In this project four microsatellite markers and a mitochondrial DNA (mtDNA) gene fragment were used to investigate possible causes of a reported decline in productivity of GIFT in PINs. Results indicated that genetic diversity had declined marginally compared with a GIFT reference stock from Worldfish Centre. In addition, there was little evidence found for introgression from feral tilapia populations. Loss of genetic diversity most probably resulted from practices where operators had not managed genetic resources adequately in the hatchery. While GIFT had been considered an improved line of Nile tilapia (Oreochromis niloticus), mtDNA analysis revealed haplotypes assigned previously to three discrete Oreochromis species (O.niloticus, O.mossambicus and O. aureus) were present in both the Fiji strain and the Worldfish Centre strain.
Specifically, the assessment of samples from Naduruloulou Research Station (NRS) in Fiji revealed that the broodstock currently used is a stock introgressed with O.niloticus, O.mossambicus and O. aureus genes. This supports the genetic introgression hypothesis. However the GIFT samples from Worldfish Centre in Malaysia showed that it was also a mixture of these three distinct species (and not based purely on O.niloticus crosses). The research team therefore hypothesised that the symptoms or assumptions of the presence of non-Nile tilapia haplotypes in the NRS hatchery was not due to introgression following flooding events and inadvertent hybridisation or unintentional selection in Fiji. Similar results were obtained from assessment of broodstock samples currently used at Aiyura, PNG except for samples from Potsy farm that showed only evidence of poor hatchery practices.
The reported presence of red morphs was more difficult to explain, however, it was evident that O.niloticus and O.mossambicus had hybridised either before or during the development of the GIFT strain in Philippines and maybe alleles for red colour had introgressed the GIFT strain at this time.
The project included workshops on broodstock management and other aspects of tilapia culture as per requests from local government officers at NRS. Participants now recognise the need to actively manage the genetic quality of fish stocks and to maintain a large number of broodstock (to be produced from as many families as practically possible), and to provide appropriate quality and quantity of feeds to maintain their productivity. They also acquired and practised hatchery skills. They also learnt how to prevent the introduction of inferior tilapia species into brood ponds, to eliminate of poor quality individuals and to adopt an independent culling-selection process for non-desired stocks.
Based on the results of genetic analysis the project team did not recommend immediate introduction of new GIFT stocks from Worldfish Centre. However they highlighted the urgent need for training hatchery operators in PNG, Samoa and Vanuatu and improving hatchery facilities and extension services to private hatchery operators regarding nutrition and stock management practices.