Salmincola edwardsii

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Geographic Range

Salmincola edwardsii is found mainly in cold northern climates. It has a holarctic distribution and infects only fish of the genis Salvelinus. Salmincola edwardsii is limited to the locations that Salvelinus exists. A few places in which Salmincola edwardsii have been reported are northern North America, Britain, and Scandinavia. Common places for Salmincola edwardsii to exist are in rivers with free access to the sea. (Black, 1982)

Habitat

Salmincola edwardsii is found in aquatic habitats. The first larval stage of S. edwardsii swims in the water to find a host. Salmincola edwardsii need to be where its host genus Salvelinus lives, which is in lakes, and rivers that usually have outlets to the sea. Salmincola edwardsii spends most of its time near the bottom of the water column prior to attaching to a host. (Poulin, et al., 1990)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Although sexes of early larvae or chalimus stages are indeterminable until the latter part of the third larval stage, Salmincola edwardsii is a dioecious organism. This means there are sexually distinct female organisms and sexually distinct male organisms. The males are pygmies and after the last chalmius stage they move around in search of females. There is extreme sexual dimorphism in this species.

Salmincola edwardsii body structure is modified away from the ancestral copepod. In the adult all external signs of segmentation have disappeared. Adult females are permanently anchored to the host's flesh. They are attached by a structure called a "bulla". The bulla is nonliving. It is formed from head and maxillary gland secretions. This structure is the anchor that holds the female onto the host. The females of this family, Lernaeopodidae, are attached almost completely outside the host, which is different than most other parasitic copepod families. Salmincola edwardsii have huge maxillae that are fused to the bulla. Located and functioning anteriorly Salmincola edwardsii has modified maxillipeds for a grasping structure. The swimming legs and abdomen that is seen in most copepods is absent or vestigial in adult female Salmincola edwardsii.

Salmincola edwardsii is a relatively small organism. The average length of an adult male is 718.6 micrometers. The females are considerably larger averaging around 2055.8 micrometers. Size of the organism may be directly related to the site of attachment on the host fish. The gills of the fish offer protection and a more nutritious food supply; this location may support larger and more rapid development. The larvae are smaller than the adults approximately 512.4 micrometers. The adult female has an impermeable cuticle. (Conley and Curtis, 1992; Conley and Curtis, 1994; Roberts and Janovy, Jr, 2000)

  • Sexual Dimorphism
  • female larger
  • Range length
    718.6 to 2055.8 mm
    28.29 to 80.94 in

Development

Salmincola edwardsii are permanent ecotparasites. They have only a single host throughout their entire life cycle. There are four larval stages, called chalimus stages. The fifth stage of development is the adult. In each of the larval stages the organism grows larger. On a time scale of numbered days, from hatching out of the egg the chalimus I stage is found from day 0.5 to day 1.5, the chalimus II stage days 1-2.5, the chalimus III stage days 2-4. During the late periods of the chalimus III stage sex becomes determinable. The development after this point is different between male and female S. edwardsii. The male chalimus IV stage is found 2.5-5 days after hatching from the egg. Adult males are formed anywhere between 3-8 days. The females take more time to develop. The female chalimus stays in stage III longer than the male. She stays in stage III for up to 3-5.5 days after hatching. The IV chalimus stage is variable, existing anywhere from 4-20 days. The complete female adult does not develop until 13-20 days.

Adult males may live for up to 3 days at 13°C. Two weeks after Salmincola edwardsii's first contact with the host the adult female makes its final attachment. Larval development is variable due to the time the organism spends finding a host and a suitable attachment site. The adult female has a pair of identical egg sacs. The egg sacs are attached to the genital segment of her thorax, and rupture as soon as the egg hatches. The temperature of the water surroundings significantly affects the hatching time of the eggs. In warmer temperatures (until a point) the eggs will hatch sooner, (8-20°C was tested). The eggs can hatch in complete darkness. The first larval stage is free-living and non-feeding. The larva finds it host by swimming in the water and coming in contact with it. (Conley and Curtis, 1992; Conley and Curtis, 1994; Poulin, et al., 1989; Poulin, et al., 1990)

Reproduction

Female Salmincola edwardsii mature slower (11-14 days) than the males of their same generation (3-4 days). Male Salmincola edwardsii have the ability to mate with chalimus IV females of their same generation and with prior generations of unfertilized, adult females. This provides a larger prospect of mating partners and reduces the unfavorable effects of inbreeding. (Conley and Curtis, 1992; Conley and Curtis, 1994; Poulin, et al., 1989; Poulin, et al., 1990)

Behavior

Female Salmincola edwardsii mature slower (11-14 days) than the males of their same generation (3-4 days). Male Salmincola edwardsii have the ability to mate with chalimus IV females of their same generation and with prior generations of unfertilized, adult females. This provides a larger prospect of mating partners and reduces the unfavorable effects of inbreeding.

The first stage of larvae is able to swim and must find the host. It is free-living and non-feeding. It has a brief period of inactivity before it begins to swim. The water temperature also has a significant effect on Salmincola edwardsii's swimming activity and survival. In the best-suited temperatures (cooler) the organism at the infective swimming stage lives much longer. Salmincola edwardsii emerge at sunset when the fish tend to rest near the bottom, and increase their chances of finding a host. Once finding its host it attaches and molts into the chalimus larvae. (Conley and Curtis, 1992; Conley and Curtis, 1994; Poulin, et al., 1989; Poulin, et al., 1990)

Communication and Perception

Crustaceans have various sensory resceptors, mainly setae over the body. Photoreceptors are also generally present.

Food Habits

Salmincola edwardsii is a parasite of a fish in the genus Salvelinus. The most frequently infected Salvelinus in North America is the brook trout, Salvelinus fontinalis. Salmincola edwardsii is commonly found on the body surface, fins, and especially on the gills of its fish host. The intensity of Salmincola edwardsii found in the gills increases with the size of the host. Salmincola edwardsii is attached by a bulla to the distal tips of the host's gill filaments. Only occasionally are they attached to the body of the host. As the host size increases there is more suitable substrate in the gills to which Salmincola edwardsii can attach. (Black, 1982; Black, 1983)

  • Animal Foods
  • blood
  • body fluids

Predation

Although no known predators have been recorded, this species is likely ingested by fish or other aquatic predators. Mortality of the young is likely high.

Ecosystem Roles

Salmincola edwardsii is a parasite of a fish in the genus Salvelinus. The most frequently infected Salvelinus in North America is the brook trout, Salvelinus fontinalis.

Species Used as Host

Economic Importance for Humans: Negative

Salmonid fish, such as trout that are raised in commercial hatcheries are at high risk for heavy infestations of S. edwardsii. Salmincola edwardsii can cause infections and create serious health problems for fish in cage culture. Larger fish circulate more water over their gills and thus bring more S. edwardsii (also other copepodids) in contact with them. Ironically, in natural fish populations the occurrence and intensity of the infection of S. edwardsii are usually low and have little impact of the fish.

The fish is only vulnerable for the period of time when S. edwardsii is in its infective, free-living stage looking for a host. If the timing of egg hatching and the release of the free-living stage can be timed, hatcheries will know when the fish can become infected and hopefully in the future control S. edwardsii infection. In times of high temperatures and low dissolved oxygen, fish with many S. edwardsii attached to their gills have an especially difficult time. Also as a result of high infestation, growth and sexual maturation is stunted. (Amundsen, et al., 1997; Conley and Curtis, 1992; Poulin, et al., 1989)

Other Comments

Salmincola edwardsii is in the group (subclass) Copepoda. The name copepod means literally in Greek "oar-footed." This is a reference to the shape of the swimming legs Copepods have. A French scientist, Henri Milne Edwards, was the first to use the name of Copepod in 1840. He first used this name in his book, Histoire Naturelle des Crustaces. (Strickler, 2000)

Contributors

Renee Sherman Mulcrone (editor).

Megan Harris-Linton (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sessile

non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa

tactile

uses touch to communicate

visual

uses sight to communicate

References

Amundsen, P., R. Kristoffersen, R. Knudsen, A. Klemetsen. 1997. Infection of Salmincola edwardsii (Copepoda: Lernaeopodidae) in an age-structured population of Artic charr-a long term study. Journal of Fish Biology, 51: 1033-1046.

Black, G. 1982. Gills as an attachment site for Salmincola edwardsii (Copepoda: Lernaeopodidae). Journal of Parasitology, 68 (6): 1172-1173.

Black, G. 1983. Abundance and distribution of Salmincola edwardsii on anadromous brook tout, Salvelinus fontinalis in the Moisie River system, Quebec. The Fisheries Society of the British Isles, 22 (5): 567-575.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Conley, D., M. Curtis. 1992. Effects of temperature and photoperiod on the duration of hatching, swimming, and copepodid survival of the parasitic copepod Salmincola edwardsii . Canadian Journal of Zoology, 71 (5): 972-976.

Conley, D., M. Curtis. 1994. Larval development of the parasitic copepod Salmincola edwardsii on brook trout (Salvelinus frontinalis). Canadian Journal of Zoology, 72 (1): 154-159.

Poulin, R., D. Conley, M. Curtis. 1989. Effects of temperature fluctuations and photoperiod on hatching in the parasitic copepod Salmincola edwardsii . Canadian Jounal of Zoology, 68 (6): 1330-1332.

Poulin, R., M. Curtis, M. Rau. 1990. Responses of the fish ectoparasite Salmincola edwardsii (Copepoda) to stimulation, and their implication for host-finding. Parasitology, 100 (3): 417-421.

Roberts, L., J. Janovy, Jr. 2000. Gerald D. Schmidt & Larry S, Roberts' Foundations of Parasitology Sixth Edition. Boston: McGraw-Hill Companies, Inc..

Strickler, J. 2000. "Nerd's Corner" (On-line). Accessed 10/21/04 at http://www.uwm.edu/~jrs/nerd.htm.