The document outlines various diseases affecting oysters, mussels, and other mollusks, detailing their causative agents, symptoms, diagnostic techniques, and prevention strategies. Notable diseases include MSX disease, Dermo disease, Marteiliosis, Bonamiasis, Mytilicolosis, and bacterial infections such as Brown Ring Disease and Larval Vibriosis. Most diseases have no known prevention or control methods, emphasizing the importance of monitoring and managing environmental conditions.

1. Notable Disease of Oysters,
Mussels and Other Mollusks
TG Bonjuana de la Peña Cañal

2. Diseases Caused by Parasites

3. MSX Disease (Multi-nucleated Sphere X)
or Haplosporidiosis
Causative Agent:
• The protozoan, Haplosporidium nelsoni
Symptoms/Signs:
• Lesions in the digestive glands and gills in clams
• Decreased condition (meat quality) of oysters
• Reduced reproductive capacity in oysters
• High mortality rate

4. Diagnostic Techniques:
• Microscopic examination (Histological diagnostic techniques)
Prevention and control:
• No known methods of prevention and control
• Salinity control (≥ 20 ppt)
• Selective breeding

5. Dermo Disease (Perkinsiosis)
Causative Agent:
• Perkinsus atlanticus, P. olseni and P. marinus
Signs/Symptoms:
• Visible milky white cysts or nodules on the gills, foot and mantle
• Lesions
• Large-scale mortalities (clams and abalones)

8. Diagnostic Techniques:
• Histology, fluid thioglycollate medium (FTM) assay and PCR
Prevention and Control:
• No reports of methods of control in the natural environment
• Mortality can be minimized by avoiding stressful conditions.
• High densities
• High temperature (esp. during harvesting)

9. Marteiliosis
Causative Agents:
• Marteilia refringens, M. maurini and M. sydneyi
Symptoms/Signs:
• Recurring mortality of flat oysters
• Poor condition index with glycogen loss (ernaciation)
• Discoloration of the digestive gland
• Cessation of growth
• Tissue necrosis and mortality

10. Diagnostic Techniques:
• Digestive gland imprints, histology, TEM, in situ hybridization and PCR
Prevention and Control:
• No available control methods
• Knowledge of the life cycle of Marteilia could provide management
strategies

11. Bonamiasis
Causative Agents:
• Bonamia ostreae and B. exitiosus
Symptoms/Signs:
• Shell gaping
• Lesions in the connective tissues of the gills, mantle and digestive
gland
• Some have yellow discoloration and/or lesions on the gills or mantle

12. Diagnostic Techniques:
• Tissue (gill, heart) imprints, histology or TEM
Prevention and Control:
• No reports but mortality can be lessened by reducing oyster density

13. Mytilicolosis
Causative Agents:
• Mytilicola spp.
Symptoms/Signs:
• Poor growth and condition
• Extensive damage of the gut wall and sporadic mortality

14. Diagnostic Techniques:
• Gross observations, histology and enzyme extraction
Prevention and Control:
• No known methods of prevention or control except of good
husbandry

15. Disease Caused by Virus

16. Herpes-like virus of oysters
Causative Agents:
• Not Established
Symptoms/Signs:
• Herpes like infection (oyster larvae and spat)
• Associated with mass mortality (80-90%)
Diagnostic Techniques:
• Histology, TEM, PCR and in situ hybridization
Prevention and Control:
• No method of prevention and control are known

17. Diseases caused by Bacteria

18. Brown Ring Disease (BRD)
Causative Agents:
• Vibrio tapetis
Symptons/Signs:
• Disease was only reported from Tapes philippinarum and T.
decussatus (clams)
• Secretion causing brown deposit of organic material
• Shell deposition
• Decrease in glycogen

19. Diagnostic Techniques:
• Observation of gross signs
• Electron microscopy
• Immunoassays
• Culture and bacteriological identification
Prevention and Control:
• Reduction of Clam density

20. Larval vibriosis
Causative Agents:
• Vibrio tubiashi, V. anguillarum, V. splendidus, Vibrio ordali, V.
alginolyticus and Vibrio spp.
• Pseudomonas and Aeromonas
Symptoms/Signs:
• Necrosis of mantle epithelium
• Sudden onset with the affected larvae exhibiting reduced feeding rate
• Erratic swimming behaviour

21. Diagnostic Techniques:
• Biochemical, immunodiagnostic, or molecular methods
• Histology
Prevention and Control:
• Under investigation

22. References
• Alvarez-Pellitero P. (ed.), Barja J.L. (ed.),Basurco B.(ed.), Berthe F.
(ed.), Toranzo A.E. (ed.). 2004. Mediterranean aquaculture diagnostic
laboratories. Zaragoza, CIHEAM. p. 33-48 (Options Méditerranéennes
: Série B. Etudes et Recherches; n. 49