Heart growth associated with sexual maturity in male rainbow trout (Oncorhynchus mykiss) is hyperplastic

Ventricle mass increases, relative to body mass, with sexual maturity in male rainbow trout. It is net known whether this increase is due to hyperplasia or hypertrophy. We examined this question in hatchery-reared male and female rainbow trout over a 16-week study. Fork length, body, heart (ventricle), and gonad mass were recorded. Ventricles were analyzed for DNA, RNA, and protein content. We confirm that ventricle growth occurs in males but not in females. There was a slight but significant decrease in protein content of hearts from male trout with increasing heartsomatic index but protein content did not change in hearts from female trout. There was no change in RNA/protein ratio in either male or female trout hearts indicating that increased protein synthesis in male trout hearts was due to an increase in RNA activity. The DNA/protein ratio showed a significant increase in male trout hearts, but no change in female trout hearts. We conclude that the major part of the increase in ventricle mass in male trout hearts is due to hyperplasia. (C) 1997 Elsevier Science Inc.