Genetic diversity status of White shrimp Penaeus (Litopenaeus) vannamei broodstock in Mexico

The Mexican shrimp culture industry is based upon Penaeus (Litopenaeus) vannamei broodstock with a presumed common genetic origin and more than 10 generations of closed breeding. This has raised concerns about the low level of genetic diversity and accumulated inbreeding in these broodstock. Inbreeding depression can lead to low performance of hatchery-reared shrimp, and an evaluation of the genetic diversity can significantly enhance broodstock management. In this study, we evaluated the genetic composition and diversity of broodstock from six hatcheries from Northwestern Mexico, and estimated their inbreeding levels based on DNA microsatellite markers. A total of 658 individuals were analyzed with six microsatellite loci. Medium mean genetic diversity values (8.98 alleles per locus) and heterozygosity (0.57) were higher than anticipated. There was significant variation in the genetic composition of broodstock from different hatcheries. All the hatchery broodstock were significantly different from a wild population from the state of Sinaloa. The most common alleles were the same in broodstock from all six hatcheries. None of the hatchery stocks has uniquely distinctive alleles. Broodstock management appears to have maintained genetic diversity, because mean allele numbers were similar to the pooled values from a single hatchery sampled between 2000 and 2002. However, with an observed heterozygosity (Ho) below Hardy–Weinberg expectations and a high mean inbreeding coefficient (26.5%) it would be timely to introduce cross breeding among hatcheries to reduce the risk of inbreeding depression.