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A Marine Option Program Ski11 Report

AN ASSESSMENT OF MOLTINB METHODS FOR CULTURINGSOFT-SHELL CRABS IN HAWAII

Richard H. HorivchiSteven S. Ogata

Clayward K.M. Tam

WORKING PAPER NO. 47

NATIONAI SEA GRANT DEPOSITORYPELL LIBRARY BUILDING

URI. I'IARRAGANSITI BAY CAI.",":USN,lBRAG~'i,".',"".EI|, R I 028�2

November 1981

University of HawaiiSea Grant Co'liege Program

Honolulu, Hawaii

The finding and views expressed in this working paper do not reflectthose of the University of Hawaii or the University of Hawaii Sea GrantCollege program. Any commercial product or tradename mentioned herein isnot to be construed as an endorsement.

AHSTRACY

In the sof' t-shell state arhieh occurs immediately after a molt, theblue crab Callinectes sapidus! is considered by many people to be adelicacy. To pz'ovide information for prospective businesses consideringculturing this crab for' sale as a gourmet item, a study a>as conducted byMarine Option Program students on the Likelihood of' increasing crab moltfrequency. Among the criteria studied, temperature regulation, inducedZimb autotomy a ref'Zez to drop an injured appendage from t' he body!, anda selection process foz premoLt stage crabs ver~e given major emphasis.

Temperature regulation ms found to be ineffective in determiningthe likeHhood of increasing molt frequency of Late intezmolt the peziodof metabolic reserve accumulation! aM premoLt the peziod of molt prepz-r'ation! stage crabs. Molt f'requency of crabs ms unaffected in optimumtemperature mter �9' to 80'C'! when compared mth molt frequency in roomtemperatuz'e mter �l' to 2b'C!. It. appears that the influence of tem-peratuz'e is greatest during the early intermolt stage vhen tissue growthis at' a rnazunum.

Induced Hmb autotomy vas also found to be ineffective. Accordingto the literature, it is necessary to remove sm to eight Hmbs of earlyintermolt stage crabs to elicit ecdysis the act. of shedding the oLdendoskeleton!. In this study all animals subjected t'o Limb autot'omy diedprior to ecdysis.

The selection process was founa to be the best method for determiningthe HkeHhood of increasing molt frequency and increment in crabs. Cri-teria for selection vere based on age, condition including the effecfsof handling and cz'ab stage!, sex and separation of the developing ezo-skeleton in the swimming Legs, food intake, and non-induced limb autotorny.Males and juvenile femaZes vere chosen foz specimens; adult females verefound to be undesirable because they are in terminaZ anecdysis final,non-molting stage!, This study also found that crabs which are not readyto shed, and those vith five missing limbs but with adequate Limb budgrowth, generally completed the molting process. In addition, a highpercentage of successfu'L molts vas obtained vhen the separation of thedeveloping ezoskeZeton in the ~rimming Legs ~ere 0.2 mm foz females and0.8 mm foz maZes. As for food intake, crabs that did not consume foodwithin Mo days after being p'Laced in the tank weakened and died ratherthan resumed eating. Finally, survival of crabs exhibiting non-inducedLimb autotomy vas severely limited.

TABLE OF CONTENTS

INTRODUCTION ~ 1

MATERIALS AND METHODS.

~ ~

~ ~ ~ ~~ ~

RESULTS. 5

ACKNOWLEDGMENTS. 12

REFERENCES CITED 13

APPENDIX 17

LIST OF FIGURES

Figure

~ I i 2

Areas of measurement to determine the separationwidth in blue crab swimming legs . . . . . . . . . , . , ~ . 8

10

10

Temperature Regulation.Induced Limb Autotomy .Selection Process .Molt Frequency and Increment.

Temperature Regulation.Induced Limb Autotomy ~Selection Process .Molt Frequency and Increment.

DISCUSSION AND CONCLUSIONS .

Temperature Regul ation.Induced Limb Autotomy .Selection Process .

Structures of some ecdysones .

A selection process of premolt stage crabs .

Average separation width of the developing exo-skeleton in blue crab swimming legs against daysto molting .

Average separation width of 0 mm in swimmingleg of Callinectee sapidu8

Average separation width of 0.4 mm in swimmingleg of Callineatea Bapidus

Average separation width of 0.6 mm in swimmingleg of Callinectea sapidus with "pink sign"� to 10 days to ecdysis!.

