Assessment of depuration system and duration on gut evacuation rate and mortality of red swamp crawfish

Transcription

1 Ž. Aquculture Assessment of depurtion system nd durtion on gut evcution rte nd mortlity of red swmp crwfish W. Ry McClin ) Louisin Stte UniÕersity Agriculturl Center, Louisin Agriculturl Experiment Sttion, Rice Reserch Sttion, P.O. Box 1429, Crowley, LA , USA Accepted 19 November 1999 Abstrct Two depurtion, or purging, systems were exmined for their effect on survivl nd evcution rte of intestinl contents of the hindgut of crwfish Ž Procmbrus clrkii.. In the immersion system, crwfish were held in bskets suspended in the wter column nd subjected to profuse ertion nd low wter exchnge. Crwfish in the wter spry system were mintined in shllow pools Ž 1.3-cm deep wter. nd in constnt mist environment. Loding rte for ech system ws 14.5 kg crwfishrm 2 surfce re. Similr mortlity ws observed from the two systems nd verged 9% nd 12% for 24 nd 48 h of purging, respectively. Cnniblism occurred in both purge systems; however, the men net hindgut evcution rte for crwfish ws similr for the two systems nd verged 57%, 63%, 78%, nd 81% for 12-, 24-, 36-, nd 48-h purge durtions, respectively. Evcution efficiency fter 12 nd 24 h ws positively correlted with wter temperture. Of the totl mount of intestinl contents excreted during 48 h of purging, 70%, on verge, ws excreted within the first 12 h. Mortlity increses s purge durtion increses; therefore, the shortest nd most prcticl durtion tht results in product cceptble by the consumer will be the most cost effective. A 12-h Ž or overnight. durtion in well-mnged systems my be sufficient for most mrkets in Louisin. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Crwfish; Cryfish; Purging; Depurtion; Mortlity; Evcution ) Tel.: q ; fx: q Ž. E-mil ddress: rmcclin@gctr.lsu.edu W.R. McClin r00r$ - see front mtter q 2000 Elsevier Science B.V. All rights reserved. Ž. PII: S

2 268 ( ) W.R. McClinrAquculture Introduction Louisin Ž USA. hs thriving crwfish Ž Procmbrus clrkii nd P. zonngulus. production industry. During the seson, frm production from 44,500 h totled 16.4 million kg, which ws worth US$22.5 million. The nturl fishery of wild crwfish ccounted for n dditionl US$19 million ŽLouisin Coopertive Extension Service, Frm-rised crwfish re lso produced in other southern sttes of the US, lbeit in much smller quntities. The preferred wy to prepre crwfish for the consumer is to boil the whole niml in sesoned wter. The consumer then extrcts the bdominl met by hnd, which is lso the preferred method for eting crwfish in Europe mjor export mrket for Louisin s lrgest, most vluble crwfish. A portion of the nnul hrvest is lso commercilly processed for the bdominl met Ž Huner et l., To render more ppeling product for the whole-crwfish mrket, crwfish re sometimes plced in depurtion or purging systems for 1 or 2 dys. In these systems, crwfish re confined in wter or very humid environments nd food is withheld. This process clens the exoskeleton of mud nd debris, nd elimintes or gretly reduces digest in the hindgut Ž intestine., which mny consumers find unppeling. When the exoskeleton is removed Ž peeled. from the bdomen, the hindgut, which lies dorslly long the bdomen, is exposed. The full, drk colored intestine of n unpurged crwfish conspicuously contrsts with the light colored met. The exposed contents of the full intestine re prticulrly offensive if the intestinl wll is ruptured during peeling, contminting the met with fecl mteril. Purging mitigtes this unppeling spect of crwfish consumption. The intestine of fully purged crwfish is smller, trnslucent, nd much less conspicuous. Purging lso serves to remove ingest from the foregut nd clen the brnchil chmber of grit nd mud, which contminte the cooking wter when multiple btches of crwfish re boiled. In the southern USA, mny lypeople improperly define purging s plcing crwfish in tub of wter with g of sodium chloride for few minutes. This does little to remove the contents of the intestine nd is simply little more thn cursory wsh. The slt hs little effect. Purging, to the extent tht intestinl contents re significntly reduced, requires dditionl time. Some people, especilly Louisinins, who hve been eting crwfish for mny yers, re ccustomed to non-purged crwfish nd do not find them objectionble; nonetheless, mny would probbly prefer purged product if the higher costs were resonble. Although the current mrket for purged crwfish is reltively smll due to lck of public wreness nd price differences Ž 15 25% higher., purging hs contributed to repet sles nd loylty to certin producers or distributors ŽHby nd Younger, 1989; Avery nd Lorio, Promotions of purged crwfish in non-trditionl locles hve helped to foster new mrkets. At one time, purging ws lso thought to increse shelf life of crwfish held in cooler until cooking ŽHby nd Younger, 1989; Huner nd Brr, 1991., but this clim hs been refuted Ž McClin, However, purging my benefit other spects of crwfish processing, such s lower bcteril counts in peeled bdominl met Ž Treece,

