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www.elsevier.nlrlocateraqua-online

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/

Prevalence of Perkinsus marinus Dermo in

Crassostrea

Õ

irginica along the Connecticut

shoreline

John Karolus

)

_{, Inke Sunila, Stacey Spear, John Volk}

Connecticut Department of Agriculture, Bureau of Aquaculture, 190 Rogers AÕenue, P.O. Box 97, Milford,

CT 06460, USA

Received 9 May 1999; received in revised form 25 August 1999; accepted 8 September 1999

Abstract

The prevalence of Perkinsus marinus in the eastern oyster CrassostreaÕirginica along the

Connecticut shoreline was surveyed during a period of 2 years from 1996 to 1997. The survey was conducted in shallow and deep waters. Fifty-four samples involving 1430 oysters were tested. Using Ray’s Fluid Thioglycollate Medium, the parasite was found at all sampling locations with a prevalence range from 10% to 100%. The weighted prevalence values were significantly greater in

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shallow waters compared to deep waters in 1996 t-test, P-0.05 . However, in 1997, the

difference between the two areas was not significant. The results demonstrated P. marinus had established enzootics throughout the Connecticut shoreline. Oyster aquaculture practices of transplanting natural seed from shallow waters to approved areas found in deeper waters had

probably resulted in comparable weighted prevalence values between these areas.q_{2000 Elsevier}

Keywords: Perkinsus marinus; Dermo; Connecticut

1. Introduction

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Perkinsus marinus Dermo was identified in the late 1940s as the cause of extensive

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oyster mortalities in the Gulf of Mexico. Along with Haplosporidium nelsoni MSX ,

)_{Corresponding author. Tel.:}_q_{1-203-874-0696; fax:}_q_{1-203-783-9976; e-mail: dept.agric@snet.net}

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( ) J. Karolus et al.rAquaculture 183 2000 215–221

216

both parasites have caused hundreds of millions of dollars in losses in the Chesapeake

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and Delaware Bays Ewart and Ford, 1993 .

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Sindermann 1969 reported the pathogen’s presence in Long Island Sound oysters in

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1968. However, Ford 1996 reported that a number of surveys, as well as occasional sampling by several laboratories, had never found conclusive evidence of the pathogen north of New Jersey before 1991. Ford concluded the parasite’s presence must have been scattered and sparse to have been missed by the survey work she reported in 1996. In early May 1992, very light infections were detected in 65–70% of oysters from Oyster Bay, located on the north shore of Long Island, NY and from the Connecticut shore of Long Island Sound. Known infection patterns indicate the pathogen must have been present in a substantial number of oysters the year before to have caused such a

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prevalence in 1992 Ford, 1996 . Brousseau 1996 reported the presence of Dermo in Westport, Bridgeport and Milford, CT during the time from September 1993 to December 1994. The majority of the infections at all sites were classified as light. In 1996, she found an increase in prevalence and weighted prevalence at two of these sites.

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According to Ford 1996 , Dermo had a prevalence of 75%–100% and weighted prevalence of 2.5 or more in many Long Island Sound locations by late summer of 1995. Based on the literature results and with the occurrence of a depletion of natural oyster seed from some economically important oyster beds in 1996, we decided to examine the oyster population for the presence of Dermo to determine if there was a continued increase in the prevalence or intensity of infection along the Connecticut shoreline.

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Oysters sampling sites were categorized as follows: 1 shallow waters where the oyster

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population was primarily seed; 2 deeper water locations classified as approved according to the National Shellfish Sanitation Program and Interstate Shellfish

Sanita-Ž .

tion Conference 1997 .

2. Materials, methods and techniques

A map of the sampling sites is shown in Fig. 1. In 1996, 20 oysters were sampled from each station. In 1997, 30 oysters were used from each location. The shallow water sites were intertidal, as well as subtidal with the water being 2.5 m or less deep. The deep water locations were areas approved for market harvest, with depths from 2.5–12 m. Testing was done with 2–4 year oysters. Ray’s Fluid Thiogylocollate Medium containing 2% NaCl and supplemented with a final concentration of 50 units of

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penicillin G and 50 mg of streptomycin sulfate per ml of medium was used Bushek et

. 3

al., 1994 . Approximately 0.5 cm of labial palps, mantle, digestive glands and rectalranal tissue were removed. The tissues were incubated in the medium for 5–12 days at room temperature. The intensity of the infection in the oyster was rated using the

