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CYSTER I'IORTALITY CCNFEIIENCE

January 2A-22, 7959

RUTGERS, THT STATS UNIVERSITYNEl'l BRUNSI'rICK' NEI'I JERSEY

In cooperation \rithBranch of Conrmercial FisheriesU. S. Fish & I{ildlife Service.

SLIMi'#.RY OT' CONFERENCE

Enc losure : 1-2-

Topics for DiscussionAttendance

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-2-

OYSTER I.IORTALITY CONFERENCE

January 20-22, 1959

Rutgers, The State UniversityNew Brunsr.rick, New Jersey

TOPICS FCR DISCUSSION

I. PATTERNS OF IYSTER I\:ORT-r';LITY:

l',. !/-Spring }lortality-Delaruare Bay Staff. N,J.C.R.L. includingB. 5B-Fa1I i'lortatity-Deiaware Bay MeDermott' Intensity, scope, timing, saqilingC. MorEalities in Delar.rare l.,laters ShusterD. l'lorLalities in Lon3 Islenc! Sound NeQsonE. Canadian i'iortalities LogieF. Ilortalities in Chincotea3ue Area Sielin3-Carver-EngIeG. l'lortalities in Chesapeake Bay Andreivs-Beaven

II. CAUSA.TIVE AGENTS :

A. DermocystidiumB. Examinations for parasites

Hexamita, Nsrn€igopsis, Ci liateC. Bacrerial Stud iesD. Tl-:e ttner,r orqanismrr

And rer,;s -Krs1g ] q - I'ly rheStauber

Loi ie-Ade IsonS tauber-Ne I son-Haski n

I, Description of sEa,ses,Demonstrat i ons

2. Inoeulation experiments Eeng-Canzonier7. Culture observations Itlyrhe-Logie|.1. Tray studies-Cape Shore Haskin

III. \{ORK TO BE DONE:

A. i^tri th Agents:Identification, culture, limitinq fact.ors

B. l.lith Hosr:Tran.sfer of inf ecEionsResistance sCudies

C. ilith Industry:Development of Resistant StrainsImporration Policy

-?-

OYSTER MORTALITY CONFERENCE

January 20-22, L959

RBtgers, The State UniversityNew Brunswiek, New Jersey

MEMBERS:

L. l'1. ADELSON DEPT. OF ZOOLOGY, RUTGERS UNIV,T NE't BRUNS.

rI. D. .rillDRElfS OYSTER BIOLCGIST, VIRGINIA FISH LAB., GLOUCESTER PT.,VIRGINIA

G. FR.::NCIS BEaTVEN SI{ELLFISH BI'ILOGIST, CHEASAPEAKE BIOLOGICAL LABOMTORY'soLoMoNS, ID.

1,1. J. CAIIZONIITR DEPT. OF ZOOLOGY, RUTGERS UNIV.; NEI{ BRUNSI"rICK

TCI'I Ci'TRVER U.S.F. & I{. S. L,^.8, FRANKLIN CITY, VIRGINIA

J,1,MES B. DUR'l.iiD DEPT. CF ZOOLOGY, I].UTGERS UNIV., CAI'IDEN, N.J.

JrrrMES B. INGLE CHIEF, U.S. FISH &'iILDLIFE SERVICE, BUR, COMI"I. FISH,ANN;IPOLIS, l'ID.

suNG YEN FENG DEPT. CF ZOOLOGY, RUTGERS UNIV., NEr^' BRUNS.

JOHN B. CLUDE CllIEE, BR,INCH OF SHELL FISHERIES, BUR. COI'JM. FISH,

"iASHINGTON, D.C.

H^RCLD H. HASKTN DEPT. OF ZCOLOGY) RUTGERS UNIV., NEW BRUNS.

