Mytilicola orientalis infestation (oyster redworm)
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Mytilicola orientalis infestation
Preferred Common Name
- oyster redworm
International Common Names
- English: oyster red worm
OverviewTop of page
Mytilicola orientalis was first described by Mori (1935) from the gut of bivalves in Japan. It was subsequently erroneously redescribed as Mytilicola ostreae by C. B. Wilson in 1938 from oysters imported into Puget Sound, Washington, USA, from Japan. Thus, M. ostreae is a synonym of M. orientalis (Odlaug, 1946; Cheng, 1967; Lauckner, 1983). Mori (1935) initially assigned this copepod to the family Dichelestiidae in accordance with Steuer (1902). Cheng (1967) supported placement in the family Clausiidae but M. orientalis is now included in the family Mytilicolidae (Lauckner, 1983). The red colour of M. orientalis makes it easy to see within the intestinal tract of dissected bivalves. Because of the relatively elongate morphology and small limbs of this parasitic copepod, it looks like a worm to the unaided eye, hence the common name of red worm. Although the pathological significance of M. orientalis for its bivalve hosts is controversial, there is no associated human health risk. However, from the perspective of consumers, the aesthetic value of infected oysters might be impaired (Sparks, 1962).
Hosts/Species AffectedTop of page
Mytilicola orientalis infests the intestinal tract of a wide range of mollusc hosts (mostly bivalves) including Crassostrea gigas, Ostrea lurida [Ostrea conchaphila], Ostrea edulis, Mytilus crassitesta [Mytilus coruscus], Mytilus edulis, Mytilus galloprovincialis, Mytilus californianus, Mytilus trossulus, Protothaca (=Venerupis) staminea, Venerupis (=Tapes) philippinarum [Ruditapes philippinarum], Saxidomus giganteus, Nuttallia obscurata and Crepidula fornicata. In British Columbia, Canada, M. orientalis tends to prefer the mussel as a host and there is a high correlation between areas where this parasite occurs and where oyster seed from Japan was planted (Quayle 1988). Also in British Columbia, Marshall et al. (2003) reported a considerably higher prevalence in the varnish clam (N. obscurata, 60% to 64% infested) than in native littleneck clams (P. staminea, 8% to 4%) and Manila clams (V. philippinarum, 0% to 4%) obtained from the same beaches. In various locations in San Francisco and Humboldt bays, California, and in Puget Sound, Washington, USA, the prevalence of infestation in mussels (36.9% to 73.6% infested) was considerably greater than in O. lurida (0% to 9.6% infested) (Odlaug, 1946; Bradley and Siebert, 1978). The prevalence of infection was also high (65%) in the California mussel Mytilus californianus (Chew et. al, 1964). No associated bivalve mortality was reported in any of these cases.
