Salmincola edwardsii
(Olsson, 1869)
Common Name:
Gill louse
Synonyms and Other Names:
A gill maggot, Lernaeopoda edwardsii Olsson 1869, Lernaeopoda fontinalis Smith 1874, Lernaeopoda arcturi Miers 1877, Lernaeopoda bicauliculata (Wilson 1908), Salmincola oquassa Wilson 1915, Salmincola exsanguinata Sandeman and Pippy 1967
Identification:
Salmincola edwardsii’s life cycle has three distinct forms: a copepodid, chalimus, and adult. The copepodid is oval in shape, with a transverse constriction at midlength. It has two pairs of swimming legs on the forebody and a pair of vestigial legs near the rear. It has two antennas, with the second divided into two branches. The upper and lower lip are partially fused, and the mandible is short, pointed, and blade-like with no teeth. Salmincola edwardsii copepodids are differentiated from other Salmincola spp. by its second antenna morphology, as described by Ruiz et al. (2017) and adults are typically smaller than those of S. californiensis (Kabata 1969). The copepodid can be light brown or tan in color. The chalimus and adult forms of S. edwardsii are similar to each other in morphology and visual appearance to the unaided eye. Both are oblong in shape, possess similar appendages, and are opaque white in color. The chalimus attach to the exterior of the fish using their second maxillary and frontal filament and adult females are attached by a conical bulla (attachment organ). Adult females are twice as large as males and can have a pair of egg sacs with visible spherical eggs. Further description can be found in Kabata (1969) and Ruiz et al. (2017). Salmincola edwardsii in all three forms can be found on the gills, skin, and fins of infested fish.
Size:
Adult female is 1.6 to 3.7 mm in length, excluding the egg case which ranges from 1.2 to 2.3 mm in length (Conley and Curtis 1994; Ruiz et al. 2017). Copepodid larvae are around 0.73 mm in length (Fasten 1912).
Native Range:
Distributed across the northern hemisphere’s Atlantic Rim. Distinct variants are divided amongst the Nearctic (North America) and Palearctic (Eurasia) regions (Ruiz et al. 2017). Native range likely mimics those of host Salvelinus spp. (Kabata 1969), and as such may be native to some parts of the Great Lakes region. Salmincola edwardsii has been recorded in the U.K. (Fryer 1981), Greenland (Due and Curtis 1995), Iceland (Kristmundsson and Richter 2009), Norway (e.g., Sobecka and Piasecki 1993; Amundsen et al. 1997; Paterson et al. 2019), Finland (Boxshall 2020), Sweden (Boxshall 2020), Germany (Boxshall 2020), Poland (Boxshall 2020), Russia (Shedko and Shedko 2002), Japan (Nagasawa 2020), northeastern Canada (e.g., Black et al. 1983; White et al. 2020), and throughout the northeastern U.S.A. (e.g., Muzzall 1986; Ruiz et al. 2017; Mitro and Griffin 2018). The exact range is not well defined in North America, however, S. edwardsii was presumed indigenous to Wisconsin streams (Fasten 1912).
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This map only depicts Great Lakes introductions.
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Great Lakes Nonindigenous Occurrences:
Recorded in 14% of Brook Trout (Salvelinus fontinalis) (n=22) captured in Lake Huron and its tributaries between 1961–1971 (Nepszy 1988). Also found in Brook Trout in Lake Superior between 2005–2017 (Boone and Quinlan 2019). Salmincola edwardsii was recorded across Michigan streams (Muzzall 1986), lakes (Muzzall 1984), and fish farms (Muzzall 2000). The earliest record of S. edwardsii in Michigan was in 1894 from the ponds of the U.S. Fish Commission Station in Northville, Michigan. Also found in hatcheries in Wisconsin, New York, Minnesota and Maine in the early 1900’s (Wilson 1915). No specimens on record from the southeastern United States until their discovery in a trout farm connected to Watauga Rover, North Carolina in 2014 (Ruiz et al. 2017).
Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Salmincola edwardsii are found here.
Table last updated 4/27/2024
† Populations may not be currently present.
* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).
Ecology:
Salmincola edwardsii, a Lernaopodid copepod, parasitizes trout primarily of the genus Salvelinus (Kabata 1969). It has seven distinct stages of development: a brief naupliar stage, a free-swimming copepodid, four chalimus stages, and an adult form. After hatching, a nauplii emerges and moults into a swimming copepodid. Copepodids roam the water column in search of a host for up to one month before mortality, with survival time decreasing with increasing temperature (Conely and Curtis 1993). Once a suitable host is found, the copepodid lands on the skin, fins, and gills of the fish and excavates a hole in search of solid subdermal support for attachment. Once support is found and a suitable size hole is made, it uncoils its frontal filament and cements itself to the fish using secretions from its frontal gland. The copepodid then begins to enter the chalimus stage, moulting between each of the four forms. In the fourth chalimus, females detach their frontal filament and begin excavating another hole for a final moult into the adult form. At any time from the fourth form and through adulthood, females can be fertilized by adult males, who instead detach from the fish after their final moult in search of a mate. Adult males die soon after mating. Once the female excavates the new hole in the host fish, it reattaches with the maxillipeds and moults into the adult stage.
