Observations on the Timing of Moulting Events in the Crayfish Cambarus Robustus Girard, 1852 (Decapoda, Cambaridae)

Abstract

Cambarus robustus cray sh 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 eld 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 cray sh 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 cray sh 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 cray sh species can still moult successfully. The maximum life span of C. robustus may be greater than previous estimates have indicated. RÉSUMÉ

Length-weight Relationship, Body Morphometrics, and Condition Based on Sexual Stage in the Rusty Crayfish, Orconectes rusticus Girard, 1852 (Decapoda, Cambaridae) with Emphasis on Management Implication

“…Growth of O. rusticus occurs during the spring molt. Males will molt from sexually inactive form II to sexually active form I with larger gonopods [12]. Male form I crayfish molt to form II by late summer and are sexually inactive until the following spring.…”