An optimized group mating design and determination of the admixture rate in Nile tilapia families

• An optimized group mating design for family development in Nile tilapia.
• The survival rate of embryos after gastrula stage outside the mouth in aerating water is high.
• For group mating systems there were no mixed individuals in most families according to the paternity analysis.

The Nile tilapia is the most productive and internationally traded food fish in the world. Many Nile tilapia families are needed to develop breeding programs for this species. The aim of this study was to develop Nile tilapia families using the Oreochromis species unique breeding characteristics (male territory establisher and female mouth brooders) and determine the mixing rate within each family. Both male and female fish were cultured in one pond in the reproductive season and the female mouths were checked every 5–8 days. When embryos were present, they were removed and cultivated independently as a family. As a result, 45 families were developed from the 60 female fish sampled. The embryo survival rate in aerated water varied from 85.5 to 100.0%. Seven polymorphic microsatellite loci were selected from a set of 31 for paternity identification. The CPE (combined paternity exclusion probability) of two microsatellite loci was higher than 0.93 and the CPE for the seven loci used in this study was as high as 0.9999. There were no unrelated individuals in five of the seven families analyzed and only one mixed individual in F29 and F30. The overall admixture rate was very low (2.2%). In this study, we developed an optimized group mating system. Furthermore, we verified that for group mating systems there were no mixed individuals in most families and the admixture rate of some families was very low according to the paternity analysis.