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218 Table 1

Prevalence and weighted prevalence of P. marinus from shallow waters in 1996

Town Date Location Weighted Prevalence

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prevalence %

X X

Greenwich 05r09r96 41801.21 N:73835.74 W 0.8 80

X X

Greenwich 05r09r96 41801.05 N:73834.52 W 0.6 80

X X

Branford 05r28r96 41815.73 N:72845.63 W 1.2 100

X X

Greenwich 07r11r96 41801.05 N:73834.52 W 1.6 100

X X

Greenwich 07r11r96 41801.21 N:73835.74 W 2.5 100

X X

Greenwich 08r22r96 41801.05 N:73834.52 W 2.5 100

X X

Greenwich 08r22r96 41801.21 N:73835.74 W 2.8 100

X X

Bridgeport 09r12r96 41808.50 N:73809.40 W 1.1 80

X X

Bridgeport 09r12r96 41808.50 N:73809.40 W 2.2 100

X X

Greenwich 09r19r96 41801.05 N:73834.52 W 2.6 100

X X

Greenwich 09r19r96 41801.21 N:73835.74 W 3.0 100

X X

Greenwich 11r19r96 41801.05 N:73834.52 W 2.1 100

X X

Greenwich 11r19r96 41801.21 N:73835.74 W 2.2 100

X X

Milford 11r20r96 41812.73 N:73803.14 W 1.3 100

X X

Waterford 11r24r96 41819.00 N:72810.63 W 0.01 10

X X

Stonington 12r02r96 41821.02 N:71853.01 W 1.4 60

X X

New Haven 12r18r96 41818.00 N:72854.00 W 1.3 100

For statistical analysis, the t-test used was the significance test on a difference

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between two independent sample means, population variance not known Bahn, 1972 .

3. Results

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The prevalence percentage of infected oysters in a sample and weighted prevalence results for P. marinus are shown in Tables 1–4. P. marinus was found at all sampling

Table 2

Prevalence and weighted prevalence of P. marinus from deep waters in 1996

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prevalence %

X X

Guilford 05r14r96 41816.00 N:72840.47 W 0.07 40

X X

Milford 05r24r96 41810.85 N:73802.35 W 0.05 40

X X

Westport 06r02r96 41804.50 N:73822.60 W 0.5 100

X X

Madison 06r16r96 41816.10 N:73836.00 W 0.9 60

X X

Norwalk 07r08r96 41805.16 N:73823.07 W 0.5 80

X X

Norwalk 07r08r96 41803.88 N:73824.13 W 0.8 60

X X

Westport 07r08r96 41803.01 N:73822.21 W 0.2 40

X X

Madison 08r22r96 41816.02 N:72836.00 W 2.9 100

X X

Guilford 09r29r96 41816.00 N:72809.47 W 2.3 100

X X

Guilford 10r14r96 41816.05 N:72839.62 W 2.4 100

X X

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Table 3

Prevalence and weighted prevalence of P. marinus from shallow waters in 1997

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prevalence %

X X

Greenwich 01r15r97 41801.21 N:73835.74 W 0.8 100

X X

Greenwich 01r15r97 41801.05 N:73834.52 W 1.2 90

X X

Waterford 03r04r97 41819.03 N:72810.63 W 0.2 30

X X

Madison 04r04r97 41816.00 N:72836.00 W 0.8 50

X X

Clinton 04r06r97 41815.97 N:72832.00 W 0.8 90

X X

Guilford 04r06r97 41816.05 N:72839.62 W 0.3 70

X X

Bridgeport 06r25r97 41809.08 N:73810.28 W 0.6 40

X X

Greenwich 07r15r97 41801.21 N:73835.74 W 1.9 90

X X

Bridgeport 08r29r97 41808.50 N:73809.40 W 2.2 100

X X

Greenwich 09r15r97 41801.05 N:73834.52 W 0.7 80

X X

Guilford 09r28r97 41816.05 N:72839.62 W 2.8 100

X X

Clinton 10r14r97 41815.97 N:72832.00 W 2.1 100

X X

Stratford 11r12r97 41809.94 N:73806.04 W 1.1 100

X X

Bridgeport 11r12r97 41809.08 N:73810.28 W 0.6 60

X X

Clinton 12r07r97 41816.05 N:72831.30 W 1.1 90

X X

Clinton 12r07r97 41815.97 N:72832.84 W 1.4 100

X X

Fairfield 12r06r97 41809.21 N:73814.00 W 0.1 10

Norwalk 12r17r97 41802.42X

N:73825.25X

W 2.0 90

locations which spanned the entire Connecticut shoreline. In addition to location, Fig. 1 reveals the mean weighted prevalence results with the year of testing. The values for each year may represent both shallow and deep water sampling. Using the significance test, in 1996, the shallow water samples had significantly higher weighted prevalence

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values than the deep water samples ts5.4, P-0.05s1.706 . However, the

differ-Ž .

ence between the two areas was not significant in 1997 ts0.3, P)0.05s1.711 . During our study in 1996, many oyster meats appeared healthy by gross examination even though they were infected with P. marinus at a Mackin value of 3.0 or greater.

