption of up to 95% of the Ca 2þ in the primary urine [186].…”

Transepithelial Movement of Calcium in Crustaceans

“…During intermoult, there is either no net flux (Greenaway, 1976;Wheatly and Ignaszewski, 1990;Neufeld and Cameron, 1992) or only a small loss (Greenaway, 1972;Wright, 1979) of calcium, but some species lose a substantial amount of calcium immediately prior to the moult as the old cuticle is partially dissolved. Roer (1980) measured flux rates in isolated carapace tissues during the premoult period and found the flux of calcium from the cuticle to be greater than the flux in the opposite direction.…”

“…2). In still other cases, movement of calcium onto the new cuticle begins prior to the moult (Henry and Kormanik, 1985;Wheatly and Ignaszewski, 1990).…”

“…There are more reports of flux rates for the postmoult period when the net flux onto the new carapace is very high. The measurement of net fluxes across the gill is facilitated by the good correlation between apparent hydrogen excretion and net calcium uptake (Cameron, 1985;Wheatly and Ignaszewski, 1990). Calcification of the cuticle occurs by the reaction Ca 2+ + HCO3 Ϫ → CaCO3 + H + , in which bicarbonate is provided either directly from the external solution or by hydration of metabolic CO2, which results in the Greenaway, 1972Greenaway, , 1974aGreenaway, ,b, 1983Wright, 1979;Malley, 1980;Sparkes and Greenaway, 1984;Cameron and Wood, 1985;Wheatly and Ignaszewski, 1990;Neufeld and Cameron, 1992).…”

“…Filled bars represent net uptake of calcium, open bars represent unidirectional fluxes of calcium. (Data are replotted fromGreenaway, 1972Greenaway, , 1974aGreenaway, ,b, 1983Wright, 1979;Malley, 1980;Sparkes and Greenaway, 1984;Cameron and Wood, 1985;Wheatly and Ignaszewski, 1990;Neufeld and Cameron, 1992).…”