3

4

4 4

5

55

11

11

111.2

TABLE OF CONTENTS continued!

Figure

LIST OF TABLES

Table

Effect of Temperature on Molt Frequency in LateIntermolt and Premolt Stage Blue Crabs ofDifferent Sizes.

Effect of Temperature on Holt Increment in LateIntermolt and Premolt Stage Blue Crabs . 6

Holt Increment and Frequency of Size Classes .

Average separation width of 0.6 mm in swimmingleg of Callinectea sap~du8 with "red sign"� to 3 days to ecdysis! . . . . . . . , . . . . . . . . . . 10

INTRODUCTION

Information about efficient rearing techniques is essential for themass cultivation of aquatic species. One species being considered forintensive culture in Hawaii is the blue crab, Callinect'e8 aapidue. Inthe soft-shell state--after it has just undergone a molt--almost theentire crab is edible since the exoskeleton has not had time to calcify.In this state, the crab is considered a gourmet item.

Blue crabs, not indigenous to Hawaii, are abundant along the easternand southern shores of the United States. In such places as Maryland,Virginia, Delaware, North Carolina, Florida, and Louisiana, most of thecrabs are caught as "peelers" and retained until they molt. Peelers arecrabs with pink to red signs in the swimming legs Haefner and Garten,1974!, indicating that they are close to molting. The pinkish color inthe last two sections of the swimming legs of the developing new shellindicates that ecdysis will take place in 3 to 10 days. The pinkishcolor takes on a reddish color when ecdysis is 0 to 3 days away. Themolting process takes place during the "buster" stage when the epimeralline a ventrally located predetermined splitting region! is brokenthrough resorption. The buster crab will molt within 15 minutes' to 38hours.

In temperate regions, molting is seasonal. Crabs migrate to deeperwaters and bury themselves for the winter--usually from November untilthe first two weeks of April Hall, 1970!. But, depending on food avail-ability and favorable water temperature, molting can occur at other times.The climate in Hawaii is suitable for producing soft-shell crabs year-round.

A study was conducted to determine which method or methods would bepractical for use in increasing the likelihood that molt frequency andincrement will occur at shorter intervals in order to produce soft-shellblue crabs intensively in Hawaii. Both a literature search and laboratoryexperiments were conducted. Among the methods considered were: �! eye-stalk ablation; �! tying off the eyestalk with filament; �! X-organ andsinus gland removal; �! ecdysone injection or ingestion; �! temperatureregulation; �! induced limb autotomy; and �! a selection process.

The literature abounds in information on the effect of eyestalk abla-tion on precocious molting of crustaceans Abramowitz and Abramowitz, 1940;Fingerman and Fingerman, 1976; Passano, 1960; Skinner, 1968!. Accordingto Skinner and Graham �972!, eyestalk ablation is accompanied by a mor-tality rate of 100 percent during ecdysis, With eyestalk ablation, onlypartial emergence from the former exoskeleton takes place. Manual peelingaway to the carapace at this time is not possible because the limbs stillremain attached ta the former exoskeleton.

Other methods such as tying off the eyestalk with filament, X-organand sinus gland complex removal, and ecdysone injection or ingestion leadto the same result. Produced within the eyestalk X-organ is the molt-inhibiting hormone which prevents the onset of a molt by repressing the

production of ecdysone by the Y-organ. The latter organ is situated oneither side near the anterior end of the branchial chamber Passano,1960!. Ecdysone stimulates the synthesis of RNA and protein in the hepa-topancreas Gorell et al., 1972! and is common to all organisms belongingto the phylum Arthropoda, although their chemical structure may vary,The relative abundance of ecdysone in crustaceans and other arthropods islow. About 2 mg of crustecdysone were isolated from 1,000 kg of the mar:i,neshrimp, Jaeue laKandei Goad, 1978!. Three ecdysones--crustecdysone andCallinecdysones A and 8 Figure 1!--were isolated from the blue crab Goad,1978!.

OH

HO

0- hydroxyecdysone!

HO OHCH~ OH

HO

HO 0OH CH

HO

HO

Figure 1. Structures of some ecdysones Goad, 1978!

