Genetics Explained Mike Sipe Graphics of Sex Determination Genes When I first got started with the production of Pure line breeders the two species now known as tilapia mossambica and tilapia horonorum, were known as tilapia mossambica (mossambic) and tilapia mossambica (zanzibar). They were considered such close relatives that they were grouped as two sub species and so the varieties were designated by where they came from. During this time the determination of species was not made by using any DNA markers and only the "science" of meristics was used to determine the species. Since the "science" of meristics was based on such things as gill rakers, which meant counting and typing the gill rakers in each fish. What is more, is that when the number of spines on the Dorsal fin or any other physical characteristics that could be easily counted was used, the job of determining the species of a live fish was difficult because one had to hold the speciman still while the counting was done and needless to say the fish rarely cooperated so the time it took to verify that a group of fish was one speicies or another could be several weeks and even then when a fish looked exactly like another fish, taxonomist tended to group them in the same species. Read More...