3 ( ) W.R. McClinrAquculture Huner et l. Ž review some of the commercil depurtion systems tht cn be clssified s either immersion types Ž crwfish re totlly immersed in wter. or spry types Ž non-inundted crwfish exposed to wter spry or mist.. Few studies hve evluted the purging process ŽLwson nd Drpcho, 1989; Lwson et l., 1990; McClin, 1994; McClin et l., 1994., nd the scope nd findings of those studies were limited. Mny spects of crwfish depurtion remin undocumented. This study ws conducted to evlute severl spects of the purging process. The min objectives were to exmine the efficiency t which crwfish evcute the contents of the hindgut under typicl purging conditions nd to compre mortlity nd the efficiency of gut evcution in two types of depurtion systems t common loding rte. Evcution efficiency ws exmined t 12-h intervls, in lieu of 24-h intervls commonly used in the industry, to obtin more ccurte ssessments of gut evcution rte. 2. Mterils nd methods Red swmp crwfish Ž P. clrkii., the most bundnt commercil species, were used for this study nd were produced t the Louisin Agriculturl Experiment Sttion s Rice Reserch Sttion, Crowley, LA. During 1997 nd 1998, crwfish were hrvested Ž h. from commercil-type rice-field ponds using bited wire mesh trps. They were immeditely plced into hrd plstic crtes nd put into one of two depurtion systems within 2 h fter cpture. Crwfish hrvested on four dtes ŽApril to June. in 1997 were subjected to n immersion system of depurtion, nd those hrvested on seven dtes Ž Februry to My. in 1998 were depurted in immersion or spry type systems. The 11 test periods encompssed wide rry of environmentl nd biologicl conditions typicl of the crwfish hrvest seson in Louisin. In the immersion system crwfish were fully immersed in wter under conditions of profuse ertion nd low rte of wter exchnge. The spry system consisted of non-immersion spry with high rte of wter exchnge. The immersion system Ž Fig. 1. ws smller version of commercil type, developed by the uthor in 1981 nd subsequently dopted by mny tht commercilly purge crwfish. It consists of n oblong, convex-bottom tnk Ž 2570 l. with suspended bskets tht re plced crosswise inside the tnk nd hold crwfish in the wter column. The tnk is equipped with solid prtition in the center to provide two similr, but seprte, units supporting six bskets ech. The bsket frmes re semi-circulr in shpe nd mde from luminum tubing covered with perforted luminum sheets Ž 4.8-mm mesh.. Crwfish cling to ll surfces of the bskets nd occupy the entire submerged surfce re Ž1.2 m 2. within three-dimensionl spce. A loding rte of 14.5 kg crwfishrm 2 surfce re ws chosen to obtin mximum use of vilble surfces nd ws within the kgrm 2 rnge of densities commonly used in commercil purging systems ŽLwson nd Drpcho, Profuse supplementl ertion ws supplied vi rotry vne compressor nd diffused through two 15.2-cm irstones plced directly beneth ech bsket. Flow-through wter ws dded to ech hlf of the tnk t rte of 0.6 lrmin. The tnk ws clened nd filled with clen wter prior to ech test dte. The spry system consisted of twenty-two, 38-l plstic continers Žbottom surfce res0.076 m 2.. Ech continer ws equipped with center drin tht mintined 1.27

