Species identification based on the morphometry of opisthaptoral hard parts, in combination with internal transcribed spacer ribosomal DNA (ITS rDNA) region sequences, confirmed the presence of four viviparous Gyrodactylus von Nordman, 1832 (Plathyhelminthes, Monogenea) species on Nototheniid fish from the Prince Gustav Channel (Weddell Sea, Antarctica). Gyrodactylus antarcticus Gusev, 1967 was found mostly on Trematomus newnesi Boulenger (93 specimens) but also on T. bernacchii Boulenger (one specimen), the latter representing a new host record for this species. Gyrodactylus byrdi Hargis & Dillon, 1968 and G. coriicepsi Rokicka, Lumme & Ziętara, 2009 were recorded on their type hosts, T. newnesi and Notothenia coriiceps Richardson, respectively. Gyrodactylus wilkesi Hargis & Dillon, 1968 was found mostly on the fins of T. bernacchii (29 specimens), but also on T. hansoni Boulenger (one specimen) and T. newnesi (three specimens). The finding of G. wilkesi on T. newnesi represents a new host record. The low number of Gyrodactylus specimens may indicate an accidental infection. The occurence of all four Gyrodactylus species in the Prince Gustav Channel represents a new locality record. According to phylogentic methods, the newly redescribed monogeneans belong to the Antarctic lineage, forming a sister group to North American and European marine Gyrodactylus species, and consist of two species groups, one comprising G. coriicepsi and G. nudifronsi Rokicka, Lumme & Ziętara, 2009, and the other G. anarcticus and G. wilkesi.

In this study, we analysed and compared the whole parasite community from the fish Notothenia rossii and Notothenia coriiceps collected from Fildes Bay at King George Island, Antarctica, during January–February 2017 in a field campaign supported by the Chilean Antarctic Institute. The fish samples collected were 45 specimens of N. rossii and 22 of N. coriiceps, with total lengths averaging 29.7 ± 5.3 cm and 32.5 ± 3.2 cm, respectively. Fish were dissected to collect their internal and external parasites. All the fish were parasitized; 13 taxa were found in N. rossii and 12 taxa in N. coriiceps. Acanthocephalans, mainly Metacanthocephalus johnstoni and Aspersentis megarhynchus, were the most abundant and prevalent parasites in both fish species. The abundance and richness of the parasite infracommunity increased with the host body length only in N. rossii. Twelve parasitic taxa were shared by both notothen species. Abundance and prevalence of parasitic taxa, as well as the average richness and abundance of the parasite infracommunities were mostly similar between the two fish species. Parasite compositions of N. coriiceps reported in published studies from King George Island were relatively comparable to our sample. We concluded that the two congeneric and sympatric fish species had highly similar parasite communities, which indicates that they use resources in a similar way, thus allowing them to become parasitized with the same parasitic species and in the same abundances. All parasites recorded in this study have been found in several other fish species; therefore, parasites from notothens are considered to be generalists.

The diet of post-breeding Antarctic shags Phalacrocorax bransfieldensis was investigated at four colonies at the Danco Coast, Antarctic Peninsula, by the analysis of 399 pellets (regurgitated casts) collected during February and March 1998 and 2000. Overall, demersal-benthic fish were the most frequent and important prey at all the colonies sampled, followed by octopods and gastropods. Amongst the fish, Notothenia coriiceps and Gobionotothen gibberifrons were the main prey in all of the sampling sites in both seasons. The composition of the diet of post-breeding shags differed from that observed in the previous breeding season. Post-breeders preyed on the same fish species consumed by breeders, although in different proportions and on larger specimens. The information provided here differs from that reported for post-breeding individuals belonging to other shag species and also for post-breeding Antarctic shags. Our results, as well as the differences with previous studies, are discussed in relation to differences in prey availability among localities and to the use of alternative foraging grounds at the end of the breeding period.

A sample of 111 fish of eight species caught in two fjords at South Georgia were examined for digenean trematode parasites. The alimentary tracts of all specimens were infected with digeneans. The dominant species was Elytrophalloides oatesi (Leiper & Atkinson) which was found in all fish, with a maximum number of 1961 specimens per fish. Other common species were; Macvicaria pennelli (Leiper & Atkinson), Lepidapedon garrardi (Leiper & Atkinson), Lecithaster macrocotyle Szidat & Graefe, Genolinea bowersi (Leiper & Atkinson) and Postmonorchis variabilis Prudhoe & Bray. Three further species, Neolebouria antarctica (Szidat & Graefe), Discoverytrema markowskii Gibson and Gonocerca phycidis Manter, were rare. Infection of the most commonly caught fish at South Georgia, Notothenia rossii Richardson, is compared with that of N. rossii at Admiralty Bay, South Shetland Islands. The species composition of common parasites was similar in both areas but conspicuous differences in the frequency of individual digenean species were found.