DEXTER iLriVEN OYSTER BIOLOGIST, VIRGINIA FISH HB., CLOUCESTER PT.,VIRGINIA

H/,RRy P. JIFFRTES DEPT. CF ZOCLOGY, RUTGERS UNIV.T NE\^.r BBUNS,

R. F.. LOGIE FTSHER.IES RES, BO..,RD OF CANADA, ELLERSLIE, p.E.I.

JOHN MCDERMOTT DEPT. OF BI,LCGY, FRANKLIN & MARSHALL COLLEGE.L;T,NCASTERTPENNSYLVANIA

JOHN L. MYHRE RESEARCH ASSISTANT' N.J.O.R.L., BMLVET NEIrt JERSEY

THURLOI': C. NELSON N.J. DIVISI]N CF SHELL FISHEFIES

CHRISTCPHER F.ILEY DIRECTOR, N.J. DIVISION OF SHELL FISI{ERIES

RUDOLPH SCHELTEI'IA RESEARCH ASSOC., N.J. OYSTER RESETRCH LAB.

CAR,L !F.'iSIIIJ&IEER:-JR. UNIV, OF DELAI^IAR.E, DIRECTOR, MARINE LABS.

FRED i'J. SIELING MD. DEP?. RESEARCE EDUCATICN, SNCl,l HILL, MD.

LESLIE A. STpUBER DEPT, OF ZOOLOGY, RUTGERS UNIV., NEIiI BRUNS,

-l] -PATTERNS OF OYSTER MORTALITY

A. Pelaware Bay.1957-58. Haskin and staff New Jersey oysrer Research Laboratory

In the six-week period from mld-Apri1 to late May 1957, oysters diedrapidly in extensive areas of the New Jersey planted oyst.er grounds. Junesampling indicated that the kiIl was centered on the'rShoal Sand Bar and up-per Deept'raEer grou1ds wlth 6enerally decreasing intensity of ki11 as distancefrom this eenter increased. One Bar grourid had 85% till and several had about70% 8i11. The kill dropped off Eo 35i in rhe Ledge, Sourhwesr Line and LowerDeePwater areas. No appreciable mortalities occurred on Miah I'4au11 groundsor in Section A - the easternmqq,t portion of the planted areas '- frir on eheNatural Seed Beds.

On the planted grounds at this tlme were oysters from a varieLy of sources.Approximately half a million bushels of seed oysters from the Natural Bedshad been p1-anted in }{ay L956. According to the best information availableEhere was probably a nn.rch larger quantity of James River stock on the grounds,replanted from Lower Chesapeake Bay grounds. Few grounds of Virginia rtbrushtf(oyster from the Virginia seaside) r.rere planted. There was no apparent differ-ence in suscepEibilitv of these various stocks. James Rivers and Native Bayson adjoining grounds l{ere equally hard hit. There r.'as a suggestion that theVirginia f'brushrf was less hard hit, but there were not enough grounds of 'rbrushttto be sure of this.

Various grounds vrere sampled perioCically follorving this sprlng mortality,providing some evidence for additional ki11 in the fall of 1957 and, spring of1958. Stocks of oysters were 1or., hot'ever, and virtually all grounds r,rere t,run,tby the planters in the L957-58 marl<et season. Apparently rhe survivors of theL957 uill and rhe rvinrer of 1958-58 suffered an addirionar 30-ho% loss in rhespring of 1958.

In May 1958 apProximately h5O t,housand bushels of seed oysrers from theNatural Beds were ag6,in planEed. By September these v:ere shotring an unu3ualdeath rate' lictle or no sheil growth and apparently r,rere not feeding as in-dicated by stomach examinations and laek of style. By December total mort.al-ities on the 1958 plants ranged irom l+O-60%. Excluding drill-kill, deathef rom unknolrn causes, presumably an epi.deni.c dtsease, ranged ftom 25-hi)"/,,

The 1958-fa11 mortality differed from the 1957-spring kill in Ehat, inthe former, the ki11 rvas more uniform over the entj.re planted grounc]s and ex-tended to the Natural Seed Beds, as far up Bay as the I'Iiddle (above Ship John).Assuming that an infectious agent caused both, it rvould appear that the in-fection started in the Bar-Shoal Sand areas of heavlest oyster plantings andEhen spread rapidly to uniform infeetion over the entireplanEed area and lowerNatural Seed Beds.

B* Mortalities in State of Delaware i.laters. Shuster

The mortality data reported here are based onthe State pl-anted 8-10 thousand bushels of oystersas a sparirning stock. ht,[gn checked in AugusE 1957

spot checks. ln L)lS-gl ton the Rtdge (a seed bdd)

they r+ere blvin= rvell. In

L.

