OBSERVATIONS ON THE TIMING OF MOULTING EVENTS IN THE CRAYFISH CAMBARUS ROBUSTUS GIRARD, 1852 (DECAPODA, CAMBARIDAE)

Abstract

Cambarus robustus crayfish kept and monitored under constant summer-like photoperiod and temperature conditions in the laboratory did not moult during the winter months. The timing of the moulting events in the laboratory closely matched the timing of the corresponding types of moults in the field for adult Form I and Form II males, adult females, and juveniles of both sexes. The juveniles moulted during a less restricted period of time than the adults. The Form I to II adult male moults occurred only in the late fall, during a very narrow period. There is preliminary evidence that the timing of moulting in this northern, surface water crayfish species is governed by an endogenous circannual rhythm. This endogenous mechanism is capable of regulating the moulting cycle in C. robustus for long periods of time, even in the absence of any changes in external factors such as water temperature and photoperiod. Such a circannual endogenous rhythm would allow the crayfish to anticipate and prepare, both physiologically and behaviourally, for certain upcoming, predictable seasonal changes in the environment, such as the arrival of winter. Very large, and, presumably, very old individuals of this crayfish species can still moult successfully. The maximum life span of C. robustus may be greater than previous estimates have indicated.