Argulus coregoni
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Ichthyostraca
Order: Arguloida
Family: Argulidae
Genus: Argulus
Species:
A. coregoni
Binomial name
Argulus coregoni
Thorell, 1865

The carp louse Argulus coregoni is an obligate ectoparasitic branciuran species on fish.[1] It occurs in China and Japan,[2] and Scandinavia.[1] Argulus coregoni can pose a threat to fish kept in fish farms.[3][4]

Life cycle

Argulus coregoni has a direct life cycle, meaning that the parasite is transmitted between individuals of the same host species without an intermediate host. At Northern latitudes, adults do not survive winter, but only the eggs attached to rocks survive throughout the winter.[1] Egg hatching occurs in May[1][2] once water temperatures exceed 10 °C.[3] From the eggs, metanauplii emerge which actively search for a fish host to feed on.[5] These can survive up to two days without finding a host.[4] One or two generations can be completed each year, depending on environmental conditions.[3] This means that infection rates of host typically reach their peak during the summer months.[2] Females start laying eggs from July until the end of summer.

Although some differences are seen in the development between males and females, the adults generally have the same size 9–12 mm (0.4–0.5 in). This is in contrast with other dioecious crustacean species[6] The sex ratio — the ratio between males and females in the population — is generally close to 1:1,[3][6] as expected for sexually reproducing species under Fisher's principle. Both sexes can detach from the host and find alternative hosts. However, this behaviour is more common in males as they can also switch between hosts to search for mates.[6]

Host species

Argulus coregoni mainly infect salmonids, such as rainbow trout and brook trout.[2][3] It is, however, also able to infect other species of fish, such sweet fish.[7] This is supported by evidence that larvae can successfully develop on both salmonids and cyprinids, but developmental rate and reproductive output on the latter host group is reduced.[8]

In choice experiments it shows increased host preference with maturation,[7] this likely reflects the better development on its normal salmonid hosts.

Distribution

On the host

Argulus coregoni aggregate on specific parts of their hosts. The prefer attaching near the fins, in particular the pectoral and pelvic fins. Larger individuals are found towards the head of the host, but not on the head.[2] To move from one host to another it can swim freely in water column.[9] Adults can survive up to two weeks without feeding on a fish host.[4]

Typical sites where Argulus coregoni can be found on salmonoid hosts. Based on Shimura (1983).[2]

Argulus coregoni attaches itself to the host with suckers (maxillae) and hooks. The latter are abundant on the underside of the body. The suckers are used to tear the host skin. A. coregoni feed on the blood and mucus from the resulting wound.[4]

They bury their bodies into the scale pockets [9] and their flattened body shape allows them to sit closely against the body of the host, minimising drag and the risk of detachment.[10] The eggs of gravid females protrude from the fish scales.[9]

In the host population

Like many ectoparasites, A. coregoni shows aggregation within the host population.[11] This means that some host individuals carry many parasites, but that most only carry a few. This appears to be due to differences in exposure rather than in susceptibility.[11] Indeed, it appears that host behaviour plays an important role in exposure and that certain hos behaviours make them more susceptible to infections.[12]

Symptoms

Infected fish can show a range of symptoms, especially at heavier infections. The symptoms include scales peeling off, red spots at the site of infection, and reduced growth rates.[9] Fish can become weak, but Argulus coregoni does normally not cause host mortality.[9] In coinfections it can, however, increase host mortality in some host species.[13] Argulus coregoni infections do not lead to threats to natural fish populations. In fish farms the infections may case problems due to the lack of natural predators of the parasites, and the high density of fish.[4]

References

  1. 1 2 3 4 Mikheev, V.N.; Pasternak, A.F.; Valtonen, E.T.; Lankinen, Y. (2001). "Spatial distribution and hatching of overwintered eggs of a fish ectoparasite, Argulus coregoni (Crustacea: Branchiura)". Diseases of Aquatic Organisms. 46 (2): 123–128. doi:10.3354/dao046123. PMID 11678227.
  2. 1 2 3 4 5 6 Shimura, S. (1983). "Seasonal occurrence, sex ratio and site preference of Argulus coregoni Thorell (Crustacea: Branchiura) parasitic on cultured freshwater salmonids in Japan". Parasitology. 86 (3): 537–552. doi:10.1017/S0031182000050721. S2CID 85360437.
  3. 1 2 3 4 5 Hakalahti, T.; Valtonen, E.T. (2003). "Population structure and recruitment of the ectoparasite Argulus coregoni Thorell (Crustacea: Branchiura) on a fish farm". Parasitology. 127 (1): 79–85. doi:10.1017/S0031182003003196. PMID 12885191. S2CID 25800328.
  4. 1 2 3 4 5 Suárez-Morales, E. (2015). "Chapter 29 - Class Maxillopoda". In Thorp, J.H.; Covich, A.P. (eds.). Thorp and Covich's Freshwater Invertebrates (Fourth ed.). Academic Press. pp. 709–755. doi:10.1016/B978-0-12-385026-3.00029-2. ISBN 978-0-12-385026-3.
  5. ↑ Hakalahti, T.; Karvonen, A.; Valtonen, E.T. (2006). "Climate warming and disease risks in temperate regions – Argulus coregoni and Diplostomum spathaceum as case studies". Journal of Helminthology. 80 (2): 93–98. doi:10.1079/JOH2006351. S2CID 7449570.
  6. 1 2 3 Pasternak, A.F.; Mikheev, V.N.; Valtonen, E.T. (2004). "Adaptive significance of the sexual size dimorphism in the fish ectoparasite Argulus coregoni (Crustacea: Branchiura)". Doklady Biological Sciences. 399 (1–6): 477–480. doi:10.1007/s10630-005-0017-x. PMID 15717613. S2CID 23008098.
  7. 1 2 Mikheev, V.N.; Pasternak, A.F.; Valtonen, E.T. (2007). "Host specificity of Argulus coregoni (Crustacea: Branchiura) increases at maturation". Parasitology. 134 (12): 1767–1774. doi:10.1017/S0031182007003125. PMID 17626688. S2CID 12937260.
  8. ↑ Pasternak, A.; Mikheev, V.; Valtonen, E.T. (2004). "Growth and development of Argulus coregoni (Crustacea: Branchiura) on salmonid and cyprinid hosts". Diseases of Aquatic Organisms. 58: 203–207. doi:10.3354/dao058203. PMID 15109143.
  9. 1 2 3 4 5 Kar, D. (2016). "Introduction". Epizootic Ulcerative Fish Disease Syndrome. Elsevier. pp. 1–19. doi:10.1016/B978-0-12-802504-8.00001-8. ISBN 978-0-12-802504-8.
  10. ↑ Meehan, O.L. (1940). "A review of the parasitic Crustacea of the genus Argulus in the collections of the United States National Museum". Proceedings of the United States National Museum. 88 (3087): 459–522. doi:10.5479/si.00963801.88-3087.459.
  11. 1 2 Bandilla, M.; Hakalahti, T.; Hudson, P.J.; Valtonen, E.T. (2005). "Aggregation of Argulus coregoni (Crustacea: Branchiura) on rainbow trout (Oncorhynchus mykiss): a consequence of host susceptibility or exposure?". Parasitology. 130 (2): 169–176. doi:10.1017/S0031182004006407. PMID 15727066. S2CID 16253111.
  12. ↑ Mikheev, V.N.; Mikheev, A.V.; Pasternak, A.F.; Valtonen, E.T. (2000). "Light-mediated host searching strategies in a fish ectoparasite, Argulus foliaceus L. (Crustacea: Branchiura)". Parasitology. 120 (4): 409–416. doi:10.1017/S0031182099005569. PMID 10811282. S2CID 36738198.
  13. ↑ Bandilla, M.; Valtonen, E.T.; Suomalainen, L.R.; Aphalo, P.J.; Hakalahti, T. (2006). "A link between ectoparasite infection and susceptibility to bacterial disease in rainbow trout". International Journal for Parasitology. 36 (9): 987–991. doi:10.1016/j.ijpara.2006.05.001. PMID 16750536.
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