Proctoeces maculatus Trematode Disease of Mussels


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Mussel trematode disease.

Scientific name or taxonomic affiliation

Proctoeces maculatus reported under a wide variety of synonyms including: Cercaria tenuans, Cercaria milfordensis, Cercaria brachidontis, Proctoeces subtenuis, Proctoeces scrobiculariae, and Proctoeces buccini (family Fellostomidae).

Geographic distribution

Widely distributed in tropical and temperate marine waters including the east coast of the United States (for summary of locations see Sunila et al. 2004), but not yet reported from Canada.

Host species

Sporocysts only reported from Mytilus edulis, Mytilus galloprovincialis and Ischadium recurvum. However, all other life stages have a wide host tolerance. Metacercariae occur in various Mollusca including oysters, Polychaeta and Echinoidea. Adults occur in tropical mollusc-eating fish (labrids and sparids) and temperate Gastropoda, Lamellibranchiata and Polychaeta. Adults have also been observed in the same invertebrate hosts as the sporocysts.

Impact on the host

Infection causes an alteration in haemolymph components, a reduction in growth rate, and weakness with respect to valve closure and attachment to the substrate. In heavy infections, the numerous sporocysts developing in the mantle can seriously reduce glycogen content (energy reserves) of the tissues and efficiency of the circulatory system, resulting in disturbances to gametogenesis and possibly castration and death. In one location (Ria de Aveiro, Portugal), prevalence was reported to be higher in male mussels and there was evidence of parasite rejection in some mussels. Often occurs in low prevalences (less than 1%) and thus may not be a threat to mussel culture in some enzootic areas (Robledo et al. 1994b, Villalba et al. 1997). However, prevalence in mussels at one location can vary over time. For example, Canzonier (1972) reported a low prevalence (4%) that was interpreted as responsible for minimal losses in natural and cultured mussel (M. edulis) populations in Laguna Veneta, Italy. About 10 years later, this parasite was identified as the probable cause of an extensive mortality in cultured mussels (M. edulis/galloprovincialis) from the same location (Munford et al. 1981). Also, Sunila et al. (2004) determined that heavy infections (over 60%) that occurred in M. edulis from an experimental long-line culture system in Long Island Sound, Connecticut, USA would limit the aquaculture of mussels in that location to a seasonal product (within the first 6 months after seed set and prior to September).

Diagnostic techniques

Gross Observations: Sporocysts, often containing developing cercariae, in mantle, visceral mass, or gonad. Sporocysts of P. maculatus are usually deep orange-pigmented and most evident in the mantle of mussels in poor condition. This species can be differentiated by the morphology of the cercariae (Bray 1983).

Histology: Various life stages in the vascular system of mussel sections of the digestive gland, foot, kidney, gonad and gills. This parasite may elicit a heavy haemocytic response including granulocytomas in which the trematode is encapsulated and frequently destroyed.

Methods of control

No known methods of prevention or control. Because P. maculatus can complete its life cycle in mussels, mussels from areas known to be infected (currently or historically) should not be transferred to areas with no record of P. maculatus. However, the hazard may be minimal due to the limited range of ecological conditions under which P. maculatus disseminates.


Bower, S.M. 1992. Diseases and parasites of mussels. In: Gosling, E. (ed), The Mussel Mytilus: Ecology, Physiology, Genetics and Culture. Elsevier, Amsterdam, pp. 543-563.

Bower, S.M. and A.J. Figueras. 1989. Infectious diseases of mussels, especially pertaining to mussel transplantation. World Aquaculture 20: 89-93.

Bray, R.A. 1983. On the fellodistomid genus Proctoeces Odhner, 1911 Digenea) with brief comments on two other fellodistomid genera. Journal of Natural History 17: 321­339.

Canzonier, W. 1972. Cercaria tenuans, larval trematode parasite of Mytilus and its significance in mussel culture. Aquaculture 1: 267-278.

Feng, S.L. 1988. Host response to Proctoeces maculatus infection in the blue mussel, Mytilus edulis L. Journal of Shellfish Research 7: 118.

Lauckner, G. 1983. Diseases of Mollusca: Bivalvia. In: O. Kinne (ed.) Diseases of Marine Animals. Volume II: Introduction, Bivalvia to Scaphopoda. Biologische Anstalt Helgoland, Hamburg, p. 632-673.

Machkevski, V.K. 1985. Some aspects of the biology of the trematode, Proctoeces maculatus, in connection with the development of mussel farms on the Black Sea. In: J.W.J. Hargis (ed.) Parasitology and Pathology of Marine Organisms of the World Ocean. U.S. Department of Commerce, p. 109-110.

Munford, J.G., L. DaRos and R. Strada. 1981. A study on the mass mortality of mussels in the Laguna Veneta. Journal of the World Mariculture Society 12: 186-199.

Robledo, J.A.F., J. Caceres-Martinez and A. Figueras. 1994a. Mytilicola intestinalis and Proctoeces maculatus in mussel (Mytilus galloprovincialis Lmk.) beds in Spain. Bulletin of the European Association of Fish Pathologists 14: 89-91.

Robledo, J.A.F., M.M. Santarém and A. Figueras. 1994b. Parasite loads of rafted blue mussels (Mytilus galloprovincialis) in Spain with special reference to the copepod, Mytilicola intestinalis. Aquaculture 127: 287-302.

Sunila, I., L. Williams, S. Russo and T. Getchis. 2004. Production and pathology of blue mussels, Mytilus edulis (L.) in an experimental longline in Long Island Sound, Connecticut. Journal of Shellfish Research 23: 731-740.

Teia dos Santos, A.M. and J. Coimbra. 1995. Growth and production of raft-cultured Mytilus edulis L., in Ria de Aveiro: gonad symbiotic infestations. Aquaculture 132: 195-211.

Villalba, A., S.G. Mourelle, M.J. Carballal and C. López. 1997. Symbionts and diseases of farmed mussels Mytilus galloprovincialis throughout the culture process in the Rías of Galicia (NW Spain). Diseases of Aquatic Organisms 31: 127-139.

Wardle, W.J. 1980. On the life cycle stages of Proctoeces maculatus (Digenea: Fellodistomidae) in mussels and fishes from Galveston Bay, Texas. Bulletin of Marine Science 30: 737­743.

Citation Information

Bower, S.M. (2009): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Proctoeces maculatus Trematode Disease of Mussels.

Date last revised: June 2009
Comments to Susan Bower

Date modified: