Sexual maturity can double heart mass and cardiac power output in male rainbow-trout

Mature male rainbow trout have significantly higher relative ventricle masses (RVM, ventricle mass as a percentage of body mass) than do immature males or females. Hatchery-reared maturing male trout had a mean RVM of 0.139%, whereas females had an RVM of only 0.074%. Moreover, as males matured and their testes grew from 0.07 to 3.92% of body mass, RVM more than doubled. In female trout no such heart growth occurred; RVM remained unchanged during the period of ovary growth