Effects of a gradual increase in temperature on the antioxidant defense system and plasma metabolic parameters in Antarctic fish Notothenia rossii

Antarctica is considered a thermally stable ecosystem; however, climate studies point to increases in air and surface water temperatures in this region. These thermal changes may affect the biological processes of animals inhabiting such regions because they are stress factors and may promote metabolic changes, rendering the animals more vulnerable to oxidative damage. Plasma parameters are also good indicators of stress and allow analysis of the metabolic status of fish under temperature increases. The present study assessed the effect of acclimation temperature on the levels of plasma, osmoregulatory and oxidative metabolism parameters and antioxidant defenses in kidney, gill, liver and brain tissues of Notothenia rossii subjected to gradual temperature changes of 0.5°C/day until reaching temperatures of 2, 4, 6 and 8°C. Under the effect of the 0.5°C/day acclimation rate, gill tissue showed increased glutathione-S-transferase (GST) activity, and kidney tissue showed increased H⁺-ATPase at 9 days of the experiment (2°C). In the liver, consistent increases in the MDA concentration as an indicator of lipid peroxidation (9 (2°C),13 (4°C),17 (6°C) and 21 (6°C) days) were noted, as well as an increase in GSH at 9 days (2°C). In plasma, gradual decreases in the concentrations of total proteins and globulins were observed. These responses indicate the presence of thermal plasticity and an attempt at regulation to mitigate thermal stress. The changes showed that a gradual increase in temperature may cause opposite responses to the thermal shock model in N. rossii.

Comparison of the parasite community of two notothens, Notothenia rossii and N. coriiceps (Pisces: Nototheniidae), from King George Island, Antarctica

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.