Table 4

Prevalence and weighted prevalence of P. marinus from deep waters in 1997

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prevalence %

X X

Madison 05r28r97 41816.00 N:72836.00 W 0.5 90

X X

Westport 07r03r97 41803.00 N:73823.46 W 0.2 20

X X

Westport 08r27r97 41804.49 N:73822.61 W 2.0 100

X X

Westport 09r24r97 41804.49 N:73819.79 W 0.9 90

X X

Norwalk 12r17r97 41802.42 N:73825.25 W 0.3 40

X X

Westport 12r17r97 41802.73 N:73822.21 W 1.3 90

X X

Norwalk 12r17r97 41803.36 N:73825.12 W 1.7 90

X X

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220

4. Discussion

Our results indicated P. marinus was firmly entrenched in the CrassostreaÕirginica population along the Connecticut shoreline. As stated earlier, the shallow areas in 1996 had significantly higher weighted prevalence values than the deep water areas. The shallow water samples contained a number of natural or wild oyster seed areas. One would expect the shallow waters to have a higher temperature than the deep waters. The higher temperatures in addition to the salinity values for all sampling locations being above 15 ppt were conducive for Perkinsus proliferation. These shallow areas supply seed for planting in the deep water-growing areas. Hence, the continual restocking of infected oysters into approved market harvest areas could have resulted in the difference between weighted prevalence values for the two areas being not significant in 1997.

Even with high weighted prevalence values, there had been no reported wide spread oyster mortalities in 1996. Some of the samples in the present article had approached

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weighted prevalence values 3.0 of the parasite, levels that were responsible for severe

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oyster mortalities in the Gulf of Mexico Mackin and Hopkins, 1961 . Severe epizootics

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of H. nelsoni occurred throughout Long Island Sound in 1997 Sunila et al., 1999 . With the epizootics of H. nelsoni, it was impossible to assess the effect of P. marinus alone on the C.Õirginica population in Long Island Sound. The MSX parasite may have been present in low numbers in 1996. Unfortunately, testing for this parasite was not done in 1996. Infection of C. Õirginica with H. nelsoni resulted in oysters physio-logically stressed to the point of death. We believe this occurred at the towns listed in Fig. 1 where there was a decrease in the weighted prevalence from 1996 to 1997. The towns that had an increase in the weighted prevalence were sampling sites in deep waters where the prevalence of H. nelsoni had not caused significant oyster mortalities at the time of sampling. Therefore, surviving oysters had additional time to increase

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their Perkinsus parasite load. According to Brousseau et al. 1998 , wild oysters collected along the central Connecticut shoreline were largely uninfected. This was not in accordance with the results of this study. In fact, some of the highest weighted

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prevalence values were found from wild oysters in this region of the state Tables 2 and

.

3 . The state-wide presence of P. marinus and the epizootic presence of H. nelsoni

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make management strategies extremely difficult as Brousseau et al. 1998 suggested.

5. Conclusion

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References

Bahn, A.K., 1972. Basic Medical Statistics. Grune and Stratton, New York, 260 pp.

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Brousseau, D., 1996. Epizootiology of the parasite, Perkinsus marinus Dermo in intertidal oyster populations from Long Island Sound. J. Shellfish Res. 15, 583–587.

Brousseau, D., Guedes, J.C., Lakatos, C.A., Lecleir, G.R., Pinsonneault, R., 1998. A comprehensive survey of Long Island Sound oysters for the presence of the parasite, Perkinsus marinus. J. Shellfish Res. 17, 255–258.

Bushek, D., Ford, S.E., Allen, S.K. Jr., 1994. Evaluation of methods using Ray’s fluid thiogylocollate medium for the diagnosis of Perkinsus marinus infection in the eastern oyster, CrassostreaÕirginica. Annu. Rev.

Fish Dis. 4, 201–217.

Ewart, J., Ford, S.E., 1993. History and impact of MSX and Dermo diseases on oyster stocks in the Northeast region. Northeast Regional Aquaculture Center fact sheet no. 200.

Ford, S., 1996. Range extension by the oyster parasite Perkinsus marinus into the northeastern United States: response to climate change? J. Shellfish Res. 15, 45–56.

Mackin, J.G., Hopkins, S.H., 1961. Studies on oyster mortality in relation to natural environments and oil fields in Louisiana. Publ. Inst. Mar. Sci., Univ. Tex. 7, 1–131.

National Shellfish Sanitation Program, Interstate Shellfish Sanitation Conference, 1997. Guide for the Control of Molluscan Shellfish. U.S. Department of Health and Human Services, Public Health Service. Food and Drug Administration, 406 pp.

Ray, S., 1954. Biological studies of Dermocystidium marinum a fungus parasite of oysters. The Rice Institute Pamphlet, Special issue, 114 pp.

Sindermann, C., 1969. Oyster mortalities, with particular reference to Chesapeake Bay and the Atlantic Coast of North America. U.S. Dept. of Interior US Fish and Wildlife Service Special Scientific Report — Fisheries No. 569.

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