Trematode Metacercariae of Abalone

Category

Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Metacercarial infection of abalone.

Scientific name or taxonomic affiliation

Various species of Digenea including species in the family Allocreadiidae and possibly Opeocoilidae. Because only incompletely developed juvenile stages of the parasite occur in abalone, the specific identities of the trematodes involved are not known.

Geographic distribution

Only reported from Australia and southern Africa but probably have a global distribution. However, each species may be confined to certain areas.

Host species

Reported from Haliotis ruber, Haliotis roci, Haliotis tuberculata and Haliotis spadicea as well as various other molluscs including oysters, mussels and clams and cockles and from sea urchins.

Impact on the host

In most cases, the prevalence and intensity of infection appears to be low. Encystment of the parasite in the foot musculature, digestive gland, gill filaments or gonad does not appear to affect the survival of the abalone host but may cause castration. However, at the De Hoop Nature Reserve in southern Africa, the prevalence of infection was high (greater than 50%) and in some abalone, hundreds of digeneans encysted inside the gills caused them to be orange in colour (Botes et al. 1999).

Diagnostic techniques

Squash Preparations: Thin slices (about 3 mm thick) of the abalone body pressed between two plexiglass plates and examined under a dissecting microscope (50 ×) show metacercariae.

Histology: Cross sections of metacercariae can be observed within the tissues.

Methods of control

Prevention and control impractical. The trematodes involved require development to the adult stage in a vertebrate host to complete the life cycle before the parasite can be transmitted to other abalone. With many trematodes, only specific species of vertebrates can serve as suitable final hosts. This requirement limits the potential of trematodes to cause a problem in another habitat or within an abalone culture facility.

References

Botes, H., L. Basson and L.L. Van As. 1999. Digenean trematodes found associated with Haliotis spadicea Donovan, 1808. Proceeding of the Microscopy Society of Southern Africa 29:76.

Harrison, A.J. and J.F. Grant. 1971. Progress in abalone research. Tasmanian Fisheries Research 5:1-10.

Shepherd, S.A. and P.A. Breen. 1992. Mortality in abalone: its estimation, variability and causes. In: Shepherd, S.A., M.J. Tegner and S.A. Guzman del Proo (eds), Abalone of the World. Biology, Fisheries and Culture. Proceedings of the 1st International Symposium on Abalone. Fishing News Books, Blackwell Scientific Publications, Ltd., Oxford, pp. 276-304.

Citation Information

Bower, S.M. (2002): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Trematode Metacercariae of Abalone.

Date last revised: February 2002
Comments to Susan Bower

Date modified: