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.

A study of feeding selectivity in Notothenia neglecta Nybelin 1951, was carried out between October 1988 and January 1989 at Potter Cove, King George Island, where this is the dominant fish species. The abundance and biomass of benthic organisms from 0–40m were compared with their occurrence in the diet of 142 fish. The Ivlev index indicated that the food items positively selected by the fish were sedentary polychaetes, the isopod Glyptonotus antarcticus, the gammarid amphipod Paradexamine sp., the bivalve Dacrydyum sp., the gastropods Margarella antarctica and Eatoniella sp., and algae. The biomass of the benthic community in the sampling area was low, presumably due to the effects of anchor ice. Despite being pelagic, krill (Euphausia superba) was by far the main food of N. neglecta which is considered a benthic feeder.

A histochemical and electron microscopy study was carried out on muscle growth in demersal stages of the Antarctic teleost Notothenia neglecta Nybelin. The total number of myotomal muscle fibres was similar in fish ranging in body mass from 11.9g to 889g. Post-anal myotomes contained around 17,000 slow muscle fibres and 70,000 fast muscle fibres. Myosatellite cells were extremely rare. The diameter of fast fibres varied from <10μm to 130μm in the smallest, and from >40μm to 450μm in the largest fish studied. Slow muscle fibre diameters in the largest fish ranged from >30μm to 260μm. Even the largest diameter slow fibres contained significant numbers of mitochondria, which suggests that the diffusion of oxygen does not limit metabolism. The results confirm that muscle fibre hyperplasia ceases prior to the demersal stages of the life history, and that subsequent muscle growth is entirely via the hypertrophy of existing fibres. Comparative studies suggest that this may be one of the factors contributing to the relatively slow rate of somatic growth in this species.

Scales and whole otoliths were used for age estimation of juvenile Notothenia rossii specimens collected at Potter Cove, King George Island, South Shetland Islands, between 1983 and 1988. Results from the analysis of both types of material showed 96.7% agreement. Likewise, the examination of otolith cross sections of chosen specimens confirmed in all the cases the age readings obtained from the second whole sagittal otolith. Although the commonly accepted 1 July was used as the birth date of the fish for age calculations, data indicate that 1 October is closer to the biological birth date, since this species hatches in Spring. The length-age range of the fish was 18–44 cm and 3–7 years respectively, which fits well with the known length-age distribution of juvenile specimens of the species in the fjord. A comparison between observed and back-calculated mean length of age group 3 (24.6 and 25 cm respectively) indicated that not only the larger fish but the full size range of this age group was represented in our samples. Mean length data at age presented here are similar to the ones reported for fish from Admiralty Bay, King George Island, but differ from those of fish caught off Elephant Island. The use of whole otoliths for age estimation of juvenile N. rossii proved to be a reliable method with a precision of one year but, this might not be an appropriate technique for adult specimens.

Chlorinated hydrocarbons were measured in seven species of Antarctic fish (Pagothenia bernacchii, P. hansoni, Trematomus centronotus, T. newnesi, Chionodraco hamatus, Cygnodraco mawsoni, and Gymnodraco acuticeps) from in the Ross Sea near Terra Nova Bay (74°40'S 164°10'E). Hexachlorobenzene (HCB), pp' DDT and its derivatives DDE and DDD, and about 20 congeners of polychlorinated biphenyls (PCBs)were found in muscle and liver. Levels of pp′ DDE were positively correlated with body length in P. bernacchii and the plot of concentrations showed higher values in males than females of the same body weight class. The results confirm the presence of these chlorinated hydrocarbons in the Antarctic marine food chain and an increase of PCBs with respect to DDTs. The “fingerprint” of C. hamatus is different from that of other Antarctic organisms and of fish from other parts of the world, suggesting possible metabolic differences.

In Potter Cove, King George Island, Antarctica, macroalgae provide a significant food resource for herbivores. The demersal fish Notothenia coriiceps feeds on macroalgae. Eighteen algal species were identified in stomach contents: two chlorophytes, ten rhodophytes and six phaeophytes. Among these the rhodophyte Palmaria decipiens, the phaeophyte Desmarestia menziesii and the chlorophyte Monostroma hariotii comprised the greatest proportions of algal biomass. A food selection study showed four algae to be preferred (P. decipiens, M. hariotii, D. menziesii, Iridaea cordata) and two species to be avoided (Desmarestia anceps and Himantothallus grandifolius) by N. coriiceps. The present investigation indicates that this fish feeds not only intentionally, but also selectively, on macroalgae. Preference for particular algal species is not related to associated epifaunal biomass or to associated amphipod biomass.

The majority of species of the Antarctic coastal fish fauna is represented today by the perciform suborder Notothenioidei. The separation of basal lineages of notothenioids has been estimated to have occurred between 23 and 22 million years ago (m.y.a.), while a major diversification probably occurred 16–10 m.y.a. Cytogenetic approaches aim to study the genomic change that, at the cell level, accompanied the radiation of this group. The information available for 66 of 120–130 species makes possible the description of the main patterns of chromosome diversification within the suborder. Within some families (Channichthyidae, Artedidraconidae) the range of the chromosomal variability seems to be minimal whilst the high karyotypic diversity of Nototheniidae and Bathydraconidae is consistent with morphological and molecular data suggesting the paraphyletic nature of these two taxa. Molecular cytogenetics allows detailed chromosome characterization, including mapping of ribosomal genes and of telomeric sequences, thus providing information on processes of karyotypic rearrangement and direction of chromosomal change. Active process of genomic restructuring leads to intraspecific variability in several species, at different levels of chromosomal organization. The growing amount of information make it possible to use notothenioids as a model for testing hypotheses of evolutionary change in marine organisms, including chromosomal diversification.

The jaw musculature of notothenioid fishes is described and compared based on a total of 38 species referred to eight families of the suborder Notothenioidei. In the Notothenioidei, the adductor mandibulae, the largest and most conspicuous of the cranial muscles, is generally composed of sections A1, A2, A3 and Aw as in the generalized percoids. The morphology of the adductor mandibulae is similar in most notothenioid families except the Nototheniidae and Bathydraconidae. Notothenia, Paranotothenia and Dissostichus are clearly distinguished from the other nototheniid genera in having A3. Gymnodraco of the Bathydraconidae has a fused A1-A2 complex and the anterior element is segmented by a tendinous intersection from the A1-A2 complex. These features are unique to Gymnodraco and not seen in other bathydraconids. The Harpagiferidae and Artedidraconidae share the same apomorphy, the presence of A1β, with the Nototheniidae and have no synapomorphies with the Bathydraconidae and Channichthyidae. The character distribution, however, shows some inconsistencies with the previous classifications. Based on the limited evidence obtained in this study, the Notothenioidei can be divided into six groups and it seems reasonable to suggest a review of the current classification of the Nototheniidae.