The molt cycle in crustaceans includes the molt itself, the development of a cuticle to harden the new exoskeleton, gonadal and so- matic growth, and the development of the next exoskeleton under the old in prepara- tion for the subsequent cycle (Passano, 1960). Four general stages or phases have been su- perimposed on this continuous process for ease of description. These are metecdysis or postmolt (stages A and B), anecdysis or in- termolt (stage C), proecdysis or premolt (stage D), and ecdysis (stage E) (Drach, 1939; Aiken, 1973). Stages A–D may be identified by reference to the state of the cephalotho- rax integument and the development of setae on the appendages using light microscopy (Aiken, 1973). Each stage, except E, is usu- ally divided into substages, the number of which vary with species. Setal development in one group of appendages is commonly used in order to standardize length and char- acter of molt stage, although the apparent molt stage will vary depending on where in the body it is measured. Molt staging tech- niques have been developed for a large num- ber of crustacean species. These include: crabs, Petrolisthes cinctipes Randall (see Ku- rup, 1964), Chionoecetes opilio Fabricius (see O’Halloran and O’Dor, 1988); fresh-water crayfishes, Cherax destructor Clark and C. al- bidus Clark (see Burton and Mitchell, 1987); stomatopods (Reaka, 1975); prawns, Litope- naeus vannamei (Boone) (see Chan et al., 1988), Litopenaeus setiferus (L.) and L. stylirostris (Stimpson) (see Robertson et al., 1987); and lobsters, Homarus americanus Milne Edwards (see Aiken, 1973), and Pan- ulirus ornatus Fabricius (see Turnbull, 1989). This paper characterizes stages within the molt cycle of the southern rock lobster Jasus edwardsii (Hutton) and discusses interspecific differences that should be noted when molt staging this species. The application of the technique to field studies is discussed. MATERIALS AND METHODS Small juvenile rock lobsters (15–17 mm carapace length (CL)) were collected from shallow water off the southeast coast of South Australia and the east coast of Tasmania during the summer of 1995. Adult lobsters (80–95 mm CL) were also collected during this period from South Australian waters using standard potting tech- niques. Molt Staging Techniques.—Forty-five juvenile lobsters were placed in individual flow-through plastic contain- ers within 500-l tanks (flow = 1,000 l/day). Each con- tainer was aerated and provided with shelters (rocks and PVC pipes) and there was no mixing of water between the individual containers or between each tank and its containers. The water temperature was maintained at 18°C and salinity at 36 g l –1 . Lobsters were fed daily on mus- sel tissue (Mytilus sp.) and pellets made from prawn heads (Fenneropenaeus merguiensis (de Man)). The adult lob- sters were placed in an aerated communal tank under the same conditions of temperature, salinity, and food. At intervals over a 5-month period, the carapace rigid- ity of juveniles and adults was noted using the method of Aiken (1973). Pleopods were removed for observa- tion under 400 and 1,000 times (oil immersion) with LEI- CA system compound and phase contrast microscopes. The degree of cuticle development and pleopod epider- mal retraction and setal formation was noted. The distal half of one pleopod was removed for each observation. Pleopod removal intervals were determined by develop- ment rate and lobster size. Intervals increased with lob- ster size (i.e., juvenile versus adult) from 1–2 days to a week during postmolt and prior to and during premolt, JOURNAL OF CRUSTACEAN BIOLOGY , 20(1): 44–53, 2000 MOLT STAGING IN THE SOUTHERN ROCK LOBSTER JASUS EDWARDSII Richard J. B. Musgrove SARDI Aquatic Sciences, P.O. Box 120, Henley Beach, South Australia, Australia 5022 (e-mail: musgrove.richard@saugov.sa.gov.au) ABSTRACT A molt staging technique is described for use in the southern rock lobster Jasus edwardsii and estimates are presented for the length of molt stage and of molt cycle in juvenile lobsters. The molt cycle can be divided into 13 stages or substages, of which 10 are relatively easy to dis- tinguish using a combination of cephalothorax rigidity, pleopod epidermis retraction, and setal for- mation. The stages are similar to those described for other lobsters and crustaceans with interspe- cific differences, including the length of D0 (apolysis) and the timing of barbule appearance. The application of this technique to field studies is discussed. 44 Downloaded from https://academic.oup.com/jcb/article-abstract/20/1/44/2419086 by guest on 19 June 2020