-5-

March 1958 ttre'i}laware SheIIfish Conrmlssion reported these as 't100% dead."Fresh-r,rater ki11 roas suspected, but this seems unllkely slnce no appreciablefresh-water kilI occurred at this time on New Jersey seed beds in much fresher\n'aters. The Delarvare Industry first publicly reporEed exEensive kills in latesummer and in September 1958. Four inspection trips were then made by theDelaroare I'{arine LaboraEory. T66 of these to Rehohoth Bay - Indian River area(i0,000 acres) indicated that Cape Shore set prantld here in 1957 r.ras about

7O% dead. Reports of ?0-90% mortality r,rere investi8aEed on t\^lo ttips toDelar',are Bay beds off Borvers Beach; on soft,-bottom beds roith nnrch hydroid andborin- spon[e, mortaliEy averaged fA'/,. Virginia 'tbrush" planted in spring off958 in the liispillion River area was l-iving sel1i tn the"i !fuiderhtll Rtter e*eait r,ras h07 dead.

This yearts production of oyst,ers r'ras estimated at not over 70r000 bushelsin contrast to 8001000 bushels for last year.

MortaLities in Lond Island Sound,4'reas,

In the absence of Dr. Loosanoff, Dr. Nelson reported on the frarrrentaryinformation available on recent Long Island Sound mortalities. In November '-

of. L95Q J. R. Nelson reported a loss of about three-quarters of his oystersf o1lor"'ing the rrhurricanerr r.:hich moved oysters in depEhs of rrater up to 50 f eet.In late summer of 1953, B0% of t.ire oysters on Fireplace 3round in GardenersrBay died suddenly. This mortality has never been explained. At this pointDr. Nelson emphasized the importance of considerin3 possible multiplieity offactors in such mortaliEies. For exarrple it may be an oversirnplification tothink of a causative agent r.rithout considering factors r".'hlch at the same timelor.rer host resist,ance, such as poor f ood conditions, smothering by storm-moved sediment.s etc.

Also about L95) Frank I'i. Flowers & Sons reported unexplained heavy mor-talities of market stocks in Oyster Bay. These mcrtallEies follorved shortlyple.ntin3 of oysters frorn the lower Hudson River.

Canadian,.Oys-ter Mortalities. Logie

Dr. Logie first reviewed the operations of the industry ln the SE. Lawrenceareas, pointing out that oyster product,ion ia ;enerally limited to the raarminner circle around Prince Edrrard Island. Peak production is about 15Or0O0bushels of seed stocli ior the entire area ro,ith relative production for i'trovaScotia, Prince Edward Isiand and Neru Brunsr,'ick in the proportions of li 22 2r'..The oyster-producin;: roate-r$ are ice covered from about mid-November Eo sometimein }iay. Setting is irregular because of 1or,r summer temperatureso, Sil.t' .

depostions in the rives is another criEical probl.em and limits oyst,er cultureto the mouths of estuaries.

In 1915 heavy mortalities occurred on oyster grounds in }lalpeque Bay onP.E.I. These r,rere not invesEi;zated until Dr. Needler arrived on the groundabout 1929. ReporEs of events of the intervenin. 1&-years are based thereforeon accounts oi 3rowers. In lplll some oysters from Ccnnecticut ruere plantedin Malpeque Bay by the Blue Points Company. Tire mortalities began in 1915and fanned out from the areas of this plantin3, Eventually morEalities of9O-95y" occurred in all oyster populations on the Island. AI1 transfers of

D.

-6-oysEers to the rnatnland roere embargoed and no mainrand outbreaks occurred un-tit 1955.

Dr. Needlerr ste::ting in Lg2g, gathered toqether quxu,lttq{,oysters anclstudied tl-re resistance Eo disease of -t.hese

anJ tneir spat, rn r\alpeque Bay,spat survivrl appeared aormar by Lgzg. The f ishefg recovered by L935. ;1.freroutbreak of the disease in Ehe Charlottetorun,^irea -in lgj6, resiLtant }lalpeque?:fiU

,.,+,:.:*?:::uO. rn rhis arear porducrion reached pre_disease tevels byL>-r ( ' rnls roolts prornisin3 f or an assisted-recovery. In the current mainlandoutbreaks in Nova scotia, the canadian government is movin: Iarge nuobers ofresisranr ovsrers Eo the epidemic areas, in an arr;;p;-;;";p;;;'recovery ofthe industry' rt has so far been shown that t,he transplanted, resist.anc sEocktuill spai':n in the new areas. Ilhether the spat is resistant, is noe yet kno,.rn.

