Ergasilidae
Encyclopedia
Ergasilidae is a widespread family of copepod
s and comprises many species. The type genus is Ergasilus. With a few doubtful exceptions all ergasilids are parasitic
on fish
es.
in various habitats
, mostly freshwater, but some attack marine species, especially euryhaline
fishes such as mullet. Because the best-known species are adapted to attack the gill
filaments of the fishes, Ergasilidae are known by common names such as gill lice. However, some species have been found infesting, and presumably causing, external skin lesions of fish.
Immature instar
s and mature males of Ergasilidae are fairly typical free-living plankton
ic copepods. The mature females also can swim competently and at least one species, Ergasilus chautauquaensis, is not known to be parasitic at all. However, that is exceptional; most adult females are parasitic and have morphological
adaptations for attacking the gills of host species of fishes.
Though their antennules
retain their sensory
function, the main second antennae of the adult females are adapted to clinging to the gill
filaments of host fishes. In many Ergasilus species it is not clear that mature females are able to release their grip once attached, but when forcibly detached from the host's gills they swim without difficulty.
Another adaptation in parasitic females is that their first legs are armed with heavy, blade-like spines, and in some species the joints also are fused, stiffening them and increasing their effectiveness for harvesting host tissue
. Once attached to the gills, the females use their first pair of legs to rasp off gill mucus
and tissue and move it forward towards the mouth.
In the genus Ergasilus only the adult females are parasitic. The planktonic males do not venture inside fishes, so fertilisation must take place before the females attach themselves to the host's gills.
and morbidity
among fish stocks can present serious economic and ecological problems.
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s and comprises many species. The type genus is Ergasilus. With a few doubtful exceptions all ergasilids are parasitic
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
on fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es.
Biology
Various species of Ergasilidae parasitise hostsHost (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
in various habitats
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
, mostly freshwater, but some attack marine species, especially euryhaline
Euryhaline
Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly which can live in fresh, brackish, or salt water. The European shore crab is an example of a euryhaline invertebrate that can live in salt and brackish water...
fishes such as mullet. Because the best-known species are adapted to attack the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
filaments of the fishes, Ergasilidae are known by common names such as gill lice. However, some species have been found infesting, and presumably causing, external skin lesions of fish.
Immature instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
s and mature males of Ergasilidae are fairly typical free-living plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic copepods. The mature females also can swim competently and at least one species, Ergasilus chautauquaensis, is not known to be parasitic at all. However, that is exceptional; most adult females are parasitic and have morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
adaptations for attacking the gills of host species of fishes.
Though their antennules
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
retain their sensory
Sensory receptor
In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism...
function, the main second antennae of the adult females are adapted to clinging to the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
filaments of host fishes. In many Ergasilus species it is not clear that mature females are able to release their grip once attached, but when forcibly detached from the host's gills they swim without difficulty.
Another adaptation in parasitic females is that their first legs are armed with heavy, blade-like spines, and in some species the joints also are fused, stiffening them and increasing their effectiveness for harvesting host tissue
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
. Once attached to the gills, the females use their first pair of legs to rasp off gill mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
and tissue and move it forward towards the mouth.
In the genus Ergasilus only the adult females are parasitic. The planktonic males do not venture inside fishes, so fertilisation must take place before the females attach themselves to the host's gills.
Economic significance
Since the Ergasilus females attack the gills of fish, a heavy infestation can cause severe damage and secondary infections, interfere with respiration, and sometimes kill the host. In some fisheries and aquacultural enterprises the mortalityMortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
and morbidity
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
among fish stocks can present serious economic and ecological problems.
Genera
The family Ergasilidae contains the following genera:- AbergasilusAbergasilusAbergasilus amplexus is a species of parasitic copepod endemic to euryhaline habitats in New Zealand. It is currently the only known species in the genus Abergasilus.-Description:...
Hewitt, 1978 - Acusicola Cressey, 1970
- Amplexibranchius Thatcher & Paredes, 1985
- Anklobrachius Thatcher, 1999
- Brasergasilus Thatcher & Boeger, 1983
- Dermoergasilus Ho & Do, 1982
- Ergasilus von Nordmann, 1832
- Gamidactylus Thatcher & Boeger, 1984
- Gamispatulus Thatcher & Boeger, 1984
- Gamispinus Thatcher & Boeger, 1984
- Gauchergasilus Montu & Boxshall, 2002
- Majalincola Tang & Kalman, 2008
- Miracetyma Malta, 1993
- Mugilicola Tripathi, 1960
- Neoergasilus Yin, 1956
- Nipergasilus Yamaguti, 1939
- Paeonodes C. B. Wilson, 1944
- Paraergasilus Markevich, 1937
- Pindapixara Malta, 1994
- Prehendorastrus Boeger & Thatcher, 1990
- Pseudovaigamus Amado, Ho & Rocha, 1995
- Rhinergasilus Boeger & Thatcher, 1988
- Sinergasilus Yin, 1949
- Teredophilus Rancurel, 1954
- Therodamas Krøyer, 1863
- Thersitina Norman, 1905
- Vaigamus Thatcher & Robertson, 1984