Argulus
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Argulus is a genus of crustacean ectoparasites that are commonly known as fish lice. They belong to the subphylum Crustacea and subclass Branchiura. A. foliaceus is one of the most common species and parasitizes a wide range of freshwater fish hosts. The life cycle involves eggs being laid on surfaces in or out of water and hatching into a free-living larval stage called a metanauplius that then attaches to a fish host. It will molt several times on the host until reaching the adult stage, completing its life cycle in around 4-6 weeks. Adults can cause stress, disease transmission, and mortality in fish if
Argulus
- 2. Taxonomic Classification Phylum : Arthropoda Sub-phylum : Crustacea Class : Maxillopoda Sub-class : Branchiura Order : Arguloida Family : Argulidae Genus : Argulus
- 3. Introduction § The species belong to Branchiura (meaning - Gill tails) of crustaceans § It is also called fish lice or common fish louse (but not acctually) § The group of crustacean ectoparasite in the world. § It has very § It causes the disease called argulosis in most of fishes (mostly freshwater ones)
- 4. § Although the infections are , epizootic outbreaks of this can cause very high losses in the commercial aquaculture farms § Cause significant morbidity and mortality when heavily infested fishes § Among other 150 species of brachiurian crustaceans Argulus sp., is encountered as most important genus § Argulids have been reported since 17th century in and § They are very common on goldfish and koi and other freshwater fishes
- 5. § They are in well maintained aquarium, but are introduced along with the fishes from pond or wild caught. § Some of them are also reported in , especially in cage culture systems. § Argulus will helps in transfer host for other fish pathogens like Ø Rhabdovirus carpio (causes Spring viremia of carps) Ø Larval nematodes (intermediate host) Ø Fungus Saprolegnia Ø Some bacteria
- 6. Host range Most of them are freshwater parasites, while a few are found in estuarine or marine environments Some important species are : 1. Argulus foliaceus - Include wide range of hosts of Cyprinidae, Salmonidae, Gobiidae, Gasterosteidae, Acipenseridae, frogs and toads 2. A. japonicus - Goldfish, Cyprinus sp., Ictalurus sp., etc. 3. A. coregoni - Salmonids, Cyprinids and other hosts. 4. A. alosae (Estuarine environment): Cultured salmon (S. salar), and Trout (O. mykiss) 5. Dolops spp. - Oreochromis and Clarias species
- 7. A. foliaceus A. alosae A. coregoni A. japonicus Dolops sp.
- 8. Morphology
- 10. § The mature ones measure about 0.5 to 1.0 cm in length § Body is dorsoventrally flattenned § The body of adults are divided into head, thorax and abdomen. § Head is covered by a broadly and horse-shoe shaped carapace. § Four pairs of modified for swimming
- 11. § Sucker-like first maxillae, these are mobile structures on a . § These are detachable from the fish and used for . § There are compound eyes are important for host detection § Respiratory areas are on the either sides of the carapace, where the and this lies
- 12. § The stylet in argulids lies anterior to the mouth tube and is separate from the digestive tract § Stylet is a , consisting of a long tapering hollow spine and a broad sheath into which the . § Near the tip of the stylet are two openings, one of which may be secretory and the other sensory
- 13. § The proboscis is formed from the bases of the mandibles and the interlocked labrum and labium. § The surface of the labrum and the surface of the labium is covered in . § At the entrance to the mouth are two conical projections, the ‘labial spines’ or ‘siphons’, which have a at the tip.
- 14. § They probably that aid digestion § Proboscis has two large serrate mandibles in it. § These can be everted through the mouth and presumably . § Three guard the opening of the oesophagus, they are finely serrated and act as a filter fine enough to exclude whole cells
- 15. § Sexes are seperate, usually females grow larger than males. § They can usually be recognized well before they are mature by the prominent seminal receptacles (spermathecae) on the abdomen § The basal segments of the of the male are modified for clasping the female. Sexual Dimorphism
- 17. Copulation § During copulation the male attaches to the dorsal side of the female and clasps her § The is twisted under that of the female first to one side and then to the other. § In this way the is brought into direct contact with the of the female. § The spermathecal spine of the female is apparently inserted into the genital atrium of the male and pierces the wall of the ejaculatory duct. § Sperm are then pumped from the ejaculatory duct into the spermatheca
- 18. Life Cycle
- 19. Life Cycle § Argulus has a direct life cycle using only fish as the host § The entire life cycle takes 55 days at 20°C § Adult argulids can survive for several days away from fish. § Females generally lay 300-400 eggs on an suitable surface in that are attached by § Eggs are ovoid and measure about 0.2mm x 0.3mm § After laying the eggs they and .
- 20. Hatching of eggs : § Eggs of hatch in 17 days at 23°C and 30 days at 20°C. § Eggs of hatch after 10 days at 35°C and after 61 days at 15°C. § Eggs of hatch in 35–37 days at 15–16°C § Hatching is asynchronous and unrelated to the position of the egg in the egg mass, or some species, the periphery of the egg mass hatch sooner than those in the centre. The larva of the fish louse has two main stages 1. Metanauplius stage 2. Juvenile stage
- 22. § The hatchlings are copepodid-like, with l § The metanauplius stage are immediately parasitic, usually attaches to the host species on which it will mature. § Metanauplius - It has too well developed swimming apparatus that it cannot be called as the nauplius at all. § These attaches the host with hooked antennae § After several days they moult to the second stage (called Juveniles), which without suckers
- 23. § After a further at intervals of they mature in about 4 weeks, depending on the temperature. § Adults are parasitic on the body or fins of other cyprinids
- 24. References § Book - Fish Diseases and Disorders, Volume 1: Protozoan and Metazoan Infections Second Edition - by P.T.K. Woo § Book - FISH DISEASE- Diagnosis and Treatment Second Edition - by EDWARD J. NOGA § A review of Argulus spp. occurring inUK freshwaters Science Report SC990019/SR1