Tolerance of Headwater vs. Mainstream Fishes for Abrupt Physicochemical Changes

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Abstract
A headwater cyprinid (Phoxinus oreas) of the Roanoke River drainage (Virginia [USA]) was compared to 3 mainstream cyprinids (Notropis ardens, N. albeolus and N. cerasinus) for tolerance of abrupt changes in dissolved O2, temperature and pH. A darter common in the headwaters (Etheostoma flabellare) was compared to 2 mainstream darters (E. podostemone and Percina roanoka) for tolerance of low O2. In all interspecific comparisons, species characteristic of intermittent headwaters were more tolerant than those restricted to the more environmentally stable mainstream. E. flabellare from intermittent headwaters were more tolerant of low O2 conditions than conspecifics from the river mainstream.