Bonamiosis in Ireland: Current Perspectives

Transcription

1 Bonamiosis in Ireland: Current Perspectives Sarah C. Culloty, Zoology, Ecology & Plant Science, Aquaculture & Fisheries Development Centre/ERI, University College Cork ERI Environmental Research Institute

2 Oyster Fishing in Ireland: History Lough Foyle Natural Fisheries around the south, west and north coasts Managed beds Cork Harbour Cork Harbour

3 Oyster Production currently O. edulis and C. gigas production in Ireland in N o. Oper ator s P r oduction (T) O. edulis C. gigas

4 Bonamia ostreae Haplosporidian 2-3 µm Hemocytes Multiplies: binary fission Uni-, multi- cellular forms, plasmodial form

5 Spread of B. ostreae Introduced to France late 1970s (spat from California) Spread with consignments to Spain and the Netherlands England 1982 Ireland diagnosed 1987 Found on both coasts of U.S.

6 Introduction to Ireland Initial introduction Cork Harbour 1987; Latest Lough Foyle summer 2005

7 Screening of frozen oysters Level Of Infection None Light Heavy 3 year old oysters (%) year old oysters (%)

8 ho riz ra ut ut w ith Histology Heart/Hemolymph smears ta ho Light Microscopy: ou at io n Diagnostics is td no PCR In situ hybridisation o se m in at e Molecular techniques D

9 Techniques to reduce mortalities Presently cannot be eradicated Reduce stocking density Reduce handling Depth of culture? Reduce Stress Development of resistant stock

10 Mechanisms for preventing the spread of B. ostreae No movements of oysters for relaying from areas where the parasite is present Ensure that no oysters are brought in with other movements of bivalves Care with use of equipment in infected and uninfected areas

11 Cork harbour Enclosed area, Shallow, Little tidal exchange Managed beds

12 Infected oyster Transmission of B. ostreae /Life cycle B. ostreae in water Other Host/Carrier? Uninfected oyster Transmission directly from oyster to oyster May be other stages in the life cycle?

13 F eb-90 Apr J un Aug Oct Dec F eb Apr J un Aug Oct Dec Seasonal/Age related variation Pr ev of Inf. (%) i n 18 m t h oyst er s over 24 m ths P r evalence of Infection (%) Month P rev of Inf. (%)

14 Other molluscs? Transmission trials carried out on: Mussels, Pacific oysters Manila clam Native clam

15 Questions Sensitivity of diagnostic techniques? Are all sized/aged oysters susceptible? Life Cycle: Spore stage? What is happening during the latent period? Is there a secondary host/carrier species involved in the life cycle? Can a resistant stock be produced? Host/Parasite interaction?

16 Diagnostic/Screening techniques Histology vs Heart/Hemolymph Screening e.g; latent period Molecular techniques: PCR optomised? Higher prevalence than heart smears Some positives with heart smears not PCR and vice versa

17 Susceptibility of young oysters to B. ostreae 2 field sites: Cork and Galway 2 age groups: 0+ and 1+ Monitored in the field over six months

18 Results of study (Cork Harbour) Population SS0 + R0+ T1+ N Initial Sample Hs (%) PC R % N months Hs (%) PC R % N months Hs (%) PC R % N months Hs (%) PC R % R

19 Intermediate/reservoir host Objectives: Screen inverts (benthic and zooplankton) for presence of B. ostreae Lab trials to confirm role of any inverts found to be positive for B. ostreae

20 Cork Harbour Survey Class Species Quantity (n) Anthozoa Actina equina 29 Gymnolaemata Alcyndium dicphanum 5 Gymnolaemata Alcyndium gelatinosum 3 Gymnolaemata Alcyndium mytili 5 Crustacea Ampelisca 51 Ascidiacea Ascidiella aspersa 3 Demospongiae Axinella dissimilis 6 Gastropoda Calyptrae chinensis 3 Crustacea Carcinus maenas 8 Crustacea Corophium 10 Holothuroidea Holothuroidea 2 Polychaetea Hormothoe impar 3 Bivalvia Mytilus edulis 8 Polychaetea Nephthys 144 Ophiuroidea Ophiothrix fragilis 54 Polychaetea Polychaete sp 4 Polychaetea Sabella pavonina 87 Polychaetea Scoloplos armiger 16 Bivalvia Scrobicularia plana 25 Oligochaeta Tubificoides benedii taxa and 1144 individuals screened to date

21 Comparison of fauna from different study sites Species Quantity(n) PCR replicates Result Actinia equina Total positives Nephthys Total positives Ophiothrix fragilis Total positives Sabella pavonina Total positives

22 Screening of Zooplankton Station 1 Station2 Station 3 Station 4 Station 5 January (2004) February March April May June July August September October November December January (2005) February March April

23 Control/Eradication/Resistance Cannot be eradicated from an area Treatment not possible Development of resistance Studies on Irish oysters Studies on European populations

24 Irish Populations Cork harbour (Rossmore): lowest prevalence of infection lowest mortality Naïve populations more susceptible L. Foyle Rossmore Tralee Dec-96 Jan-97 Feb-97 Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec-97 Jan-98 Feb-98 Mar-98 Apr-98 May-98 Jun-98 Month Rossmore Tralee Prevalence of Infection (%)

25 European Study

26 European populations ROSSMORE class 0 class 1 class 2 class 3 class 4 100% 80% 60% 40% 20% 0% 100% 80% 60% 40% 20% 0% Lough Kishorn class 0 class 1 class 2 class 3 class 4 Jun-98 Sept Dec Mar-99 June Oct Jan-00 Jun-98 Sept Dec Mar-99 June % of oysters Oct Jan-00 Month

27 Current Concerns Further spread of B. ostreae; Management of beds where B. ostreae is present; Overfishing; Conservation of a native species Abandon O. edulis for C. gigas Experiences of different management plans.