Although most of the notothenioid fishes have geographic distributions restricted to the Southern Ocean, several species with inferred Antarctic origins have come to permanently inhabit the warmer waters around New Zealand and southern South America. However, it remains unknown whether the Antarctic ancestry of these secondarily temperate species continues to influence their modern heat tolerance. We investigated the heat tolerance of one such secondarily temperate nototheniid, Notothenia angustata, which is now endemic to the waters around the South Island of New Zealand. Their heat tolerance was determined using the critical thermal maximum (CTMax) both when acclimatized to their winter water temperatures (7.9°C), and warm acclimated (15°C) near the summer water temperatures in Otago Harbour. When compared to equivalently acclimated specimens of the basal New Zealand notothenioid Bovichtus variegatus, N. angustata have consistently lower CTMaxs, though they are significantly greater than those determined from 10°C acclimated specimens of its endemic Antarctic congener, N. coriiceps. While this shows greater heat tolerance in the secondarily temperate N. angustata than in endemic Antarctic species, it also suggests that some of its ancestral intolerance to heat persists.
- black cod
- critical thermal maximum