ci'irsing concern at present are unusual unexplained mortatities in the heartof |ia1P"Oue Bay orzer the pest three rolnters. Oysters ha..re died at an approxi_mately constant rate of 302 per winier,Itiodel epidemies set r,p rvrtl'r susceptible stocr<s in epidemic r^:aters haveestabl"ished a cons jstant pettern of moital ity fcir tr.," ,,h"r0"0"" uiseaser,, asfo1lor+s: seed oysters first exposed in si:ring may or may not die )n the firstwinter' rn ti-:e folloruing'rumne;, mortalities continuing-tc the fali-freeze-upvri11 kilL \o-l+5%; in the seconc winrer anrl spring anotlrer uo-u5"a tlie ana bylate surnmer total mortalities tuil1 be "l,o"t

poi. rn folicwing yea::s mortalitiescontinue unti I onLy 1-5"L of the oysters sur'ive. rn sr-rmmaryr".ppr.rimat.e annualand cumulative rnortalities are:/.NNUAL

1 sL- year -tr-2 nd 'year 4O-t+57"3 rd .year 80%4 ttr year 60-6525 tir year t+OL (?)5 rh year ?5% (?)

CUi.,U] . TIVE

-T-145"L

90"L>> /.

This indicates the peak mortality in the 3rd year after exposure.rn the discussion Dr. Logi.e brough.t out the point that there has been nosin31e def inite symPtom of I'ia1peque disease, specif ically, yerlor,r pusrulesare not characteristic.

E. Chineoteague.i,iortalities. Irg.r e, !iel in;., Carver.

En3le - introduced this sccEion, pointing ou:& l.'ilffi Serviee in arrangin3 for the coll.ectionoyster :rortal i ty in I95S and their shipmenE to Nerv

:he role oi the U. S. Fishof samples from areas ofJersey for examination.

SielinJ - revier'red the recent history of the chincoteague area with.respecE to oys ter mortal i t i es as f oil lor,:s :

19.15'\6 l:*.. morEalities associated r.:iEh decomposirion of heavy blanketof aLgae_probably r..qardhiella,

L9SZ - Another summer loss-followlng excessive a1gae.1958 - Heavy algae gror'rths r^rere carried out of Bay by a June,'northeaster.f*As an example of morEalities, 2 beds planted t^rith virginia saltsin 1957 had 3O% kill by lare sunrmer of 195g (not drilled). Onebed of 1958 plants had 5o% dead by late surmner. rr is esrimaredthat 1958 mortalities in loruer Chincorea3ue average about 50%.Some Chesapeake transplanrs (late rvinrer 5F_gB) aiso Cied" ?rvo

-7-groups of oysters brought up from Oyster, Virginia liere comparedi

Planted in Sinepuxent Bay: By fall was 46=50"/" dead and sur-viV,:fS !^rere poor.Planted in Assawoman Bay (IsLe of I{right) are healrhy endliving we11.

By r,ray of eorrelations iE v;as pointed out Ehat yee.rs 1il+5, l9l+5, L952,and 1958 r.,'ere all r.ret years r,uith excessirre rainfal1. For example, salinitiesin tlre cenEer of Chlncotealue Bay this year r^rere 18-19% as cornpared t;ith Lheusual 25 o/oo. Tl"re Chincoteague watershed is small (about 110 square miles)but is intensil.'e1y farmed. There is a small native oyster population elongthe marsh banks in the lor..rer.parr of the Bay.

One l.:ould expect normally up to 107 annual mortality Cue to unexplainedcauses.

Car.rer: r^rho has been r..rorl<lng cooperatively l.iit:1 Sieling in the loi,,erCtrinc@ie area pointed out that in the'Queenrs Sounc area mortalities,"vereabout. 50% r',ith about 5"1 due to drills. The ki11 is,very spotty, hor+ever,as shovrn by 2 adjoinin3 beds, one with 11% and tire second r,'itlr about. 5O'L l(i11,As of 16 December, exarninatioa of becls inCicated tl:aE Ehe hiLl r.:as dropping^ccUIL.

ehesapealie Bay Mortalities.

