Feasible options to restore genetic variation in hatchery stocks of the globally important farmed shrimp species, Litopenaeus vannamei

The white shrimp, Litopenaeus vannamei, a species endemic to Latin America, is now being cultured around the Pacific. L. vannamei aquaculture comprises about 80% of global shrimp aquaculture production and as such, it is noted to be important to the economy of various temperate and tropical countries. This globally important species is highly fecund (where only a few broodstock are needed to produce the next generation), and while it has been subjected to stock improvement through mass selection, L vannamei farms, for the most part, lack pedigree records. These aforementioned factors can lead to small effective population (Ne) sizes, which may then cause loss of genetic diversity in hatchery stocks. We have assessed levels of genetic diversity among L. vannamei samples derived from seven hatcheries across the Pacific Ocean, using three different measures of genetic variation, namely, DNA microsatellite alleles, mtDNA haplotype variation and genomic SNPs. We have compared levels of the aforementioned variation among hatchery samples with wild caught Mexican samples. All measures of variation were lower in the hatchery samples compared to wild samples. Ne estimates from the hatcheries were lower than 50. For other highly fecund marine species we earlier found that hatchery lines had lost variation, but the variation lost in each line tended to be sufficiently different from each other such that variation approaching that of the wild could be restored by line crossing. This method would be preferable, in terms of maintaining existing genetic gains, rather than simply introgressing diversity from the wild. Our goal here is to test if a similar possibility exists for L. vannamei stocks. Indeed we found that samples from different L. vannamei hatcheries around the Pacific were likely to differ in the types of genetic variation they retained, so variation approaching that of the wild may potentially be restored by crossing different hatchery lines.