DistributionTop of page
The current wide distribution of Mytilicola orientalis in the northern hemisphere is clearly a result of oyster aquaculture. Specifically, the extensive transplanting of Crassostrea gigas has carried this intestinal parasitic copepod with it. Local (regional) distribution at least throughout the Northeastern Pacific, and probably elsewhere, seems restricted to sheltered muddy estuaries, where bivalves near the low tide mark seem to be most heavily infested. Goater and Weber (1996) attributed this distribution to factors that restrict colonization by the free-swimming larvae, suggesting that wave action, tidal currents, salinity and/or substratum conditions may play a role.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Atlantic, Northeast||Present||Introduced||1992||Streftaris et al., 2005||North Sea|
|Mediterranean and Black Sea||Present||Introduced||1979||Streftaris et al., 2005||Mediterranean Sea, area not specified|
|Pacific, Northeast||Widespread||Introduced||Lauckner, 1983|
|Pacific, Northwest||Present||Native||Mori, 1935||Inland Sea of Japan.|
|Japan||Present||Native||Mori, 1935||Inland Sea of Japan (Japanese Seto-Naikai)|
|Canada||Present||Present based on regional distribution.|
|-British Columbia||Present||Introduced||Bernard, 1969; Bower et al., 1992; Goater and Weber, 1996; Marshall et al., 2003|
|USA||Present||Present based on regional distribution.|
|-California||Present||Introduced||Chew et al., 1964; Chew et al., 1965; Katkansky et al., 1967; Bradley and Siebert, 1978|
|-Oregon||Present||Introduced||Chew et al., 1965; Katkansky et al., 1967||Yaquina Bay|
|-Washington||Present||Introduced||Odlaug, 1946; Sparks, 1962; Chew et al., 1965; Katkansky et al., 1967|
|France||Present||Introduced||Deslou-Paoli, 1981; Lauckner, 1983; Grizel, 1985; Holmes and Minchin, 1995|
|Ireland||Present||Introduced||Minchin et al., 1993; Grave et al., 1995; Holmes and Minchin, 1995; Steele and Mulcahy, 2001|
|Netherlands||Present||Introduced||1993||Stock, 1993||Schelphoek (East Scheldt) 51° 33'N, 3° 36'E|
PathologyTop of page
Although bivalve infestation has been referred to as the disease mytilicoliasis (Elston 1993), the pathological effects of M. orientalis are controversial. It has been reported to cause adverse effects in the condition index (condition factor) of Ostrea lurida [Ostrea conchaphila] and Crassostrea gigas at several locations along the west coast of the United States (Odlaug, 1946; Chew et al., 1965; Katkansky et al., 1967; Lauckner 1983). However, Odlaug (1946) noted that spawning in O. lurida caused a greater reduction in condition factor than that caused by M. orientalis infestation. Other reports indicated that the survival of infested oysters was not affected and there was little evidence of reduction in shell growth (Chew et al., 1965; Katkansky et al., 1967). More recent publications reported minimal impact of M. orientalis on the various species of hosts on the west coast of Canada and in Europe. Deslou-Paoli (1981) detected a difference in the condition index of C. gigas from Marennes-Oléron Basin, France, only during the spring and the autumn when the oysters were under stress from low food availability or spawning, and he suggested that oysters in good condition may reject the parasite. Bernard (1969) and De Grave et al. (1995) did not detect a decrease in the condition index of C. gigas infested with M. orientalis from coastal British Columbia, Canada and Dungarvan Bay, Ireland, respectively. Steele and Mulcahy (1999; 2001) detected no effect on condition, growth, sex or stage of glycogen content of C. gigas in Ireland, but did report a correlation with shell burrowing by the polychaete annelid Polydora sp.. Marshall et al. (2003) did not detect a significant impact on clams from the Strait of Georgia, British Columbia. However, in all these recent publications, the prevalence and intensity of infestation tended to be low. De Grave et al. (1995) noted that although far higher intensities of M. orientalis were recorded in the earlier studies, none quantified the exact relationship between the condition of the oysters and intensity of M. orientalis infestation. De Grave et al. (1995) concluded that at low levels of infestation, M. orientalis does not cause a lowering of the condition index of infested C.gigas. Nevertheless, M. orientalis is considered as a serious pest by some scientists (Holmes and Minchin, 1995; Streftaris and Zenetos, 2006).
DiagnosisTop of page
List of Symptoms/SignsTop of page
|Molluscs / Condition: watery - Soft-tissue Surfaces||Sign|
|Molluscs / Tissue erosion - Soft-tissue Surfaces||Sign|
EpidemiologyTop of page
The life cycle of Mytilicola orientalis is not known but is probably like that of M. intestinalis (Cheng, 1967; Goater and Weber, 1996). In California and Oregon, M. orientalis showed continuous reproductive activity (Katkansky et al., 1967; Bradley and Siebert, 1978) while in British Columbia, there was a single reproductive period from June to late August and larval stages were in the water column for a short period and did not travel far (Bernard, 1969). Sparks (1962) reported two reproductive peaks for M. orientalis in Washington State, one in the early spring and the other in late summer, and suggested that this parasite is incapable of maintaining itself in the gut of C. gigas for prolonged periods or that its life span is quite short. In France, Deslou-Paoli (1981) detected M. orientalis all year in the Marennes-Oléron Basin with greater infestation intensity (number of copepods per host) in the spring and a peak infestation in the autumn; the oysters first became infested when about six months old. The intensity of infestation tends to be relatively low with usually less than 10 M. orientalis per host, and larger hosts accommodating the most copepods (Deslou-Paoli, 1981; De Grave et al., 1995; Goater and Weber, 1996; Steele and Mulcahy, 2001).