Because the literature search on the abave-mentioned methods revealedthat their use resulted in high mortality rates, they were ruled out forfurther consideration. The remaining three methods--temperature regulation,induced limb autotomy, and a selection process--were studied in greaterdetail through a literature search as well as laboratory experiments.These are discussed below.

MATERIALS AND METHODS

Specimens obtained from Henry Oates, a seafood dealer who has live.blue crabs flown in to Hawaii from Louisiana, were selected from shipmentsfor the seafood market. For the three methods, juvenile females and thosethat appeared in good condition active, and non-lacerated carapace! werechosen. The experimental animals were juvenile females mean carapacelength of 52.9 mm + range of 7.1 mm, N = 118! and males mean carapacelength of 54.3 mm + range of 3.7 mm, N = 48!. Carapace length, defined asthe distance between the groove adjacent to the rostrum and the midpointof the carapace-abdomen overlap, was measured with a vernier caliper,Adult females, identified by the broad triangular gray abdomen, wereundesirable due to their state of terminal anecdysis see item Cr,T in theappendix!.

The animals were held in a. recirculating seawater system in EdmondsonHall on the University of Hawaii Manoa campus. Although a higher incidenceof incomplete ecdysis occurs with recirculated water �5 percent! than withnew water �8 percent! Haefner, 1971!, recirculated water was used becauseof its convenience. The 2 ft x 8 ft x 1 ft holding tank, made of 3/4-inplywood and fiberglass, was divided by plexiglass into 24 compartments, A2 ft x 3 ft x 1 ft biological filter system containing dolomite �-mmmesh! was used, A water pump and PVC pipes provided aeration and watercirculation. Readings taken using a dissolved oxygen meter ranged fram5.2 to 5.7 ppm, In the study done by Lewis and Haefner �976!, oxygenconsumption was related to animal size and was highest during the premoltstage of the life cycle as compared with the molt and postmolt stages; amaximum total oxygen consumption of about 4.5 mg/1 per/hr was recorded forblue cxabs with carapace widths ranging from 93 to 125 mm. Crabs used inthis study were comparable in size. Waste and food material were swept byan undercurrent to the outflow ax ea. New water from the seawater system,at a rate of two to five gallons per minute, was provided. Salinity fluc-tuated during the course of this study, ranging from 15 to 30'/� . Theoptimum salinity for overall growth is 15'/« Hall, 1970!.

The animals were fed fish fillets twice daily and supplemented withcod liver oil. Pieces of U2ua and other types of seaweed were occasion-ally placed in the compartments, A blue crab's diet in nature consists ofa number of animal and vegetable materials {Hall, 1970!.

Temperature Regulation

The optimum temperature for the shortest malt frequency is 29' to30'C Holland et al., 1971!. Beyond this level, as temperature increases,malt increment decreases Leffler, 1972!. A comparison was made between

room temperature water �1' to 26'C! and water heated to the optimum tem-perature using thermostatically controlled aquarium heaters to determineif the latter had a favorable effect on molt frequency and to determinethe effect on molt increment for crabs relatively near molting. Lateintermolt and premolt stage crabs see appendix! were used. Both moltperiod and the final carapace length were recorded.

Induced Limb Autotomy

According to Skinner and Graham �972!, limb autotomy speeds up themolting process but only for crabs in the intermolt stage and it. is neces-sary to remove six to eight limbs to elicit ecdysis. Also, it is the num-ber of limbs removed and not the total weight or volume that is the primedeterminant of precocious molting Fingerman and Fingerman, 1976!. Lateintermolt stage crabs delay their molt for limb regeneration and premoltstage crabs proceed to molt, resulting in the loss of the autotomizedlimbs Skinner and Graham, 1972!.

Crabs in the early intermolt stage, which were distinguished by theabsence of separation of the developing exoskeleton in the swimming legs,were randomly selected and six of their limbs subjected to autotomy.This was accomplished by cutting to cause damage to the merus first majorsection of a limb, adjacent to the carapace!.

Sex, size, and molt frequency data were recorded where possible.

Selection Process

Since there is a limited supply of blue crabs in Hawaii as comparedwith on the mainland, study specimens included more than from the pink tored sign crabs. Selection was based on a number of criteria: age, condi-tion including the effects of handling and crab stage!, sex and separationof the developing exoskeleton in the swimming legs, food intake, and non-induced limb autotomy. In general, males and juvenile females with thepotential for survival were chosen.

