California sheephead, Semicossyphus pulcher, is a protogynous sequential hermaphroditic temperate marine fish found in different groups of individuals with different average water temperature exposure. In these populations some females transition sex, generally undergoing a significant increase in body mass and converting ovaries into testes as they become males. Multivariate analysis we of nine populations based on average slow myosin heavy chain (MyHC) expression, average water temperature exposure, average body mass, sex ratio and population density separated northern and more offshore populations apart from southern and coastal populations. In addition I observed a relationship between MyHC, a major muscle contractile protein, expression and average water temperature exposure, increased body mass, sexual transition and fiber type. The results of my study highlight the complex relationship between sheephead muscle physiology and the environment, individual development, behavior and fiber type.