Tolerance of headwater vs. mainstream fishes for abrupt physicochemical changes

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