Holt Frequency and Increment

As the size of the crab increases, usually the average intermoltperiod and increment also increases Leffler, 1972!. To predict pxoduc--tion output per unit of time, information on molt frequency and incrementis necessary.

Carapace length, molt frequency, and increment for each size classwere estimated. Molt fxequency is the number of molts per period of time.Carapace length was measured to the nearest whole number befoxe and aftex'molting to determine size incxement.

RESULTS

Temperature Regulation

The effect of temperature on molt frequency in both late intermoltand premolt stage blue crabs is shown in Table 1. Due to limited samples,the data cannot be considered completely representative but there isenough information for a tentative conclusion: the average molt frequencyat optimum temperature is comparable with that at room temperature.

TABLE 1, EFFECT OF TEMPERATURE ON MOLT FREQUENCY IN LATE INTERMOLT ANDPREMOLT STAGE BLUE CRABS OF DIFFERENT SIZES

Class Molt

Frequency days!

TemperatureMolt Frequency

days!

Water

Temperature 'c!

Size Class in mm

number of crabs!

21 to 26 10. 8

10.429 to 30

As shown in Table 2, there is no significant difference betweenoptimum and room temperature water on molt increment in late intermoltand premolt stage blue crabs,

Induced Limb Autotomy

Crabs subjected to limb autotomy died either before or during molting.The average survival period was about 30 days. Hence, no molt frequencyand increment data were obtained.

Selection Process

Figure 2 shows the process of crab selection for molting.

48 to 49 �!50 to 51 �.!51 to 52 �!52 to 53 �!53 to 54 �!54 to 55 �!58 to 59 �!

48 to 49 �!50 to 51 �!51 to 52 �!52 to 53 �!53 to 54 �!54 to 55 �!58 to 59 �!

4 to 88 to ll9 to 20

10 to 12

4 to 78 to 256 to 7

54 to 11

41

599

26

TABLE 2. EFFECT OF TEMPERATURE ON MOLT INCREMENT IN I ATE INTERMOLT

AND PREMOLT STAGE BLUE CRABS ZERO TO ONE LIMB MISSING!

F i na I Ca rapace Leng th mm!Initial

Carapace Length ! 21 to 26'C 29' to 30'C

52 to 53

53 to 54

MARKET CRABS IMMEDIATEI YAGE

'Aduit femalesCON

Weak crabs Includinp bustersLacerated ar seriously infected exoskeleton, limb s!,

or limb bud s!Greater than five limbs missing unless regeneration index

is greater than 9, or separation width in the swim-ming legs is greater than 0.3 mrn

Loss of limb s! durIng shipmentSEX AND SEPARATIO

IN SWIMMING LEGSJuvenile females: width of at least O,I mmMales: width of at least 0.3mm

FOODThose not consumlnp foad within two days except pink

sign and red sign crabsNON-I

AU TOTOIItI YLass of limb s! without inducement

SOFT- SMCA NDIDATES

Figure 2. A selection process of premol t stage crabs

Only adult females are undesirable due to their state of terminalanecdysis.

48 to 49

50 to 51

51 to 52

58 to 59

59 to 60

59 to 62

57 to 58

63 to 64

59 to 60

56 to 57

59 to 60

62 to 63

62 to 63

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Condition

Weak crabs including buster stage crabs are not likely to survivethrough ecdysis. Also, animals which have their exoskeleton, limb, orlimb bud lacerated or seriously infected are not likely to survive. Infec-tion is caused by chitinoclastic bacteria Cook and Lofton, 1973!. Thenumber of limbs lost affects survival, too. Generally, as more limbs arelost, the chance for survival decreases. However, if a crab has sufficientlimb development, with regeneration indexes Bliss, 1959, 1960; Bliss andBoyer, 1964! greater than 9, it will likely survive through ecdysis

th of limb bud

carapace length regeneration index�

Those crabs that lose their limbs during shipment are less likely to sur-vive.