The adult female everts a bulla and implants it into the excavated hole, after which it attaches to the bulla with its manubrium to absorb nutrients and remain until death (Kabata and Cousens 1973). Once attached to the bulla, a fertilized adult female will produce pairs of egg sacs multiple times in a season, and can live on a host fish for years. Females produce between 36–87 eggs per egg sac which typically hatch within 2 days. Number of eggs per female increases with temperature but decreases sharply once above 16º(Conley and Curtis 1993). Photoperiod length has no effect on hatch initiation or hatching rate (Poulin et al. 1990; Conley and Curtis 1993).
Salmincola edwardsii has been recorded to parasitize the following species: Prosopium williamsoni (Mountain Whitefish), Salvelinus mala (Dolly Varden Trout), S. namaycush (Lake Trout), S. fontinalis (Brook Trout), and S. alpinus (Arctic Charr) (Beverly-Burton 1978; Arai and Mudry 1983). The site of a Salmincola spp. attachment varies with fish size and habitat. Small and/or lentic fish are often infected on body surfaces and fins, while the brachial cavity of larger (>300 mm) and/or lotic fish are typically infected (Kabata and Cousens 1977; Black 1982; Monzyk et al. 2015). The number of parasites per fish also increases with fish length and age (Hare and Frantsi 1974; Barndt and Stone 2003).
Means of Introduction:
Salmincola edwardsii can be spread from the transport of stocked Salvelinus spp. that are infested with the parasite or through the natural dispersal of a fish host throughout a waterbody. Warmer spring temperatures due to climate change are also promoting the range expansion, intensity, and maximum prevalence of S. edwardsii, particularly in Wisconsin streams (Mitro and Griffin 2018).
Status:
Cryptogenic. Reproducing and overwintering in Lake Huron and Lake Superior.
Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...
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Salmincola edwardsii has a high environmental impact in the Great Lakes. Realized:
Salmincola edwardsii was recorded in 14% of Brook Trout (n=22) captured in Lake Huron and its tributaries between 1961–1971 (Nepszy 1988). It was also found in Brook Trout in Lake Superior between 2005–2017 (Boone and Quinlan 2019).
The mechanical action by which Salmincola spp. attaches and burrows into a fish can cause extensive tissue damage. The epithelium is the most extensively damaged tissue, typically resulting in severe gill injuries (Kabata and Cousens 1977). If a female fails to reach stainable support tissue when burrowing into a fish, it may continue to burrow into soft tissue and can eventually lead to the death of the fish (Kabata and Cousens 1977).
Potential:
Parasitized gill filaments were inflamed and their growth was inhibited in Rainbow Trout in a hatchery in Iowa (Sutherland et al. 1985). The swimming ability of parasitized fishes can be diminished by Salmincola spp. and fatigue can be greatly increased, which suggests that gill infestation reduces gas exchange and osmotic regulation (Pawaputanon 1980; Herron et al. 2018). An osmotic imbalance can lead to anemia and increased blood clotting (Pawaputanon 1980). Secondary viral, fungal, or bacterial infections may also be more prevalent where Salmincola spp. are attached (Bandilla et al. 2006).
Further, parasitization by Salmincola spp. can decrease egg production (Gall et al. 1972) and reduce the ability for a fish to cope with environmental stressors (Pawaputanon 1980). Brook Trout parasitized by S. edwardsii had reduced resistance to high temperatures (Vaughun and Coble 1975). Combined with the effects of climate change, S. edwardsii reduced recruitment of age-0 Brook Trout by 77–89% between 2012–2014, leading to their near extirpation from a Wisconsin stream (Mitro 2016).
Salmincola edwardsii has a moderate socio-economic impact in the Great Lakes.
Potential:
Lernaeopodids including S. edwardsii were historically damaging to salmon hatcheries (Wilson 1915). Modern hatcheries are also negatively impacted by S. edwardsii, and many are enacting control measures to limit damage (Duston and Cusack 2002).
Salmincola edwardsii commonly infects Brook Trout (Salvenius fontinalis) and Lake Trout (S. namaycush) and therefore may also infect the hybrid Splake (Salvelinus namaycush x fontinalis). Lake Trout, Brook Trout, and Splake are prevalent in the Great Lakes and negative impacts from infestations may harm commercial and recreational fishing (GLMRIS 2012).
There is little or no evidence to support that Salmincola edwardsii has significant beneficial effects in the Great Lakes.
Management:
Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species, however the Pennsylvania Fish and Boat Commission recently created a protocol for the certification of salmonids for the presence of S. edwardsii in shipments and facilities. Control
Biological
There are no known biological control methods for this species.
Physical
A mechanical filter can be used to filter out the 0.7 mm copepodids; however, in natural systems, these filters are quickly clogged (Mitchum 1995). Attached Salmincola spp. can be removed from infected fish manually by hand, but care must be taken to not damage the gill tissue (Johnson and Heindel 2001).
Chemical
Food pellets coated with Emamectin benzoate 0.2% were fed to S. edwardsii infested brook trout for 7 days at 50 μg-1 kg-1 body weight per day, resulting in a 40-60% reduction in the average number of attached adult females (Duston and Cusack 2002).
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.
Remarks:
This species' many synonyms are attributed to the inaccuracy of early descriptions (Kabata 1969).
References
(click for full reference list)
Other Resources:
Author:
Bartos, A., M.E. Neilson
Contributing Agencies:
Revision Date:
7/14/2022
Peer Review Date:
5/25/2021
Citation for this information:
Bartos, A., M.E. Neilson, 2024, Salmincola edwardsii (Olsson, 1869): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=2932, Revision Date: 7/14/2022, Peer Review Date: 5/25/2021, Access Date: 4/28/2024
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.