4 270 ( ) W.R. McClinrAquculture Fig. 1. This immersion system for purging crwfish utilizes low wter exchnge nd profuse ertion nd is designed with hinged bskets for efficient delivery of the wshed nd purged product. cm of stnding wter nd spry nozzle 51 cm bove the bottom. Crwfish were prtilly immersed with only the lower one-hlf of the niml under wter. A fine mist of wter Ž 0.3 lrmin. ws continuously directed into the continer, resulting in high Ž 2 humidity nd stedy exchnge of wter. The crwfish loding rte 14.5 kgrm re. ws the sme s tht of the immersion system; however, crwfish were confined to single plne Ž bottom. in this system. Both systems used common source of well wter filtered through commercil wter softening system. The qulity of wter from this source ws previously determined to be suitble for purging crwfish; influent nd effluent chrcteristics of the wter re presented in McClin Ž nd McClin et l. Ž Wter temperture during this study ws monitored in the ponds t hrvest Ž dt loggers. nd in the depurtion systems during purging Ž minimumrmximum thermometers.. Rndomly selected crwfish were llocted Ž t the prescribed loding rtes. to two bskets Ž one in ech tnk hlf. of the immersion system for ech test period in In 1998, crwfish were ssigned to eight bskets Ž four in ech tnk hlf. of the immersion system nd to 22 continers of the spry system t ech test period. Smples of crwfish were removed from the bskets every 12 h in 1997 for hindgut content weight, nd mortlity ws ssessed for the reminder of the crwfish fter 48 h. In 1998, two of the bskets in the immersion system were exclusively used for 12-h smplings for gut content, nd three other bskets were ech emptied t 24 nd 48 h to determine mortlity. In the spry system, due to the reltively few crwfish per continer nd the potentil impct of decresing density on subsequent results, smples of crwfish were tken for gut content weight from two different continers t ech 12-h intervl. Seven dditionl continers were ech ssyed for crwfish mortlity fter 24 nd 48 h.

5 ( ) W.R. McClinrAquculture For ssessment of hindgut content weight, five mture nd five immture crwfish were collected prior to depurtion nd then from designted replictes t ech 12-h smple period. Equl numbers of mles nd femles were collected when possible. Crwfish were immeditely nd individully frozen Ž y188c. nd t ltter dte thwed, weighed, nd dissected. The intestine, or hindgut, ws seprted t its junction to the midgut nd left ttched to the nus. The telson, with intct nus nd ttched hindgut, ws removed from the bdomen nd centered over pre-weighed luminum pn. Contents of the hindgut were collected in the pn by flushing the gut with 3 ml of distilled wter dispensed from smll syringe through the nus. Gut contents from ech of the five mture nd five immture crwfish were pooled, nd dry weight ws recorded fter drying overnight t 758C. Dry gut content weight ws computed s percent of whole wet crwfish weight, wet bdominl muscle weight, nd dry bdominl muscle weight. Gut evcution rte ws determined s the men percentge loss for ech 12-h durtion, nd net incrementl loss ws defined s the percent of the men totl loss Ž fter 48 h. tht occurred t ech 12-h increment. Mortlity tht occurred during purging ws determined by closely exmining every niml fter removl from designted continers in ech purge system. Sexul mturity of ded nd surviving crwfish ws lso determined s described by McClin Ž The experimentl pproch consisted of rndomized incomplete block design with test dte s the blocking fctor. Dt were nlyzed with the Generl Liner Model procedure in fctoril rrngement of tretments Ž system nd time intervl. using the Micro SAS Sttisticl Softwre System ŽSttisticl Anlysis Systems version 6.10, SAS Institute, Cry, NC.. Min effects were tested for interctions nd nlyzed independently if no significnt interction Ž P F occurred. For the independent nlyses, if significnt differences were present, Duncn s multiple rnge test ws used to seprte tretment mens t P F The reltionship between wter temperture nd gut evcution rte Ž or crwfish mortlity. ws determined by simple liner correltion nlysis. 3. Results About 950 kg of crwfish Ž ) 35,000 individuls. were exmined for purge-relted mortlity over the 2-yer period of investigtion. The percentge of crwfish dying during purging for ech yer, nd the proportion of immture crwfish in the ctch nd those tht died during purging re depicted in Tble 1. The mturity sttus of substntil portion of ded crwfish could not be identified in 1998 s result of cnniblism. Miniml unidentifible remins were found in The dt indicte tht mortlity incresed with n increse in durtion of purging, with greter incidence of deth mong immture crwfish. Mortlity ws highly vrible with respect to test period Ž Tble 2., nd no trend reltive to hrvest period or temperture ws observed. Mortlity fter 24 nd 48 h of purging verged 9% nd 12%, respectively. Although results were highly vrible, no significnt differences due to purge system type were observed for mortlity or composition Žregrding identifible or unidentifible mturity sttus. of the ded crwfish Ž Tble 3..