Sex and se aration of the develo in exoskeleton in the swimmin le s

The mortality rate is lower if the average width of separation in thelast two segments of the swimming legs is at least 0.1 mm for females and0.3 mm for males. The separation width is measured in the modified pro-podus and paddle of the swimming legs adjacent to the joint Figure 3!.The greater the separation, the closer the crab is to ecdysis.

Modified propodueFigure 3. Areas of measuremeto determine the s

ration width in bl

crab swimming legs

Overall, the percentage of female crabs surviving through ecdysis ishigher 84 percent! than for male crabs SO percent!. However, if theregeneration index is greater than 9, or if the separation width of thedeveloping exoskeleton in the swimming legs is at least 0.3 mm, the sur-vival rate of male crabs 83 percent! approaches that of female crabs.

The separation width is dependent on the size of the animal, crabshaving carapace lengths ranging from 45,8 to 59.0 mrrr have an averageseparation width of from 0 to 0.8 mm. The average separation width canbe correlated with days to molting Figure 4!. Figures 5 through 8 showexamples of increasing separation widths, indicating that the crabs areclose to molting.

50

40

Vo

O O20

C! lO 0 0 O.I 0.2 0,3 0.4 0.5 0.6 0.7 0.8AVERAGE SEPARATlON WIDTH me!

Figure 4. Average. separation width of the developing exoskeletonin blue crab swimming legs against days to molting

10

Figure 5. Average separation widthof 0 mm in swimming legof Ca22inectes sapidus

Figure 7. Average separation widthof 0.6 mm in swimming lego f Ca LLinectea, apiau,".wi th "pink sign'' � to 10days to ecdysis!

Figure 6. Average separation widthof 0.4 mm in swimming legof Ca22inectes sapidu8

Figure 8. Average separation widthof 0.6 mm in swimming legof Ca22inectr, aapiauawith "red sign" � to 3days to ecdysis!

Food intake

Crabs which do not consume food for a period of two days will notremain alive for long. The mortality rate for these crabs is close toIOO percent. However, crabs with pink or red signs in their swimminglegs that do not take in food are very likely to survive through ecdysissince their glycogen requirement has been stored,

Non-induced limb autotom

Except for pink to red sign crabs, those crabs which exhibit. non-induced limb autotomy are likely to die before molting. The mortalityrate for these crabs was found to be 93 percent N = 15!.

Nowt Frequency and Increment

Factors which determine carapace size increase are the number ofmissing and regenerating limbs and days spent in the tank Table 3!. Thefewer the number of missing and regenerating limbs and days spent in thetank, the better the chances of increasing molt frequency, and vice versa,Generally, as lost limbs increase in number, molt increment decreases.Also, as time in the tank increases, molt increment decreases. The combi-nation of lost, regenerating limbs and extended period in the tank resultsin even greater molt increment decreases.

DISCUSSION AND CONCLUSIONS

Temperature Regulation

Temperature plays a major role in the metabolism rate of poikilothermic cold-blooded! organisms. For the juvenile blue crab, growth increaseswith increasing temperature until an optimum temperature �9' to 30'C! isreached, Growth and survival then decrease at temperatures above 30'C Holland et al., 1971!.

It appears that temperature regulation is most effective for specificstages of the molt cycle--stages at which there is metabolic activitycritical for molting. It was hoped that the optimum temperature wouldhave a significant effect. on increasing molt frequency. Results showthat this is not the case for late intermolt and premolt stage crabs sincemetabolic processes in these stages were generally past the criticalperiod. The early intermolt stage seems to be the period of criticalmetabolic activity for precocious molting since it is the main period oftissue growth.

Induced Limb Autotomy

Even though the outcome of molting of a crab with autotomized limbsis a smaller product when compared with an intact crab Skinner andGraham, 1972!, it was hoped that the supply of soft-shell crabs would beconsistent. This was not the case.

Reports by Skinner and Graham �972!, Fingerman and Fingerman �976!,and Weis �976! state that limb autotomy is an effective method for induc-ing precocious molts. Carapace widths in those studies ra~ged from 15 to53 mm. The average carapace width in this study was about 80 mm. Mortali-ties may have been due to poor nutrition since the survival period of crabswith six autotomized limbs was about 30 days. The loss of limbs stimulatesprecocious molting, but may decrease the crab size increment becauseresources are used instead to regenerate limbs as observed in this study.,This supports the poor nutrition theory for mortalities. Also, quantita--tive nutrient requirement levels are greater for a larger juvenile animalthan for a small one.