1. I'faryland - BeavenMarvland has no real dri1l problem, except in Tangier Sound where drills

can kill up to 100% of the oysters.

Various mortalities r,rere revier^red as fo11or,,s:

1.

2.

F.

r9t6 -t93z -

on T'.lesEern sl.ore of Bay-up to 8OZ rnortalities; no explanation.Little Choltanl< Ri.rer - investiqated by IruiEt and Bearren inearly,lu..ust. Hauls shor,red mortalities from L0-1C07. Beaven re-calls that up to 54"/, of the recenrly dead oysters still had meatsin Eh.e shel1. Death occurred on t.he shal1oi.r bars indicatini thetit ruas probably not due to oxyEen lackr This area required 8 yearsfor tl-:e bars to 66te bacl< into production.to date: The last ttuo r.:inter-kil1s have been about t57 instead,:rfthe usual 5%. l.latermen ascribe fhis to the harder \.rinters. InL957 - Poconoke Sound, i^.rith a htgh Dermoclzstidium incidence, hada 3n-j5% ki11 of oysters. In L95B - durin3 AugusE and Septernberhigh :-ki11s oecurred on deep bars - attributed to the lor.r oxygenlerrels r:hich existed for at least 2 r,,eeks wl-i. 1e temperatures irereat ?5oC or mcre.

1957 -

In LI're }iaryland portion oi Pocomoke Souncl tl"ie olsEermen eatch their oronspat locaIly. In the Virginia portions of the Sound, James River Seed arep lanted.

?. Virginia - .tndrerss,i,ndrer."'s d i scussed patterns of

largely on r,ray studies and mostly20oC transtionaL temperature, E,his

mortality in the lower Chesapeake basedin terms of DerrrocystiCium ki 11s. ;\t 3area h.as ! r.:arm rnonths, frorn 1 june to I

Novembern and 7 co{{ months. By 1 July temperatures usually reach 25oC.

Peal< mortalities occur 1n ,fugust and Ssplsmber in Erays, Field mor-Ealitles are usually about 1/3 less. Levels and patEern of mortaliiy are in-fluenced by source and ages of oysters. Infections butld up slor.rly in unin-fecEed seed oysters a.nd in the first 2 years kil1s are lor.r at 5-lO"/,,. Thekill builcis up in the lrd year and reaches a peal< in the 4th year,

The leve1s of ki 1l in trarTs over the last E years are given belora, i'hese...:ere all'.rith three anC four year-old oygters.

19s r1952t953t954

1 r'/1a'7

33"/"

577,

1955 - 37"/.t956 - 207.L957 - 7571958 - 22%

On the bottom there is a 15-20% mortality not occurring in trays. Ininterpretation of the tray mortalities one must remember that density ofplanting is important. That oysters pick up infections from tapers nearby isshorun by a \"/. death rate in one experimental group, compareC with a 2$"/., ratein comBarable trays but ivith infected oysters mlxed in.

Older kilIs:

l93O-l'tobjaclr Bay: Dur$fit report shor+s that this rr'ras a laEe rvinter-earlyspring ki11, with high mortalities on some grounds. Rumors indicatethat Ehis kill was more uidespread than just in Mobjack Bay.

llap-Rappat'ranScK F.iver ki l1-associated rvith heavy f resh waeer run-of f .Bottom blackeneC in May, oysters appeared OK in June but ruere deadby August .1"

1p!!-iiappahart:ctt* Ki11-assosicated r.,ith the hurricanes of that summert1958-Brorun shoal 1n James River had a L5-zO"L end-of-winter kiIl,

On the Eastern Shore--Andrervs had hearsay reports only:

Euring I95B there rt,ere severai complaints of unusual mortalities fromthe Seaside but few on the Bay si.de. Prior to this past season, repcrEs ofmortality have been lsolated and sporadic, Tt 1957 no complaints reached thegfl,. In 1956 one gro\.rer in Hol: Island Bay (ttto,t ?erry) reported heavy dioss ofoysters-verif ied by Sieling at 2540"L mortality, This r.,as market stock inB-10 feet of weter; a fall loss. Dredges on this ground-filled tvith seaurchins,

