Thermal Tolerance and Growth Differences in Orangethroat Darter (Etheostoma spectabile) from Thermally Contrasting Adjoining Streams

Orangethroat darters Etheostoma spectabile occupying thermally contrasting streams within the same watershed were tested for differences in thermal responses by comparing their critical thermal maxima (CTM) and short-term growth. Individuals from a spring branch population had a lower CTM, better growth at low temperatures and more inhibited growth at higher temperatures compared to individuals collected from a thermally variable adjoining stream reach. The findings support the contention that intraspecific differences in thermal tolerance and growth may exist at relatively localized scales within a small watershed.