6 272 ( ) W.R. McClinrAquculture Tble 1 Men percent mturity nd mortlity for crwfish Ž ns35,264. subjected to purging Hour Percent Percent Percent Percent immture of ctch mortlity immture of totl ded unidentifible of totl ded About 1500 crwfish were dissected for determintion of hindgut content. The verge mount of hindgut contents Ž dry weight bsis. voided during purging, bsed on percentge of whole crwfish weight, generlly declined with time Ž Tble 2.. The mximum net evcution efficiency ws - 90%, nd crwfish verged 57, 63, 78, nd 81% evcution of the hindgut fter 12, 24, 36, nd 48 h of purging, respectively. Of the 11 evlution period verges, only one men net evcution pek occurred within the first 12 h of purging Ž 26 My 1998.; no peks occurred t 24 h, four occurred t 36 h, nd six occurred fter 48 h of purging. Men percent evcution for ech 12-h increment ws generlly positively correlted with wter temperture t hrvest nd during purging Ž minimum, mximum, nd medin. for seprte correltions; temperture t hrvest hd the higher correltions, which were only significnt t the 12-h Ž rs0.705; Ps Tble 2 Wter temperture Ž 8C. t hrvest nd during purging, men Ž "SD. percent net evcution of hindgut contents, nd percent mortlity for ech test period Dte Temperture Percent gut evcution Percent mortlity Hrvest Purge 12 h 24 h 36 h 48 h 24 h 48 h ŽMin Mx. 10 April Ž Ž Ž Ž April Ž Ž Ž Ž My Ž Ž Ž Ž June Ž Ž Ž Ž Februry Ž Ž Ž Ž Mrch Ž Ž Ž Ž Mr ch Ž Ž Ž Ž April Ž Ž Ž Ž April Ž Ž Ž Ž My Ž Ž Ž Ž My Ž Ž Ž Ž Averge Not determined.

