Abstract
Heritability for dorsal fin ray number in the guppy, Poecilia reticulata (=Lebistes reticulatus) was estimated by sire-offspring, dam-offspring, and mid-parent-offspring regression at both 19 and 25 C. Heritability ranged from 0.23 to 0.77, and five of the six estimates were significantly different from zero (P = 0.05). Heritabilities were higher at 25 C. Sire estimates of heritability were higher than dam estimates of heritability. The high heritabilities explain how meristic traits can change through selection or other driving forces in evolution