Cestodes of Antarctic and Subantarctic fish: History and prospects of research

The first information about cestodes of Antarctic and Subantarctic fish appeared at the beginning of the XX century: a cestode Phyllobothrium dentatum from an unknown shark was described. Peak of activity of studying Antarctic cestodes fell on 1990–2006. During this period, significant works were published, devoted to description of new species, their life cycles, host specificity of cestodes – fish parasites, and their geographical distribution. A notable contribution to the study of elasmobranch cestodes was made by a group of Polish scientists, headed by Wojciechowska (Rocka). Systematic position of 21 cestode species from 13 genera of 8 families of 6 orders was analyzed. Cestode fauna has been studied in less than 7 % of the total ichthyofauna of this area, while potential definitive and intermediate hosts remain unexplored. The largest number of cestode species (12) was recorded in four ray species of the family Rajidae. Eight cestode species, reaching sexual maturity, have been registered in intestines of teleosts: Bothriocephalus antarcticus, B. kerguelensis, Bothriocephalus sp., Parabothriocephalus johnstoni, P. macruri, Clestobothrium crassiceps, Neobothriocephalus sp., and Eubothrium sp. Larvae of five cestode species (Onchobothrium antarcticum, Grillotia (Grillotia) erinaceus, Lacistorhynchus tenuis, Calyptrobothrium sp., and Hepatoxylon trichiuri), ending their development in elasmobranchs, were found in teleosts. Systematic position of 5 cestode species out of 12, found in rays, is unidentified. Cestode fauna is characterized by a high level of endemism: 67 % of the total cestode fauna is not found to the north of Subantarctic. Coastal areas, mostly covered by research, are those in the Atlantic and Indian sectors of Antarctic. The biodiversity of elasmobranch cestodes, inhabiting Antarctic and Subantarctic, is underestimated, since only one third of species of these fish have been studied so far. Genetic studies of Antarctic cestodes have just begun to develop. Ribosomal sequences from D1–D3 segments of 28S rDNA are known only for 2 species: Onchobothrium antarcticum from the second intermediate (Notothenia rossii and Dissostichus mawsoni) and definitive hosts (Bathyraja eatonii), as well as larvae of Calyptrobothrium sp. from the second intermediate hosts (D. mawsoni and Muraenolepis marmorata). The main directions of further research on cestode fauna should be developed in combination with morphological, faunistic, genetic, and ecological studies.