7 ( ) W.R. McClinrAquculture Tble 3 Response vlues for crwfish purged in either spry nd submerged systems for 12-, 24-, 36-, or 48-h durtions during Mens followed by superscripts were significntly different, nd other men comprisons within ctegory by durtion were not significntly different Ž P ) h 24 h 36 h 48 h Percent mortlity Spry 9 13 Immersion 9 18 Percent immture of ded Spry Immersion Percent unidentifible of ded Spry 8 19 Immersion Percent gut eõcution Spry B Immersion A Not determined. nd 24-h Ž r s 0.870; P s durtions. The correltion coefficients Ž r. for the 36- nd 48-h periods were Ž P s nd y0.433 Ž P s , respectively. Net gut evcution rte ws slightly ffected by purge system type Ž Tble 3.. Only t the 36-h period ws there significnt difference Ž P s 0.03., with crwfish in the immersion system hving the higher rte. The most notble difference between the two systems is tht the men pek in net gut evcution occurred t 36 h in the immersion system nd t 48 h in the spry system. Becuse there ws generl lck of differences due to purge system type nd with no significnt interction between system nd purge durtion, dt were pooled with regrd to computtions nd nlyses of hindgut content s percent of tissue weights Ž Tble 4.. Overll, the purging process resulted in significnt reduction in the percentge of contents of the hindgut, lthough the reductions t ech 12-h increment were not lwys significnt Ž P) There were smll differences nd no obvious trend due to mturity. Approximtely 70% of the net totl excrement loss occurred during the first 12 h, bout 77% occurred within 24 h of purging, nd 97% occurred within 36 h of purging Ž Tble Discussion It is widely ccepted tht purging, especilly the immersion process, is effective in clening the exterior Ž nd brnchil chmber. of crwfish ŽHby nd Younger, 1989; Lwson nd Drpcho, 1989; Huner nd Brr, Although clenliness of the exterior ws not ssessed in the present study, the results indicte tht both spry nd immersion system of purging re eqully effective in clering digest from the hindgut.

8 274 Tble 4 Men hindgut content weight Ž dry. s percent of wet whole crwfish weight, wet bdominl muscle weight, nd dry bdominl muscle weight before nd fter purging. Net increment loss Ž for ech reltive tissue comprison. ws clculted s percent of the net totl content loss tht occurred t ech 12-h increment of purge durtion. Mens followed by the sme superscript within column were not significntly different Ž P )0.05. Hour Bsed on wet crwfish Bsed on wet bdominl muscle Bsed on dry bdominl muscle Percent dry Net increment loss Percent dry Net increment loss Percent dry Net increment loss gut content s percent of totl loss gut content s percent of totl loss gut content s percent of totl loss A A A B B B B B B C C C C C C Men hindgut content weight Ž s percent of wet nd dry bdominl weights. from mture crwfish fter 48 h of purging ws significntly Ž P greter thn from immture crwfish. Men comprisons bsed on crwfish mturity for other 12-h increments nd reltive to wet crwfish weight were not significntly different. W.R. McClinrAquculture 186 ( 2000 )

9 ( ) W.R. McClinrAquculture Few differences between the two purge system types were observed reltive to gut evcution rtes nd mortlity t the loding rtes tested. The spry system used in this study mintined shllow lyer of wter in which the crwfish resided. Personl experience nd necdotl observtion in the use of spry systems tht did not llow for stnding wter suggest tht mortlity of crwfish fter 24 h my be higher thn tht in well-mintined immersion systems. Lwson nd Drpcho Ž reported tht crwfish purged eqully s well in spry nd immersion Ž flow-through. systems, lthough they did not stte whether stnding wter ws present in the spry system. They further reported possible trend of lower mortlity in the spry system, but there were no significnt differences. Mortlity during purging is mjor fctor tht leds to higher prices for the product ndror directly impcts producer profits. In this study, survivl ws significntly ffected by purge durtion, regrdless of system type. Mortlity fter 48 h of purging verged 63% higher thn tht fter 24 h, in 1998 Ž Tble 1.. Although mortlity ws not mesured t the 12- nd 36-h intervl, it is suspected tht mortlity increses s purge durtion increses for ny given set of conditions. In other reports, purge-relted mortlities fter 24 h Ž lbeit highly vrible. verged - 10% in one study ŽMcClin et l., nd 11.6% in nother study Ž McClin, Lwson nd Bskin Ž reported men deth loss of 24% for crwfish purged for 5 dys t comprble loding rte. Crwfish mintined in refrigerted storge for the sme 5 dys in tht study verged only 3% mortlity. Lwson et l. Ž reported significnt increse in mortlity s the loding rte incresed from 4.9 to 34.1 kgrm 2 in wter spry system. Results of this study corroborted erlier findings ŽMcClin, 1994; McClin et l., tht showed much higher mortlity of immture crwfish. Immture crwfish re likely to be more susceptible to purge-relted mortlity due to higher proportions of prend post-molt individuls, thinner exoskeletons, nd generlly smller sizes. Lower mortlity fter 48 h of purging during 1997 my be the result of lower proportion of immture crwfish composing the ctch. Acute outbreks of vibriosis my lso be the cuse for some observnces of high mortlity mong crwfish during purging Ž Thune et l., 1991., especilly with the red swmp crwfish. P. clrkii ppers to be more sensitive to the Vibrio orgnism thn P. zonngulus Ž Huner, Mny other fctors, both before Že.g., stress in trps, hndling prctices, nd length of time out of the wter. nd during purging Že.g., loding rtes, size vrition, nd wter qulity., re likely to influence survivl nd should be investigted further. The depurtion process ws not completely effective in voiding ll contents from the hindgut of crwfish in this study. The gut ppered to be completely voided in mny individuls, while vrible mounts remined in few individuls, even fter 48 h. Lwson et l. Ž reported tht the intestines of crwfish were observed to be completely free of fecl mtter fter 40 h of purging; however, reltively few crwfish were exmined in tht study, nd evcution efficiency ws determined by visul observtion only. The level of cnniblism ws not discussed in other purging reports, but for this study cnniblism ws pprent in both purge systems nd probbly contributed to residul contents in the gut, especilly fter long purge durtions. A

10 276 ( ) W.R. McClinrAquculture higher incidence of cnniblism ws pprent fter 36 nd 48 h, s evidenced by lrger percentge of unidentifible remins Ž Tble 1.. Cnniblism ws lso probble cuse for peks of evcution prior to the 48-h intervl for certin dtes Ž Tble 2.. Bsed on moisture content of 31% Ž unpublished dt, 200 crwfish., the wet gut content of unpurged crwfish represents less thn 2% of the wet bdominl muscle weight. However, the drk, full intestine is conspicuous nd, lthough it is normlly Fig. 2. Exposed intestine Ž hindgut. of cooked whole crwfish nd bdominl muscle from crwfish tht were either purged for 24 h Ž right. or not purged Ž left. prior to cooking. Note the fullness nd conspicuous chrcteristic of the intestine in the non-purged specimens.

11 ( ) W.R. McClinrAquculture discrded, it cn be unppeling to mny consumers. Wheres, on verge, some gut content remins fter purging, the exposed bdomens of non-purged crwfish re much less ppeling thn those of purged specimens Ž Fig. 2.. Most Ž ) 70%. of the net totl gut contents voided were evcuted during the first 12 h of purging, especilly t the higher tempertures, when most of the nnul hrvest occurs. In ddition, the lowest mortlity presumbly occurred t 12 h, representing the lowest economic loss for producer who employs purging. Only nother 7% of the gut content were evcuted fter n dditionl 12 h of purging, when mortlities re likely to increse substntilly. Most of the benefits of clening the exterior of crwfish should lso be relized within the first 12 h of purging. Therefore, ssuming consumer cceptnce, 12-h purging durtion is recommended, followed by storge in refrigerted coolers if necessry. Mortlity is reduced when crwfish re properly held in refrigerted storge rther thn in purging systems Ž Lwson nd Bskin, 1985; McClin, In summry, the immersion nd spry depurtion processes were effective in significntly reducing the content of the hindgut, nd evcution rte nd mortlities for both systems were comprble. Becuse purge-relted mortlities increse with time, purge durtion should be held to minimum. Purging to increse product cceptnce does exct cost by t lest s much s the percentge of mortlities. Additionlly, one should consider the dded cost ssocited with cpitl expenditures nd operting expenses when mrketing or purchsing purged crwfish. Cost nd energy fctors were not considered in this reserch, but findings tht the different purge systems produced similr outcomes under the conditions investigted, should lend support to those who will decide which system is the most efficient in terms of cpitl expenditure, operting cost, energy requirement, spce, nd other efficcy issues. More effort needs to be directed towrd determining the miniml purge durtion Ž i.e., level of gut evcution. tht is cceptble to the consumer nd other optimum operting conditions, such s rtes of loding, flow, nd ertion. Acknowledgements Apprecition is extended to John Sonnier for his invluble ssistnce with dt collection nd processing. Thnks re lso extended to Drs. Robert Romire nd Jy Huner for their criticl reviews nd constructive comments. This work ws supported by the Louisin Agriculturl Experiment Sttion nd pproved for publiction by the Director, Louisin Agriculturl Experiment Sttion, s mnuscript number References Avery, J., Lorio, W., Crwfish Production Mnul. Publ. 2637, Louisin Coopertive Extension Service, Bton Rouge, LA, USA, 38 pp. Hby, M.G., Younger, W.R., Texs crwfish quculture: n nlysis of producer survey focusing on current industry prctices, conditions, mrketing plns nd ides for the future. Texs Mrine Advisory Service, Texs Agriculturl Extension Service, College Sttion, TX, USA, 36 pp.

