Salmincola californiensis
(Dana, 1853)
Common Name:
Gill maggot
Synonyms and Other Names:
Gill lice, a copepod, Salmincola beani WIlson 1908, Achtheres carpenteri Packard 1874, Lernaeopoda californiensis Dana 1852, Lernaeopoda beani Wilson 1908, Lernaeopoda falculata Wilson 1908, Salmincola bicauliculata Wilson 1908, Salmincola falculata Wilson 1908, Salmincola lata Markevich 1940
Identification:
Salmincola californiensis has a life cycle with 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 californiensis copepodids are differentiated from other Salmincola spp. by its second antenna morphology as described by Ruiz et al. (2017). The copepodid can be light brown or tan in color. The chalimus and adult forms 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. 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 and Cousens (1973) and Ruiz et al. (2017). Salmincola californiensis in all three forms can be found on the gills, skin, and fins of infested fish.
Size:
Adult female is 4.0 to 4.6 mm in length (Ruiz et al. 2017), excluding the egg case which ranges from 2 to 9 mm in length (Murphy et al. 2020a). Adult male is 1.06 to 1.24 mm long. Copepodid larvae are 0.66 to 0.72 mm in length (Kabata and Cousens 1973).
Native Range:
Not well documented (Wilson 1915), but S. californiensis was originally confined to salmonids in tributaries of the northern Pacific Ocean and likely mimic the native ranges of Oncorhynchus spp. (Piasecki et al. 2004).
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This map only depicts Great Lakes introductions.
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Great Lakes Nonindigenous Occurrences:
Salmincola californiensis is found in Lake Erie since the 1980’s (Jason Detar, personal communication, December 18, 2020) and more recently in Lake Ontario in 2014 (Mullin and Reyda 2020).
Ecology:
Salmincola californiensis, a Lernaopodid copepod, parasitizes Pacific Salmon and Trout primarily of the genus Oncorhynchus (Wilson 1915; Kabata and Cousens 1973). It has seven distinct stages of development: a brief immobile naupliar stage, a free-swimming copepodid, four chalimus stages, and an adult form. After hatching, an immobile nauplius emerges and molts into a swimming copepodid within 30 minutes. Copepodids roam the water column in search of a host for up to 18 days before mortality, with survival time decreasing with increasing temperature (Murphy et al. 2020a). 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, molting between each of the four forms. In the fourth chalimus, females detach their frontal filament and begin excavating another hole for a final molt 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 molt 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 molts 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 via the bulla, a fertilized adult female will produce pairs of egg sacs multiple times in a season with re-fertilization, and can live on a host fish for years. Females produce 21–368 eggs per egg sac which hatch after 2–25 days. Number of eggs per female increases with temperature while time to hatch decreases (Vigil et al. 2015; Murphy et al. 2020b). The full life cycle of S. californiensis from egg to adult is 60–75 days (Kabata and Cousens 1977).
All life stages of S. californiensis can withstand a range of temperatures, from at least 4–21?, with greater survival at lower temperatures. However, fish parasitism rates are lower at lower temperatures due to decreased swimming speed and activity of the copepodid. The optimum temperature for successful S. californiensis parasitism is estimated to be similar to that of its hosts, Oncorhynchus spp., 12–19? (Richter and Kolmes 2005), at which rates are expected to be the highest.
Salmincola californiensis has been recorded to parasitize the following species: Rainbow (Oncorhynchus mykiss), Lake (Salvelinus namaycush), and Cutthroat Trout (O. clarki), Sockeye (O. nerka), Chinook (O. tshawytscha), Masu (O. masou), and Coho Salmon (O. kisutch) (Arai and Mudry 1983; Nasagawa and Urawa 2002; Barndt and Stone 2003; Monzyk et al. 2015). The site of 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 and/or lotic fish are typically infected (Kabata and Cousens 1977; Monzyk et al. 2015). The number of parasites per fish also increases with fish length (Barndt and Stone 2003).
