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| NAS - Nonindigenous Aquatic Species |
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Common Name: a microsporidian parasite
Synonyms and Other Names: disease known as microsporidiosis
Taxonomy: available through 
Identification:
The parasitic spores of G. hertwigi have thick cell walls with rough, wrinkled and loosely folded surfaces. The sporoplasm contains a nucleus and free ribosomes and is surrounded by a plasma membrane. It can be injected into a host cell via a thin polar tube, which is held coiled inside the spore until it is discharged. This tube is surrounded at the base by a polaroplast, or arrangement of membranes or vesicles. In the digestive tracks of host rainbow smelt (Osmerus mordax), cysts with up to 200 spores can form (Nakajima and Egusa 1979; Weidner et al. 1984; Scarborough-Bull and Weidner 1985; Pekcan-Hekim et al. 2005).
Spores are 3.5–5.5 μm by 1.5–2.6 μm in size. There is great variation but most populations fall at the larger end of the range. Smaller spores may be a specific variety of this species, proposed to be canadensis (Delisle 1969; Delisle 1972; Scarborough-Bull and Weidner 1985). Cysts range in size from 0.2–5 mm in diameter (Nepszy and Dechtiar 1972; Pekcan-Hekim et al. 2005).
Size: Spores are 3.5–5.5 μm by 1.5–2.6 μm in size. Cysts range in size from 0.2–5 mm in diameter.
Native Range: G. hertwigi was first recorded from smelt in the Baltic Sea and is considered native to Europe (Mills et al. 1993; Pekcan-Hekim et al. 2005).
Nonindigenous Occurrences: The first record of G. hertwigi in Lake Erie was in 1960. It subsequently occurred in Lake Ontario in 1968 (Chen and Power 1972).
Ecology: G. hertwigi typically infects euryhaline smelt species in the genus Osmerus but has also been recorded from pond smelt (Hypomesus olidus) and some Coregonus spp. It was originally known from marine environments but is now known to thrive in freshwater environments as well. Infection occurs via spores that enter through water taken in by the fish. The disease can be lethal or non-lethal and occurs first in the anterior digestive tract but can also arise in the posterior digestive tract, liver, pyloric caeca, heart, gonads and skin. Infections in the stomach and intestine can cause starvation and intestinal poisoning (Chen and Power 1972; Delisle 1972; Scarborough and Weidner 1979; Mills et al. 1993; Pekcan-Hekim et al. 2005).
The number of parasitic cysts in smelt populations can typically reach a peak from August through to September (although die-offs in Quebec typically occur in both spring and fall). Cyst growth may increase with increasing water temperature. However, since spores frequently enter both juvenile and adult fish at peak water temperatures, the largest cysts may not appear until after this time. Younger smelt appear more vulnerable to infection and older smelt may have increased immunity (Delisle 1969; Delisle and Veilleux 1969; Chen and Power 1972; Pekcan-Hekim et al. 2005).
G. hertwigi develops in the cytoplasm of host cells. It causes nuclear division without cytokinesis, resulting in one large cell up to 0.5–1 mm in diameter filled with many nuclei. Parasitic spores mature in a central vacuole in the enlarged host cell, undergoing schizogony, or asexual reproduction, many times. Once the spores have finished reproducing, the host cell ruptures and the parasites are eventually released into the water column to be ingested by new hosts. In new hosts, they attach to the digestive tract or other organs. The sporoplasm is then discharged from the spore case at high pressure, entering the host cell. The sporoplasm reorganizes before, during, and after ejection, and the resulting mass is larger than it was inside the spore case. Spore discharge can be triggered by a large change in pH to highly alkaline conditions (Wellings et al. 1969; Delisle 1972; Scarborough-Bull and Weidner 1985).
Means of Introduction: This parasite was introduced to the Great Lakes with its host, O. mordax, which in turn was introduced via stocking and/or dispersal through canal systems (Mills et al. 1993).
Status: Established where recorded.
Impact of Introduction:
A) Realized: Young-of-the-year O. mordax in Lake Erie have experienced high mortality rates in the past, very likely associated with the presence of G. hertwigi, apparent in 90% of distressed smelt examined (Nepszy et al. 1978). Samples taken in 1968 and 1969 in Lake Ontario and Lake Erie also indicated that G. hertwigi cysts in ovaries of mature females caused greatly reduced egg production (Chen and Power 1972). Die-offs in adults may occur as a result of the stress of high parasite loads during spawning.
