| Argulidae | |
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| Argulus sp. on astickleback | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Ichthyostraca |
| Subclass: | Branchiura Thorell, 1864 |
| Order: | Arguloida Yamaguti, 1963 |
| Family: | Argulidae Leach, 1819 |
| Genera | |
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ThefamilyArgulidae, whose members are commonly known ascarp lice orfish lice, areparasiticcrustaceans in the class Ichthyostraca. It is the only family in themonotypic subclassBranchiura and the orderArguloida, although a second family, Dipteropeltidae, has been proposed.[1][2]
Branchiurans were once thought to becopepods but are now recognised as a separate subclass in the superclassOligostraca due to their distinct morphological characteristics.[3] There are approximately 170 species in four genera recognised in the family Branchiura.[4] Thecentres of diversity are theAfrotropical andNeotropicalrealms.[5]
Branchiurans have a flattened,oval body, which is almost entirely covered by a broad, ovalcarapace, 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.[6][7][8] They are compressed dorsoventrally and can vary in size from just a few millimetres to over 30 mm (1.2 in) long, with females usually somewhat larger than the males.[5]
The mandibles are generally toothed hooks in Branchiurans. The maxillules provide sucking capability, and in the generaArgulus, Chonopeltis, andDipteropeltis, the adults have a pair of suction cups that are from modified first maxillae.[6] The genusDolops, keeps the larval stages claw-like appendages into adulthood.[6] It is still unknown whether the ancestral state of these organisms had suction discs or the hooked condition seen inDolops, although it is thought that the specialized suctions discs are a later product of evolution.[9] Also, females tend to be larger than the males.[6] Between the genera there are multiple distinction between the sexes.[6] For example, males inArgulus andChonopeltis possess secondary sexual modifications on legs 2–4.[6] The sexes both have their own sexual reproductive organs on their abdomens.[6] The females have a spermathecae, while the males have a pair of testes.[6]
Theircompound eyes are prominent, and themouthparts and the first pair ofantennae are modified to form a hooked, spinyproboscis armed with suckers, as an adaptation to parasitic life. They have four pairs ofthoracicappendages, which are used to swim when not attached to the host.[5]
Not much research has been done on the respiratory system, which lacks gills, but respiratory areas on the carapace and gas exchange through the fleshy abdomen has been suggested.[10][11]
Branchiurans are widely distributed throughout the world. Most species are found in Africa and South America, and none are found in Antarctica.[12] In North America, the genusArgulus is the only one known to be found in freshwater ecosystems.
Branchiurans areobligate ectoparasites that are found primarily on marine and freshwater fish (only the genus Argulus occurs in marine environments),[13] but can also be found on other aquatic organisms such as invertebrates, salamanders, tadpoles and alligators.[6][14][3] Some species feed on the blood of their host, while others feed on mucus and extracellular material.[3] Feeding is facilitated by distinct morphological adaptations (see Anatomy). Branchiura are able to attach to hosts through two mechanisms, hooked maxillae (as seen inDolops) or suction disks.[9] After engorging themselves, the parasites typically wait two to three weeks before feeding again.[3] Mitigation of these parasites has been studied through the use of a treatment containing plant parts.[15] 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 onlyArgulus bengalensis.[15]
Only the life cycle of freshwater forms of the genusArgulus is well known.[16] 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'soperculum, where they feed onmucus and sloughed-offscales, or pierce the skin and feed on the internal fluids.[17] The eggs hatch into parasiticpostnauplius larvae. While on their host, Branchiurans mate.[6] The female holds the eggs in the thorax and in some species the eggs can be found inside the lobes of the carapace.[6] The spermathecae on the female stores the sperm.[6] In the genusDolops, the males deposit a spermatophore onto the females.[6] Once the eggs are fertilized the females leave the host organism to lay their eggs in rows on surfaces of plants, rocks, etc.[6] Like the adults, the larvae are parasites on fish. They are opportunistic in selecting host species of fish, and females are motile in their pursuit of locality of egg-laying.Chonopeltis larvae appear to be less developed than those of the other genera. Members of one group ofArgulus hatch as metanauplius-larvae, followed by a juvenile stage. AnotherArgulus group, and all known species ofDolops, hatch as juveniles.[18]
Fish lice occasionally reach high enough densities to causefish kills inaquaculture operations, or more rarely in wild populations of fish. They can also become abundant inaquaria, sometimes resulting in the death ofornamental fish.[5]
Authority control databases: National |
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