The family Argulidae, whose members are commonly known as carp lice or fish lice, (not to be confused with Caligidae, also commonly referred to as sea lice) are parasitic crustaceans in the class Ichthyostraca. It is the only family in the monotypic subclass Branchiura and the order Arguloida, although a second family, Dipteropeltidae, has been proposed.
Taxonomy
Branchiurans were once thought to be copepods but are now recognised as a separate subclass in the superclass Oligostraca due to their distinct morphological characteristics. There are approximately 170 species in four genera recognised in the family Branchiura. The centres of diversity are the Afrotropical and Neotropical realms.
Description
Branchiurans have a flattened, oval body, which is almost entirely covered by a broad, oval carapace, four thoracic segments each with a pair of swimming legs, a pair of anterior compound eyes, and an unsegmented abdomen without appendages which ends in paired abdominal lobes separated by the medial anal cleft. They are compressed dorsoventrally and can vary in size from just a few millimetres to over long, with females usually somewhat larger than the males.
Distribution and habitat
Branchiurans are widely distributed throughout the world. Most species are found in Africa and South America, and none are found in Antarctica. In North America, the genus Argulus is the only one known to be found in freshwater ecosystems.
Behaviour and ecology
Parasitism
Branchiurans are obligate ectoparasites that are found primarily on marine and freshwater fish (only the genus Argulus occurs in marine environments), but can also be found on other aquatic organisms such as invertebrates, salamanders, tadpoles and alligators. After engorging themselves, the parasites typically wait two to three weeks before feeding again. From this study, it is thought that Tobacco leaf dust (containing nicotine) can safely and effectively eliminate adult Branchiurans from fish, although this may be specific to only Argulus bengalensis. Branchiurans are not permanently attached to their hosts, and leave them for up to three weeks to mate and lay eggs, and reattach behind the fish's operculum, where they feed on mucus and sloughed-off scales, or pierce the skin and feed on the internal fluids. The eggs hatch into parasitic postnauplius larvae. While on their host, Branchiurans mate.
Impact
Fish lice occasionally reach high enough densities to cause fish kills in aquaculture operations, or more rarely in wild populations of fish. They can also become abundant in aquaria, sometimes resulting in the death of ornamental fish.