Sel ecti on P voce s 5

Many crabs appeared to be stress victims due to shipping conditions,.Weak crabs, the mortality of buster stage crabs, limb autotomy during ship-ment, food refusal, and non-induced limb autotomy while in the water wereprobably stress-induced when considering crabs which have not been sub-jected to shipping conditions. The mortality of other crabs appeared tobe nutrition related. However, stress victims can be reduced to a minimumwith proper handling. The problems of overpacking and lack of moistureare severe when crabs are shipped to Hawaii. The crabs are packed in abox about five deep without, provision for moisture. With improvedhandling procedures, the process of selection could be minimized.

Selection of crabs is thus extremely important for increasing thelikelihood that molt frequency will occur at shorter intervals. Malesand juvenile females, with all limbs intact and no infections and withseparation widths of at least 0.3 mm and 0.1 mm respectively, are goodmolting candidates. Those that molt successfully are ideal for sale asa gourmet item.

AC KNQWLE DGMENTS

We acknowledge all the people and organizations who advised andencouraged us in carrying out our Soft Shell Crab Project, especiallyDr. S.R. Haley, associate professor of zoology, University of Hawaii,whose knowledge and expertise were invaluable.

Special thanks go to Randy Nishimura who initiated this project, andJohn McMahon, Sue Hampson, and Al Kam of the Marine Option Program fortheir advice and guidance. Also thanks to Henry Oates, whose proposalsparked our interest in this project, for the initial capital outlay andsupply of crabs.

Thanks also to Dave Onizuka of the Anuenue Fisheries Research Center

for the donation of the dolomite, Dr. S.A. Reed for the use of lab equip-ment, and Karen Tanoue for her patience and thoughtful editing of thismanuscript.

12

REFERENCES CITED

Abramowitz, R.K., and A,A. Abramowitz. 1940. Molting, growth, and sur-vival after eyestalk removal in Vca pugilatox'. Biol,. Bull. 78:179-188.

Bliss, D.E. 1959. Factors controlling regeneration of legs and moltingin land crabs. In Physiology of Insect Development, ed. F.I. Camp-bell, pp. 131-144. Chicago, Illinois: University of Chicago Press.

Bliss, D.E. 1960. Autotomy and regeneration. In The Physiology ofC~stacea, ed. T. Waterman, Vol. I, pp. 561-589. New York: AcademicPress.

Bliss, D.E., and J.R. Boyer. 1964. Environmental regulation of growthin the decapod crustacean Gecaxcinus latex'alis. Gen. Comp. Zndocr'in.4:15-41.

Cook, D.W., and S,R. Lofton. 1973. Chitinoclastic bacteria associatedwith shell. disease in Penaeus shrimp and the blue crab Callinectessapidus!. J. Vildl. Dis. 9:154-159.

Fingerman, S.W., and M. Fingerman. 1976. Effects of time of year andlimb removal on rates of ecdysis of eyed and eyestalkless fiddlercrabs, Vca pugilatox'. Max. Biol. 37:357-362.

Goad, L.J. 1978. The sterols of marine invertebrates: composition,biosynthesis, and metabolites. In Maxine Natural Px'oducts, ed. P.J.Scheuer, Vol. II, pp. 75-172. New York, San Francisco, London.Academic Press.

Gorell, T.A., L.I. Gilbert, and J.B. Siddall. 1972. Studies on hormonerecognition by arthropod target tissues, Amex'. Zool.. 12:347-356.

Haefner, P.A., Jr. 1971. An approach to shedding blue crabs Callinectessapiaus in a recirculated seawater system, Amex. Zoot. 11:211.

Haefner, P.A., Jr,, and D. Garten. 1974, Methods of handling and shed-ding blue cx'abs, Callinectes sapidus. Mar. Resources Advis. Ser. 8.Virginia Inst. Mar. Sci. 14 pp ~

Hall, W.R., Jr. 1970. Dekmaxe 's blue crab. University of Delaware'sSea Grant Marine Advisory Service Program. Nll. 6 pp.