Impact SummaryTop of page
|Fisheries / aquaculture||Negative|
ImpactTop of page
The speculations of negative economic impact on bivalve farming by Mytilicola orientalis suggested by some scientists have not yet materialized, but there is concern about possible negative synergy between the two species of Mytilicola (i.e. M. intestinalis and M. orientalis) affecting bivalve aquaculture in Europe.
Disease TreatmentTop of page
No treatment has been described. However, the treatment described by Blateau (1989) and Blateau et al. (1992) for Mytilicola intestinalis (immersion of infested bivalves in a 30 mg/l concentration of the organophosphorate Dichlorvos for 2 hr) may also be effective against Mytilicola orientalis.
Prevention and ControlTop of page
Husbandry Methods and Good Practice
ReferencesTop of page
Blateau D, 1989. [English title not available]. (Expériences de traitement des moules (M. edulis) de bouchots de la Baie du Mont Saint-Michel parasitées par Mytilicola intestinalis - Septembre 1987 et 1988.) Expériences de traitement des moules (M. edulis) de bouchots de la Baie du Mont Saint-Michel parasitées par Mytilicola intestinalis - Septembre 1987 et 1988., France: Ifremer, 17 pp. http://www.ifremer.fr/docelec/doc/1989/rapport-1943.pdf
Bower SM; Blackbourn J; Meyer GR, 1992. Parasite and symbiont fauna of Japanese littlenecks, Tapes philippinarum (Adams and Reeve, 1850), in British Columbia. Journal of Shellfish Research, 11(1):13-19.
Chew KK; Sparks AK; Katkansky SC, 1965. Preliminary results on the seasonal distribution of Mytilicola orientalis and the effect of this parasite on the condition of the Pacific oyster, Crassostrea gigas. Journal Fisheries Research Board of Canada, 22(4):1099-1101.
Dare PJ, 1982. The susceptibility of seed oysters of Ostrea edulis L. and Crassostrea gigas Thunberg to natural infestation by the copepod Mytilicola intestinalis Steuer. Aquaculture, 26(3-4):201-211.
Deslou-Paoli JM, 1981. Mytilicola orientalis Mori, Crassostrea gigas Thunberg's parasite, in the basin of Marennes-Oleron: impact on the condition and the biochemical composition of oysters during rearing. Mytilicola orientalis Mori, Crassostrea gigas Thunberg's parasite, in the basin of Marennes-Oleron: impact on the condition and the biochemical composition of oysters during rearing. International Council for the Exploration of the Sea, Shellfish and Benthos Committee, 16 pp. http://www.ifremer.fr/docelec/doc/1981/acte-2938.pdf
Goater CP; Weber AE, 1996. Factors affecting the distribution and abundance of Mytilicola orientalis (Copepoda) in the mussel, Mytilus trossulus, in Barkley Sound, B.C. Journal of Shellfish Research, 15(3):681-684.
Grave S de; Xie Q; Casey D, 1995. The intensity of infestation by the intestinal copepod, Mytilicola orientalis, does not affect the condition of Pacific oysters (Crassostrea gigas). Bulletin of the European Association of Fish Pathologists, 15(4):129-131.