12 278 ( ) W.R. McClinrAquculture Huner, J.V., Ecologicl observtions of red swmp cryfish, Procmbrus clrkii Ž Girrd, 1852., nd white river cryfish, Procmbrus zonngulus Ž Hobbs nd Hobbs 1990., s regrds their cultivtion in erthen ponds. Freshwter Cryfish 10, Huner, J.V., Brr, J.E., Red Swmp Crwfish: Biology nd Exploittion. The Louisin Se Grnt College Progrm, Center for Wetlnd Resources, Louisin Stte University, Bton Rouge, LA, USA, 128 pp. Ž Revised.. Huner, J.V., Moody, M., Thune, R., Cultivtion of freshwter cryfishes in North Americ. In: Huner, J.V. Ž Ed.., Freshwter Cryfish Aquculture in North Americ, Europe, nd Austrli. Fmilies Astcide, Cmbride, nd Prstcide. Hworth Press, Binghmton, NY, pp Lwson, T.B., Bskin, G.R., Crwfish holding nd purging systems. ASAE Pper No Pper presented t the 1985 Summer Meeting of Am. Soc. Agric. Eng., Est Lnsing, MI, June ASAE Pper No Lwson, T.B., Drpcho, C.M., A comprison of three crwfish purging tretments. Aquculturl Engineering 8, Lwson, T.B., Lll, H., Romire, R.P., Purging crwfish in wter spry system. Journl of Shellfish Reserch 9, Louisin Coopertive Extension Service, Louisin Summry of Agriculture nd Nturl Resources. Louisin Stte University Agriculturl Center, Bton Rouge, LA, USA, 318 pp. McClin, W.R., Evlution of grding, depurtion, nd storge time on crwfish mortlity during cold storge. Journl of Shellfish Reserch 13 Ž. 1, McClin, W.R., Tylor, K.R., Sonnier, J.J., Effects of wter source on crwfish mortlity during purging. In: 86th Annul Reserch Report, Rice Reserch Sttion, Louisin Stte University Agriculturl Center, Louisin Agriculturl Experiment Sttion, Bton Rouge, LA, USA. Rice Reserch Sttion, Louisin Stte University Agriculturl Center, Louisin Agriculturl Experiment Sttion, Bton Rouge, LA, USA, pp Thune, R.L., Hwke, J.P., Siebling, J.S., Vibriosis in the red swmp cryfish, Procmbrus clrkii. Journl of Aqutic Animl Helth 3, Treece, G.D., Brine freezing crwfish. In: Proceedings of the 1984 Crwfish Production nd Mrketing Workshop. Texs Agriculture Extension Service, By City, Texs, USA, pp