An investigation of maternal origin of morphometrically defined Tilapia species established in Sri Lanka

Three species of tilapia viz; Oreochromis mossambicus, Oreochromis niloticus and Tilapia rendalli, are well established in Sri Lanka and significant in fresh water fishery. Introgressive hybridisation is common between certain tilapia species producing hybrids that can obscure the morphological boundaries between species and also have numerous negative effects on long-term fishery. Therefore an easy index for identification of tilapia species and their hybrids in the field, which is based on morphometry of tilapia fish is essential. However, such a morphological index substantiated by DNA based study is not available. The present investigation reports the most important morphometric characters for the identification of tilapia species in Sri Lanka. The maternal origin of selected individuals of such groups was determined using heteroduplex formation of PCR products of a part of control region of mitochondrial DNA (mtDNA) with the PCR product of the same region of an authentic O. mossambicus. The majority of individuals tested had maternal origin conforming to the present morphologically defined species, whereas a few (03) O. niloticus individuals had mossambicus maternal origin indicating hybridisation.