Response of Betta splendens to Computer Animations of Males with Fins of Different Length

The fins of many fish species are modified for functions that have little to do with swimming ability. In fact, the elaborate changes in fin size and shape shown in species such as the guppy, Poecilia reticulata and the Siamese fighting fish, Betta splendens, would appear to be detrimental to optimal swimming performance. Two hypothesis have been proposed to explain the evolution of these sexually dimorphic, elaborate characters. The first hypothesis is that females prefer males with larger fins (Bischoff et al., 1985; Farr, 1989; Basolo, 1990). The second hypothesis contends that larger fins play a role in male-male competition (see Farr, 1989; KodricBrown, 1990). The preceding studies not withstanding, very little is known about the function of elaborate fins in fishes.