Thermal tolerance and preference of some native New Zealand freshwater fish

Upper lethal and preferred temperatures were determined experimentally for eight common species of New Zealand freshwater fish. Upper lethal temperatures ranged between 28.3 and 39.7°C and preferred temperatures between 16.1 and 26.9°C. Anguilla australis was the most tolerant of high temperatures, whereas Retropinna retropinna and two species of Galaxias preferred cooler water. The relationship between lethal and preferred temperatures for New Zealand species was similar to that calculated from data for 38 other species of freshwater fish, meaning that either lethal or preferred temperatures could be used accurately to predict lethal, preferred, and growth optima, and to recommend temperature regimes for waterways. However, New Zealand field records show that significant relationships between fish density and water temperature exist for only two species, A. dieffenbachii and Cheimarrichthys fosteri. This suggests New Zealand species are able to thrive within a wide temperature range.