HEMOLYMPH ECDYSONE AND ELECTROLYTES DURING THE MOLTING CYCLE OF CRAYFISH - A COMPARISON OF NATURAL MOLTS WITH THOSE INDUCED BY EYESTALK REMOVAL OR MULTIPLE LIMB AUTOTOMY

In studies of crustacean molting eyestalk removal (ER) or multiple lim b autotomy (MLA) has traditionally been used to precipitate ecdysis. T his study was undertaken to determine whether the general physiologica l condition of the crayfish Procambarus clarkii, at 23 degrees C, indu ced to molt. either by ER or MLA, is comparable to that of animals mol ting naturally. Hemolymph was sampled every 2 d up to and for 3 wk fol lowing ecdysis. Samples were assayed for ecdysone (as an endocrine mea sure) and inorganic electrolytes (Ca, Na, CI, K, Mg), which were selec ted for study since regulatory hormones originate in the eyestalk. Fol lowing surgery, ER crayfish underwent lethal ecdysis within 13 d, soon er than MLA crayfish (36 d). In the control group ecdysone peaked appr oximately 5 d before ecdysis. For induced molts, the ecdysone peak was two times larger and was more protracted. Calcium was elevated 15 d b efore natural molts as a result of cuticular reabsorption, then return ed to baseline level and exhibited a transitory decrease at ecdysis as a result of water loading. The MLA crayfish had a similar Ca profile, except that the peak occurred earlier and in advance of the ecdysone peak. A premolt Ca peak was not observed in ER crayfish; levels of all ions were greatly reduced at ecdysis because of excessive water uptak e. The ecdysone and Ca profiles did not appear to be linked in any tre atment. Sodium and Cl profiles were very similar in all treatments, es sentially decreasing as a result of water uptake around the time of ec dysis. Potassium remained constant in control crayfish, In MLA crayfis h it decreased around the time of ecdysis, and in ER crayfish it exhib ited both a postsurgical decrease and a more pronounced decrease at ec dysis. Magnesium in control and MLA crayfish decreased in premolt and remained low, Possibly contributing to exoskeletal mineralization; how ever, levels were elevated in ER crayfish. Collectively, the data demo nstrate that ER crayfish experience severe hemolymph dilution at ecdys is as a result of increased water influx which may contribute to death . The eyestalks appear to contain factors that regulate water and elec trolyte balance. Although MLA crayfish molted successfully, the profil es for ecdysone and electrolytes, while superficially similar to those of control crayfish, were sufficiently different that the two groups cannot be considered physiologically or metabolically equivalent.