Means (±SE) of (a) numbers of aggressive behaviours and (b) the duration of male fights in males from two extremophile populations in the Cueva del Azufre system, one from the sulphidic surface stream [El Azufre, EA ()] and one from chamber X of the sulphidic Cueva del Azufre [CA-X ()]. Prior to the tests, males were either fed on a normal diet (left bars) or starved for one week (s: right bars).