A comparison of heterozygosity, sex ratio and production traits in two classes of triploid Penaeus (Marsupenaeus) japonicus (Kuruma shrimp): Polar Body I vs II triploids

Abstract

Current penaeid shrimp ploidy induction techniques allow the production of two different classes of triploid: Polar Body (PB) I triploids and PB II triploids. In the present study we quantified the heterozygosity at eight microsatellite loci of PB I and PB II full-sibling triploid Penaeus (Marsupenaeus) japonicus Bate (Kuruma shrimp) compared with full-sibling diploid controls in six separate families. Differences in harvest weight, survival from PL120 to PL210, sex at harvest age and gonad development in females at PL310 of the different triploid classes compared with diploid controls were also assessed for three families, two of which were also included in the heterozygosity assessments. We found no consistent trends in heterozygosity between the PB I and PB II triploids and diploid controls. Furthermore, no consistent trends in the harvest weight and no significant differences ( P > 0.05) in survival from PL120 to PL210 of shrimp in the different triploidy classes and diploid controls within each of the three families were observed when reared in controlled environment tanks. However, we demonstrate for the first time that PB I triploid P. japonicus are predominantly female with only two of the 34 individuals being male, both of which were from the same family. All 115 PB II triploids from the three families were female. We also demonstrate that PB I and PB II triploid females do not produce gonad tissue that is visible through the cuticle by the time they reach PL360, at which life-stage gonad is visible in sibling diploid controls. Provided commercial induction techniques can be developed, this study indicates that triploid induction has the potential to improve harvest yields through the production of predominantly female populations that are potentially reproductively sterile. Findings from this study indicate that there is no benefit in using the harder to perform PB I triploidy induction methods over PB II triploidy induction methods for commercial applications.