Reproductive output in Pacific white shrimp Litopenaeus vannamei is highly variable with a small portion of broodstock (<20%) often accounting for a majority of larval production in commercial hatcheries. Previous studies have shown that reproductive traits are heritable and heritabilites, while not high, are typically sufficient to justify genetic improvement via selective breeding. However, reproductive traits display a high level of phenotypic variation, and this variation makes selection efforts difficult, as large samples sizes are required to generate meaningful estimates of genetic merit using traditional selective breeding approaches. In addition, selection accuracy, and therefore genetic gains, is limited since estimates of family genetic merit can be poor predictors of genetic quality for individual breeders, as evidenced by the low/moderate heritability of reproductive traits. Recent advances in genomics (e.g. commercial availability of high-density SNP panels) offer breeders the opportunity to improve the efficacy and efficiency of shrimp breeding programs using genomic and/or marker-assisted selection. These approaches can be particularly useful for hard-to-measure and low/moderate heritability traits (like reproductive traits). The goal of this project is to use genomics to investigate reproductive performance of L. vannamei and includes conducting genome-wide association studies (GWAS) and genomic selection (GS) on multiple reproductive traits.
Broodstock representing 23 families (PGen) from the Oceanic Institute of Hawaii Pacific University (OI) breeding program were sampled for genotyping (50K SNP panel) and stocked into four (4) maturation tanks at OI with each tank receiving ~110 males or females. Sourcing and natural mating of mature females was carried out on 57 days during a 70-day maturation cycle. Data were collected on each female (or spawn) and included: # of maturation events, # matings, # spawns, eggs spawned, and viable nauplii produced.
Fifty-one (51) of the spawns were randomly selected for production of G0 families. Tagged juveniles (~160) from each G0 family were combined into a common tank (75-m2 raceway) for growout evaluation. When shrimp reached ~20 g, 20 males and females from each family were selected as candidate broodstock, tagged (colored, numbered eyestalk tag), and sampled for genotyping. Samples were genotyped (50K SNP) and individual genomic breeding values were calculated for each candidate broodstock. High-ranking candidates representing 27 G0 families were grown to broodstock. These shrimp are currently undergoing reproductive evaluation at OI.
For Pgen broodstock, a total of 480 maturation events, 363 matings, and 321 spawns were recorded. There were 75 females (out of 221) that did not spawn. Of these, 53 never matured and 16 matured but did not mate. The most productive females, with regard to # spawns and total egg production, spawned 6 and 7 times and produced 1,440,000 and 1,434,286 eggs, respectively. Additional results (incorporating G0 spawning data) including GWAS and genomic selection for # spawns and eggs/spawn will be reported.