In other cases, however, infection can lead to small bowel obstruction, which may require surgery, although treatment with albendazole alone (avoiding surgery) has been reported to be successful. Intestinal perforation (an emergency) is also possible. Occurrence
Larval anisakids are common parasites of marine and anadromous fish (e.g. salmon, sardine), and can also be found in squid and cuttlefish. In contrast, they are absent from fish in waters of low salinity, due to the physiological requirements of krill, which are involved in the completion of the worms life cycle. Anisakids are also uncommon in areas where cetaceans are rare, such as the southern North Sea. Due to having complex life cycles, species specific relationships and their eggs being released in the feces of their definitive host, the identification of anisakids in local fish populations can be a useful tool in assessing the range or migratory patterns of their definitive host.Unusual hosts of Anisakis larvae in the Southern Hemisphere, rarely reported, include seabirds, sharks, or sea kraits. Taxonomy
There are currently 13 species known to exist in this genus, with 12 formally described and one additional species given a temporary name (A. simplex sensu Davey, 1971 is a temporary name). There are three additional species classified as taxon inquirendum (A. dussumierii (Brenden, 1870), A. insignis (Diesing, 1851), and A. salaris (Gmelin, 1790) Yamaguti, 1935). There is one another species classified as nomen dubium (A. diomedeae (Linstow)). An additional 17 species names are now currently considered synonyms for the 13 species believed to exist in this genus.
The nematode excysts in the intestine, feeds, grows, mates, and releases eggs into the seawater in the hosts feces. As the gut of a marine mammal is functionally very similar to that of a human, Anisakis species are able to infect humans who eat raw or undercooked fish. Reproduction
Sexual reproduction occurs once the larvae have reached a definitive host and completed their final molt, at which point sexual organs are developed. Females are capable of producing 2.6 million eggs, depending on species and size at sexual maturity.The known diversity of the genus has increased greatly since mid-1980s with the advent of modern genetic techniques in species identification. Each final host species was discovered to have its own biochemically and genetically identifiable "sibling species" of Anisakis, which is reproductively isolated. This finding has allowed the proportion of different sibling species in a fish to be used as an indicator of population identity in fish stocks. Morphology
Anisakis share the common features of all nematodes: the vermiform body plan, round in cross section, and a lack of segmentation. The body cavity is reduced to a narrow pseudocoel. The mouth is located anteriorly and surrounded by projections used in feeding and sensation, with the anus slightly offset from the posterior. The squamous epithelium secretes a layered cuticle to protect the body from digestive acids. As with all parasites with a complex life cycle involving a number of hosts, details of the morphology vary depending on the host and life cycle stage.