CAUSATIVE AGENTS

A. Defsrocystid,i_um. *'rndre\,rs, l.fyrhe, McDermott,

Andrewrs discussion of Chesapeake Bay mortalities above r..;as largely con-cerned with llermocystidium ancl included the patterBs of D. maritium ki 11. IIc-Dermott surrnarized D, marinum data. for Delarvare Bay. Since 1955 tde lrler., JerseyOyster Research LaU6?Iffis been studying the incidence and distributionof this fun.,?us on Nera.Iersey oyster grounds. The distribution elosely approxi-mates ttre disE.ribution of peak mortalities in the 1957-spring ki11 but the peakincidence, as shor.:n by the thioglyeollate method of Ray, is in September andearly OctobeE. DifferenE intensities of infection from L955-l) ttere eorrelatedruith summer temperat.ures-with the highest peaks occurring after the hottest

B,

-?-

summers. Based on experience with D. marinum in other areas Dr. J. L, MackinhasestimatedEhatatourIeve1ofTiffiinEhefa1tof195$hewou1dnotexpect over a 5% monthly mortality (for a 2-month perlod) actributable to thisfungus. It rvas poinEed out that the distribution ofi D. marinum in DelawareBay corresponds closely to the pattern of planting of-T;F;;ffioysters in thisdecade.

Various Parasites. Stauber

In seeking explanations for the unexplained mortalities, t.he most obviousone is ttrat a new etiological aEent j.s involved. It. is also obvious that' atleast theoretically, this might be vira1, spirochetal, bacterial, fungal,rickettslal or profozoan in nat.ure. The position taken \,ras thaE in an unex-plained mortali'.y no possibility can be overlooked.

Several lines of in.restigation, underrvay to explore Ehese possibillties,were presenced. fol1or'rin3 the sprinq of l)Jl mortal ityl Erganisms liku lgglgg]fj,Dermocysticlium and the ancistroeomid--1il:eenl*aite $7er6 sought for boEh in'freshoysters and in tissue sections of them, and an attempt was made to eva.luatetheir possibS,e role in the mortalities. There ls no evidenee, that any of theseis importantly involsed in't.he presen! rnortalities,

Bac ter ia.

r,r.tternpts to isoiate and characteri ze bacteria f rom healthy and dying oystersby Adelson in the fa1l of 1953 ruere described. OnIy tr.ro types of bacteri.a con-sistent,ly appeared in culEure of material (gapers and healthy oysters) takenfrom hi3h mortality grounds in contrast Eo the large numbers of bacEeria re-ported by Logie aird earlier by Fraser. Bio-chemical studies raith t.hese bac-teria are in progress. In addition, the fate of pure cultures of variousorganisms injectecl into the oysterrs blocd stream r^ras described. 1,trhile mostsuch organisms, of those already tesled, are read.ily destroyed in the oystertit is notervorthy fhat one bacterial associate nas able tc maintain itself lnthe oyster for a considerable period of time, I^Ihile none of these organismscan be incrirninated in the present outbreak, or definiEely associated,..rithoyster disease, the possibiltity should noE yet be discarded, Because ofdeficiency of meEl-iods no attenpts have been made yet to find intracellularparasites like viruses and rlckettsiae.

Trne "New Or8ani.smlt.

Fina11y, the nerr multinucleate-sphere, organism I'X'r, \^7as described, dis-tin3uished from Dermocystidiug, and its asssociation r.ri.th the Neru- Jersey out-break ani its possible relation to other outbreaks discussed, As a part ofthis, a demonstration segsion r.ras conCucted with displays of rnany of the knor^;nassociates of oysters. Fresh and stained r.ret mounls from oyst.ers or Dermo-cultures and stai.ned sections and smears of fixed material rvere avai. lable forstudy. In addition, sonre speciaL aspects of oyster 5istology r.uere shor'rn forcomparative purposes,

Tray Stqdies .,?ap? Shore, Haskin

To determine whether or not the suf.viors of the L957-spring mortality

C.

D.

)1.

