A study of growth curves of common carp of the Chinese and European races was aimed at gaining more understanding of the genetic and developmental interrelations between growth and sexual maturation. A negative association between growth rate and onset of sexual maturity was noted particularly in the Chinese race. Gonad development in males of the Chinese race is faster, and starts earlier, than that of the European race. The Chinese x European crossbred shows incomplete dominance in the direction of the European parent for this trait. Heterosis for growth under harsh conditions (as of the Chinese parent) and slow sexual development (as of the European parent), acting together, result in over–all heterosis of the Chinese x European crossbred. Copyright © 1985, Wiley Blackwell. All rights reserved