Grizel H, 1985. Mytilicola orientalis Mori, parasitism. (Parasitose à Mytilicola orientalis Mori.) Identification Leaflets for Diseases and Parasites of Fish and Shellfish, 20:4 pp. http://www.ices.dk/products/fiche/Disease/2006/Sheet%20no%2020.pdf
ICES, 2004. ICES Code of Practice on the Introductions and Transfers of Marine Organisms 2004. ICES Code of Practice on the Introductions and Transfers of Marine Organisms 2004. Copenhagen, Denmark: International Council for the Exploration of the Sea, 29 pp. http://www.ices.dk/reports/general/2004/ICESCOP2004.pdf
Katkansky SC; Sparks AK; Chew KK, 1967. Distribution and effects of the endoparasitic copepod, Mytilicola orientalis, on the Pacific oyster Crassostrea gigas on the Pacific coast. Proceedings of the National Shellfisheries Association, 57:50-58.
Katkansky SC; Warner RW, 1968. On the unusual occurrence of the Copepod Mytilicola orientalis in the digestive diverticulae of the Pacific Oyster, Crassostrea gigas. Journal of Invertebrate Pathology, 12(3):475-476.
Lauckner G, 1983. Diseases of Mollusca: Bivalvia. In: Diseases of Marine Animals. Vol II: Introduction, Bivalvia to Scaphoda [ed. by Kinne O]. Hamburg, Germany: Biologische Anstalt Helgoland, 477-961.
Marshall WL; Bower SM; Meyer GR, 2003. A comparison of the parasite and symbiont fauna of cohabiting native (Protothaca staminea) and introduced (Venerupis philippinarum and Nuttalia obscurata) clams in British Columbia. Journal of Shellfish Research, 22(1):185-192.
Minchin D; Duggan CB; Holmes JMC; Neiland S, 1993. Introductions of exotic species associated with Pacific oyster transfers from France to Ireland. Copenhagen, Denmark: International Council for Exploration of the Sea, 11 pp. [ICES Committee Meetings Documents, CM 1993(F:27).]
Sparks AK, 1962. Some preliminary observations on the incidence of infection and pathological effect of the parasitic copepod, Mytilicola orientalis Mori, in the Pacific oyster (Crassostrea gigas (Thunberg)) on the west coast of the United States. Some preliminary observations on the incidence of infection and pathological effect of the parasitic copepod, Mytilicola orientalis Mori, in the Pacific oyster (Crassostrea gigas (Thunberg)) on the west coast of the United States, 139. International Council for Exploration of the Sea, Shellfish Committee, 1-9.
Steuer A, 1902. Mytilicola intestinalis n. gen. n. sp. from the intestine of Mytilus galloprovincialis Lam. (Mytilicola intestinalis n. gen. n. sp. aus dem Darme von Mytilus galloprovincialis Lam.) Zoologischer Anzeiger, 25:635-637.
Streftaris N; Zenetos A; Papathanassiou E, 2005. Globalisation in marine ecosystems: the story of non-indigenous marine species across European seas. Oceanography and Marine Biology: An Annual Review, 43:419-453.
OrganizationsTop of page
World: International Council for the Exploration of the Seas - Working Group on Introduction and Transfers of Marine Organisms (ICES - WGITMO), H. C. Andersens Boulevard 44-46, DK-1553, Copenhagen V, Denmark, http://www.ices.dk/workinggroups/ViewWorkingGroup.aspx?ID=33
World: International Council for the Exploration of the Seas - Working Group on Pathology and Diseases of Marine Organisms (ICES - WGPDMO), H. C. Andersens Boulevard 44-46, DK-1553, Copenhagen V, Denmark, http://www.ices.dk/workinggroups/ViewWorkingGroup.aspx?ID=169
ContributorsTop of page
09/10/09 Original text by:
Susan Bower, Department of Fisheries and Oceans, Biological Sciences Branch, Pacific Biological Station, Nanaimo, British Colombia V9R 5K6, Canada
Distribution MapsTop of page
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