An attempt to estimate the magnitude of additive genetic variation of body size in the guppy-fish, Lebistes reticulatus.

Two experiments in Lebistes reticulatus were performed: a pilot selection experiment continuing for only two generations, and an experiment designed to estimate heritability from the correlation between full and half sibs. No response was obtained in the selection experiment. The character selected for was weight at 42 days. In the second experiment weight at 42 and 63 days and length at 28, 42 and 63 days were measured. In this experiment a component of additive genetic variation significantly greater than zero was demonstrated for only one of the characters, length at 63 days. It was not possible to detect this component of variance until part of the variation due to environmental differences between aquaria had been removed from the total variation.