Genetic variation among four bred populations of two tilapia strains, based on mitochondrial D-loop sequences.

The hybrid between Nile tilapia (Oreochromis niloticus,♀) and blue tilapia (O. aureus,♂) is an important strain in Chinese aquaculture industry. Two populations named AF (O. aureus, 29 samples) and NF (O. niloticus, 22 samples) were gathered from Freshwater Fisheries Research Center (FFRC). The other two named AG (O. aureus, 29 samples) and NG (O. niloticus, 28 samples) from Guangxi Fisheries Research Institute (GFRI). GFRI introduced AG and NG from AF and NF. The mitochondrial DNA D-loop was sequenced to assess the genetic diversity among four populations. A 580 bp fragment was sequenced. The 93 variable sites defined 39 haplotypes and three were shared. As a result, the genetic diversity of O. aureus AF and AG was much lower (H=0.497-0.532, K=0.69-0.714, π=0.0012-0.00124) than that of O. niloticus (H=0.849-0.866, K=24.286-24.807, π=0.04246-0.04337). Furthermore, the indices (H, K, π and D) was a slight increase between AF and AG, so did NF and NG. These results indicated that as the male parent, the AF and AG population was purebred and sustainable. And as the female parent, NF and NG had high genetic diversity. The conclusions might give reference to keep the germplasm diversity of tilapia and other introduced fishes.