Anna Rocka

Helminths of Antarctic fishes: Life cycle biology, specificity and geographical distribution

Bony fishes (Teleostei) play an important role in the completion of life cycles of helminth parasites in the Antarctica. These fishes may be definitive, second intermediate or paratenic hosts of the helminths. The most species-rich taxon is Digenea. Virtually all of these digeneans use teleosts as definitive hosts. Only one species, Otodistomum cestoides, occurs as the adult stage in skates (Chondrichthyes), with teleosts as its second intermediate host. Among 14 cestode species maturing in fishes only one, Parabothriocephalus johnstoni, occurs in a bony fish, Macrourus whitsoni, whereas the others are parasites of Chondrichthyes (cartilaginous fishes). Antarctic Chondrichthyes are not infected with nematode and acanthocephalan species. Specificity to the intermediate and/or paratenic hosts of the majority of Antarctic helminths is wide, whereas that for definitive hosts is often narrower, restricted to one order or sometimes even to one or two host species. Almost all of 73 helminth species maturing in Antarctic fishes are endemics. Only 4 digenean and one nematode species are cosmopolitan or bipolar.

Molecular identification larvae of Onchobothrium antarcticum (Cestoda: Tetraphyllidea) from marbled rockcod, Notothenia rossii, in Admiralty Bay (King George Island, Antarctica)

Antarctic bony fishes are infected with cestode larvae belonging to the order Tetraphyllidea (parasites as adults in chondrichthyans). Larvae of the Tetraphyllidea differ from each other in the morphology of their scoleces and represent five forms. There are larvae with bothridia subdivided into one, two and three loculi, bothridia sac-like in shape and bothridia undivided with hook-like projections. Only one species of the family Onchobothriidae, Onchobothrium antarcticum, has been described from Antarctica and larvae with trilocular bothridia were assigned to this cestode species. In this study, ten larvae obtained from Notothenia rossii and three adult specimens of Onchobothrium antarcticum isolated from Bathyraja eatonii were examined. A partial sequence of cytochrome c oxidase subunit 1 of three adult specimens and four larvae was identical. The remaining six larval sequences differed from the sequences obtained from adult cestodes. Partial sequences of lsrDNA of all analyzed larvae were identical. These results confirm the taxonomic affiliation of the larvae with trilocular bothridia parasitizing marbled rockcod in Antarctica as Onchobothrium antarcticum.

Cestodes and Nematodes of Antarctic Fishes and Birds

According to Duhamel et al. (2014) fish comprise the most species-rich group of Antarctic vertebrates with 47 families and 374 species; four families of which, including 14 species, being cartilagineous (Chondrichthyes). The most dominant is the endemic family Nototheniidae with 115 species (eight species require validation). Chondrichthyes are represented by sharks (three families, five species) and rays (one family, nine species). Sharks are mainly recorded in the northern part of the Southern Ocean, with only one southerly record in the Ross Sea. All Antarctic skates belong to the family Rajidae and two genera: Amblyraja Malm, 1877 (two species) and Bathyraja Ishiyama, 1958 (seven species).