_ 10_

i.rere carrying infeetive agents, a tr8y experiment rvas set up on the tide flatsof the Cape Shore ln June 1958. Seed oysters from J up*Bay Natural Seed Bedsand Cape Shore native yearlings r.rere mixed in various cornbinations with lot:er-?'ay 1957-kl11 survirrors, Seed oyst.ers atoae rvere the controls" l,lortalitiesr":ere hil1h in all trays in the September-December epidemic that swepl- th,roughDelar';are Bay r'rith no apprecieble dif ference betr",een experimental and controltrays. However, there vrere clefinite differences in the susceptibility of thevarious oyster stocks.

a" Seeci oysters, mosE. ly set ln 1956- f?orrMiddle, Cohansey and ShelI Rocknatural be<1s shor-:ed the hiai:est mortalities with peak monthly ratesranging frorn 3O to 40% . '

b, Larger oysters from the plant.ed qrounds and from the lower NaEuralSeed Beds had monthly rhortalities ranging generally between 10 &nd20.1_

cr Yearling Cape Shore natives had tlre lor,'est mortalities r.rith monthlyrates ranging Eetr^reen 5 aad L5"/".

;\11 gapers from t.hese trays have been fixed and are being processed forhistolqilrical study, Virtual. ly all exan:ined to date shot^r the ?rX Or.3anismsrr -frequently in very hi.gh concentration. Nlortalities rvere at peak lEvels inSeptember and October - eorresponClng vrith peak kills on the planted grounds.There is some indieation of minimal mortality during the high Eemperature per-iod of late June, July and August but this is noL certain because of the laEesEarting date for the trays.

1958 spat on Ehe Cape Shore t.ide f lats, f ixed in late ltrovernber, are a1-ready hear..i1y infected with 'rX.tr This indicates that the yearling oystersfrom this area usecl in.the tray experi.ments ma)' have undergone an initial mor-tality and screening ouE of suseepttbles.

WORK T,l BE Di)l.lE

This portion of the conference t.res a general consideration of lines ofraork to be pursued. The Neu' Jersey group indicated plans for vork to be donea-nd askecl f or comments and sug.,gsgions,

Ig '.,,65 emphasized that the primary objective is to determine if EherrX organismrr is the patirogen responsible for the :pidemi.c Cisease in DelawareB.y. So far all observations on distri.bution anC intensiEy of infection areeonsistent with t,he hypothesis that it is indeed responsibl.e. It is intendedto continue the monthly field samplin3 on selected oyster gror-rncls and theNatural Seed Beds. These sanrpl in?s '..ri 11 provide f ixed material to i5g inv:ith observed mortaliti.es. ContinueC histological study, roith Ehe cooperationof Dr. J, G. Iiackin and perhaps Dr. Jchn Karling, r^ri1l probably lead to theidentification of trxtt and more knor.,'ledge of its tife cycle, anC histopathology.

Iir. Scheltema at the Cape Shore Laboratory has set-up aquarium experimentstaith uninfected stoc!<s mixed in raith oysters from high-mortality grounds, todeternine i,f infecti.ons can be transferred readily from oyster to oyster. Itis anLicipated that Dr. l"iackint s Eechniques r.rith Derrnocyst.idium inf ectionsrvill be ernployed here r"rhen sea-r",ater facilities are available. The developmentof reliable infection techniques roith'rXorganismrt may permit short-ternn studieson host resistance.

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rt is antieipated that the inoculation r':ork of the Ner+ Brunsrvick grouproi11 also be continued. .rlthough prtmary emphasis is on the *x orga,.risms,',the leads with 2 cifferent bagteria .r" "tror,g enough to justify some in-oculation studies viith Ehese,

The members of the conference cornrnented favorabry on the Droposed. linesof attack in New -Tersey' Marylanc and virginia representatives inriicated thatthey r.:cu 1d:

a' l'Jatch carefully for further evidences of oyster nicrtalities in theirareas anC,b' Commence at once a survey of areas and fixat.ion of oysters to searchfor thettnew organismrt and to provice baei<ground data for future mor-tality studies.

rt ruas generally agreed that any effective conErol measures for thecausative agent in the lleiaware Bay mortalities would require knor+ledge ofits life cvele and possi.ble l-imiEing facrors, The chief 'h;p; ior the in_dustry is that streins of oysters resistant to this agent may be selected inDelar'rare Bay' To faeilitate Ehe selecti.on of such strains il rvas agreed thattransfers of oysters into and out of the Bay shourd be held at a minimum.