Means of Introduction:
Salmincola californiensis has been documented to parasitize Rainbow Trout in Lake Erie beginning in the 1980’s (Jason Detar, personal communication, December 18, 2020). It was later discovered in an eastern Lake Ontario tributary in 2014 by fishermen and fisheries managers in the Salmon River (Figura 2014). Salmincola californiensis was likely introduced to the Great Lakes region as a hitchhiker with infected hatchery fish transported from the west coast and stocked in the lakes and their tributaries (Mullin and Reyda 2020).
Status:
Established in Lake Erie and Lake Ontario.
Great Lakes Impacts:
Salmincola californiensis has a high environmental impact in the Great Lakes. Realized:
Around 70% (n = 120) of Rainbow Trout and 39% (n = 223) of Chinook Salmon caught in Lake Ontario were infected with S. californiensis. The rate of infection in Lake Ontario Rainbow Trout was two times that of the rate in their native range (Mullin and Reyda 2020).
The mechanical action by which S. californiensis 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 sustainable 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:
Salmincola californiensis has been recorded to parasitize the following species, all of which are present in the Great Lakes: Rainbow Trout (O. mykiss), Lake Trout (Salvelinus namaycush), Chinook Salmon (O. tshawytscha), and Coho Salmon (O. kisutch) (GLMRIS 2012).
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 Chinook Salmon in a laboratory study was greatly diminished by S. californiensis and fatigue greatly increased, which suggests that gill infestation reduces gas exchange and osmotic regulation (Pawaputanon 1980; Herron et al. 2018). The osmotic imbalance can lead to anemia and increased blood clotting (Pawaputanon 1980). Secondary viral, fungal, or bacterial infections may also be more prevalent where S. californiensis is attached (Bandilla et al. 2006). Further, parasitism by S. californiensis decreased egg production by Rainbow Trout in a California hatchery (Gall et al. 1972). Parasitized juvenile Sockeye Salmon were also less able to cope with environmental stress and had increased mortality as temperatures rose above 21? in laboratory settings (Pawaputanon 1980).
A telemetry study of Chinook Salmon in a reservoir indicated a slight increase in short-term mortality (within 24 hours of tagging) as well as negative effects on fish movements in fish infested with S. californiensis (Beeman et al. 2015).
Salmincola californiensis has a moderate socio-economic impact in the Great Lakes.
Potential:
Lernaeopodids including S. californiensis were historically damaging to salmon hatcheries (Wilson 1915). Modern hatcheries are also negatively impacted by S. californiensis, and many are enacting control measures to limit damage (Modin and Veek 2002; Rash et al. 2017). Many of the fish species that S. californiensis infects (Chinook Salmon, Coho Salmon, Lake Trout, and Rainbow Trout) 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 californiensis 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 certification of salmonids for the presence of S. californiensis (PAFBC 2019).
Control
Biological
Brook Trout (Salvelinus fontinalis) were held upstream of a Rainbow Trout hatchery which prevented the majority of S. californiensis copepodids from entering and infecting Rainbow Trout. The exact reason that Brook Trout prevented the passage of S. californiensis is unknown, but it is speculated that their gills are unsuitable for the reproduction of S. californiensis thereby reducing the parasite’s population numbers (Modin and Veek 2002).
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 S. californiensis 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
Feed medicated with 0.2% emamectin benzoate (50 µg kg−1d−1 for 7 consecutive days) has been shown to be effective in reducing S. californiensis infestations in Rainbow Trout (Oncorhynchus mykiss) without adverse effects on the fish (Bowker et al. 2012; Gunn et al. 2012).
Orally intubating Rainbow Trout and Chinook Salmon with 0.2 mg ivermectin kg-1 fish also proved effective in eradicating adult and embedded S. californiensis without damaging gill structure (Johnson and Heindel 2001; Roberts et al. 2004).
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.
References
(click for full reference list)
Other Resources:
Author:
Bartos, A.
Contributing Agencies:
Revision Date:
7/14/2022
Peer Review Date:
6/8/2021
Citation for this information:
Bartos, A., 2024, Salmincola californiensis (Dana, 1853): 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=3247, Revision Date: 7/14/2022, Peer Review Date: 6/8/2021, 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.