Polymorphism and pair formation in the mosquitofish Gambusia holbrooki (Pisces: Poeciliidae)

Synopsis Pair formation was studied in a polymorphic population of Gambusia holbrooki in a brackish drainage canal in Southern Florida. All females and the majority of males were gray colored and only 5% of the males were black spotted. A small fraction of the population formed pairs, composed of a female and a male that swam synchronously and close together for several minutes. During pairing the male often achieved gonopodial contact with the female. Black spotted males occurred in pairs ten fold more frequently than expected under random pairing. The major behavioral mechanism accounting for the disproportionate occurrence of spotted males in pairs is, probably, the preference of females for these males.