On the other hand, during die-offs in Lake Erie in 1976 and 1977, the presence of G. hertwigi in rainbow smelt had no significant effect on fecundity or condition, although it did cause growth to slow somewhat (Nsembukya-Katuramu et al. 1981). No high density infestation events as large as those that occurred in the 1960s and 1970s have since been recorded from either Lake Erie or Lake Ontario (Mills et al. 1993).
B) Potential: None additional.
Remarks:
References
Chen, M. and G. Power. 1972. Infection of American smelt in Lake Ontario and Lake Erie with the microsporidian parasite Glugea hertwigi. Canadian Journal of Zoology 50(9):1183-1188.
Delisle, C. 1969. Biomonthly progress of a non-lethal infection by Glugea hertwigi in young-of-the-year smelt Osmerus eperlanus mordax. Canadian Journal of Zoology 47(5):871-876.
Delisle, C. E. 1972. Monthly variations of Glugea hertwigi (Sporozoa, Microsporidia) in different tissues and organs of the adult fresh water smelt and consequences of this infection on a massive annual mortality of this fish. Canadian Journal of Zoology 50(12):1589-1600.
Delisle, C. and C. Veilleux. 1969. Geographical distribution of rainbow smelts Osmerus eperlanus mordax and of Glugea hertwigi (Sporozoa, Microsporidia) in fresh waters of Quebec. Naturaliste Canadien (Quebec) 96(3):337-358.
Mills, E. L., J. H. Leach, J. T. Carlton and C. L. Secor. 1993. Exotic Species in the Great Lakes: A History of Biotic Crises and Anthropogenic Introductions. Journal of Great Lakes Research 19(1):1-54.
Nakajima, K. and S. Egusa. 1979. Surface pattern and size of spores of 3 species of the genus Glugea observed with a scanning electron microscope with special reference to a comparison between Glugea plecoglossi and Glugea sp. Fish Pathology 13(3):153-158.
Nepszy, S. J. and A. O. Dechtiar. 1972. Occurrence of Glugea hertwigi in Lake Erie rainbow smelt Osmerus mordax and associated mortality of adult smelt. Journal of the Fisheries Research Board of Canada 29(11):1639-1641.
Nepszy, S. J., J. Budd and A. O. Dechtiar. 1978. Mortality of young of the year rainbow smelt Osmerus mordax in Lake Erie associated with the occurrence of Glugea hertwigi. Journal of Wildlife Diseases 14(2):233-239.
Nsembukya-Katuramu, S., E. K. Balon and R. Mahon. 1981. A comparison of spawning harvested and die-off rainbow smelt Osmerus mordax in eastern Lake Erie, Canada. Journal of Great Lakes Research 7(2):144-154.
Pekcan-Hekim, Z., R. Rahkonen and J. Horppila. 2005. Occurrence of the parasite Glugea hertwigi in young-of-the-year smelt in Lake Tuusulanjarvi. Journal of Fish Biology 66(2):583-588.
Scarborough, A. and E. Weidner. 1979. Field and laboratory studies of Glugea hertwigi microsporidia in the rainbow smelt Osmerus mordax. Biological Bulletin (Woods Hole) 157(2):334-343.
Scarborough-Bull, A. and E. Weidner. 1985. Some properties of discharged Glugea hertwigi microsporidia sporoplasms. Journal of Protozoology 32(2):284-289.
Weidner, E., W. Byrd, A. Scarborough, J. Pleshinger and D. Sibley. 1984. Microsporidian spore discharge and the transfer of polaroplast organelle membrane into plasma membrane. Journal of Protozoology 31(2):195-198.
Wellings, S. R., L. E. Ashley and G. E. Mcarn. 1969. Microsporidial infection of English sole Parophrys vetulus. Journal of the Fisheries Research Board of Canada 26(8):2215-2218.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 4/18/2007 Citation for this information:
Rebekah M. Kipp. 2009. Glugea hertwigi. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=2368> Revision Date: 4/18/2007
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