Holland, J.S., D.V. Aldrich, and K. Strawn. 1971. Ef'fects of tempera-tu2"e and salinity on groa!th, food convexsion, survival and tempera-tux'e xesistance of juvenile blue cxabs, Callinectes sapidus Rathbun�TAMU-SG-71-222. Texas ASM University Sea Grant Publ. 166 pp.

Leffler, C.W. 1972. Some effects of temperature on the growth andmetabolic rate of juvenile blue crabs, Collinectes sapidus, in thelaboratory. Mar. Biol. 14.104-110.

13

Lewis, E.G., and P.A. Haefner, Jr. 1976, Oxygen consumption of the bluecrab, Callineotes sapidus Rathbun, from proecdysis to post ecdysis.Comp. Bioahem. Physiol. 54A:55-60.

Passano, L.M. 1960. Molting and its control. In The Physiology,wfCmstaoea, ed. T. Waterman, Vol. I, pp. 473-536. New York: AcademicPress.

Skinner, D.M. 1968. Isolation and characterization of ribosomal ribo-nucleic acid from the crustacean, Geeareinus late~alis. J. Zzp.Zool. 169:347-355.

Skinner, D.M., and D.E. Graham. 1972. Loss of limbs as a stimulus toecdysis in brachyura true crabs!, Biol. Bull. 143:222-233.

Warner, G.F. 1977, The Biology of Cx'ass. New York: Van blostrandReinhold Company. pp. 126-127,

Weis, J.S. 1976, Effects of environmental factors on regeneration andmolting in fiddler crabs. Biol. Bull. 150:152-162.

14

APPENDIX

The Stages of the Crab Molt Cycle from Warner, 1977!

Stage A. Newly molted

A!. The exoskeleton is a soft membrane. The legs are unable tosupport the body weight in water and the crab is inactive.Water absorption continues. Exocuticle mineralization begins.

The exoskeleton feels like parchment, The crab can supportits weight and move about. Water content stabilizes at about86 percent. Endocuticle deposition and mineralization begins.

A2.

Stage B. Recently molted

Bl. The exoskeleton is generally deformable without breaking.

Parts of the exoskeleton becomes rigid, e.g., the chelipeds{pinchers! now break rather' than bend when force is applied.Feeding may start.

B2.

Stage C. Intermolt

Cl.

The carapace is completely rigid. The branchiostegites, sternites,and walking legs are barely flexible and crack if bent. Tissuegrowth continues.

C2.

The whole exoskeleton is rigid but endocuticle {inner layerof the exoskeleton! mineralization may still continue, Theinner, membranous layer is not completed until the end of thissub-stage.

C3.

The exoskeleton is complete. The presence of the membranouslayer' can be judged by cracking and lifting a piece of thecarapace or breaking off the dactylus of a walking leg: themembranous layer should remain attached to the shell. Tissuegrowth is complete and metabolic reserves accumulate. Thewater content is 61 percent.

Cg.

Terminal anecdysis is distinguished by the membranous layeradhering closely to the rest of the exoskeleton. it is notdetectable except by histological microscopic structure oftissue! examination. Crabs are full grown and often show signsof age; the exoskeleton may be damaged and may support asessile epifauna.

CgT.

17

The carapace is almost completely rigid but the branchiostegites{gill chamber wall!, sternites {ventral surface!, and the walkinglegs are still flexible. This is the main per'iod of tissue growth.

Stage D. Premolt

The epidermis separates from the membranous layer and secretesa new epicuticle. New spines develop within the cores of oldones; they are very soft but may be seen if a dactylus Finalsection of a limb! is broken off and the tissue withdrawn.Reserves are mobilized and glycogen builds up in the epidermaltissues.

D!.

Dp.

This is the main period of old exoskeleton resorption and isgreat at particular sites, e.g., the epimeral lines to allowsplitting at ecdysis. Slight pressure on the epimeral lineresults in a precocious split,

D3.

Resorption is complete. The old exoskeleton splits along theepimeral lines and water uptake begins.

State E. Ecdysis.

The crab withdraws from the old skeleton and takes up waterrapidly.

18

New exocuticle secretions begin. The new spines are now firmand stand out from the tissue withdrawn from a broken dactylus.The old membranous layer degenerates to a gelatinous layer.Resorption of the old exoskeleton begins. Activity. is reducedand feeding stops as the crab loses its muscle insertions,