Anyone who has kept and bred any of the Nothobranchius species is well aware of the vivid colors and the energetic courting displays of the males. But just how do fish select their mates, and what factors influence such decisions?
“In general,” says Brian Watters, “Notho females initiate spawning.” This is consistent with observations in the wild that in many cases the males and the females occupy different parts of the habitat, suggesting that one gender must seek out the other in order to mate. Experiments by Dr. Richard Hass with N. guentheri indicated that females chose the males and initiated spawning, and also that they had a distinct preference for the color red, perhaps to aid in the identification of males in turbid water. Studying N. jubbi (his N. neumanni), he found that females preferred red-tailed males even when many males from their own population did not have them. This preference may be balanced by the greater predation suffered by the red-tailed males.
However, Brian adds, “I do not believe that it is as simple as that.” When multiple species of Nothos co-exist in a habitat, there are always clearly visible differences between the females of different species. This suggests that it is also necessary that the males identify the correct females; mate recognition apparently works both ways to some degree. In areas where males of different species are similarly colored (such as N. guentheri and N. melanospilus, both of which sport red caudals) the females have distinguishing characteristics; female N. melanospilus females have spots; female N. guentheri do not. In species without male red caudals, pattern recognition rather than the actual color seems to be the key factor.
There may also be species specific behaviors and reactions to indicate a female’s readiness to spawn; and a male’s willingness to mate with her. These behaviors may have little or no effect on individuals of other species, but to those of their own species clearly signal readiness to fight or to mate.
This phenomenon of sharper signals being involved in mate selection when two closely related species occur together has long been noted by biologists. Some interesting results have been achieved from various studies of the phenomenon.
Working with natural guppy populations in Trinidad, John Endler found that red color patterns in fish were due to carotenoid pigments, which fish do not manufacture. The more food (other animals containing the carotenoid pigments) eaten, the fitter and more brightly colored the fish, thus potentially the better mate. Some of the red and orange colors in Nothos may be similarly acquired. This ties in with the “super fit” theory espoused by some, namely “I’m this big and this colorful” so I must be the best possible mate you can find.
Sexual selection is an aspect of killikeeping whose details have yet to be worked out for most species. However, it appears to involved with inherited male and female colors, and inherited preferences. Those individuals who readily recognize species recognition markings enjoy more reproductive success, thus perpetuating the species and their own selection criteria. – G.C.K.A. Newsletter, November 1998