THE EFFECT OF VISUAL DENSITY ON THE FECUNDITY OF THE GUPPY, POECILIA-RETICULATA

This paper examines the effect of visual density on the brood size of female guppies, Poecilia reticulata. Previous laboratory studies of gu ppies showed that the fecundity of females decreases as density increa ses. In the present study, the effect of visual density was examined u nder conditions where detrimental factors such as interaction of indiv iduals, waste substances, and dissolved oxygen were constant. The broo d size of females at visual densities of 4 or more individuals was sig nificantly larger than at zero visual density. There was a significant positive correlation between brood size and visual density. Sex ratio did not significantly affect brood size. Guppies can recognize surrou nding densities and change their own fecundity in response to changes in density.