This book is the first to report that research in allogenics/xenogenics has conclusively shown that fishes have retained bisexual potency even after sexual maturity and spermiation. The XY genotype found in the unexpected female phenotypes sired by supermales (Y¹Y²) and androgenic males (Y²Y²) points out the need to employ sex specific molecular markers to identify the true genotype of a juvenile, which matures either as a male or female, depending upon the sex of its pair (female or male) and thereby critically assessing the environmental role in sex determination. This book is meant to assist molecular biologists in the search of sex determining gene(s), fishery biologists endeavouring to develop techniques for profitable monosex aquaculture and ecologists interested in conservation of fishes and their genomes.