This book is a comprehensive elucidation of sex differentiation gonochoric and hermaphroditic fishes and explores it by examining it from sex chromosomes and sex determining genes, through sex differentiation genes and steroid receptor genes and to stem cells and germ cells. It (i) emphasizes the need to search for more than one sex determining gene residing on different chromosomes, (ii) evidences the brain sexualization of primary gonochores prior to sexual maturation from studies on transplantation of germ cells, endocrine sex reversal and gonodectomy, and for the first time indicates that gonadal differentiation implies the loss of bisexual potency of germ cells supporting somatic cells, (iii) traces the origin of hermaphrodites from secondary gonochores, (iv) explains the conservation of homologous sex differentiation and steroid receptor genes among gonochores and hermaphrodites (v) recognizes that the changes in the phenotypic morphotypes among gonochores is intrasexual but intersexual among hermaphrodites, (vi) identifies the optimal broodstock size, the appropriate candidate species for bait and food fishes and recognizes that the fishes do undergo menopause and reproductive senescence, which has an implication on the production of stem cells and (vii) shows that the analysis of steriles and mutants has demonstrated the value of fishes as a system for genetic dissection of human development and diseases. This volume is part of a series on Sex Differentiation in Fish-- Provided by publisher.