Triploid Black Tiger shrimp ( Penaeus monodon) performance from egg to harvest age

Abstract

In this study we induced triploids in a single family of Black Tiger shrimp ( Penaeus monodon) using chemical shock induction to stop the second meiotic division. The family was reared from egg to harvest age (post-larval stage 184) in a combination of commercial hatchery and experimental controlled environment tank rearing systems. During the rearing phase ploidy, survival, weight, sex ratio and gonad morphology of sibling diploids and induced triploids were periodically assessed. This is the first published report of the culture performance of triploid P. monodon. The induction rate of triploids at the nauplii stage was 83.4 ± 0.04% but this proportion had dropped to 62.45% by the time shrimp metamorphosed to the protozeal stage. Proportions of triploids remained fairly constant throughout the remaining larval and early post-larval stages (ranging from 60.47% to 72.38%), but dropped again to 56.32% by the time shrimp reached harvest age. The reduction in triploid rate from egg to harvest age is thought to be due to a combination of factors including heightened sensitivity of triploids to continual handling and general lower survival of triploids compared to diploids. Once shrimp reached harvest age diploid females were significantly heavier (42.95 ± 2.43 g, P < 0.05) than all other categories of shrimp. There was no significant difference in weight ( P > 0.05) between triploid females, diploid males and triploid males (35.14 ± 2.26 g, 34.02 ± 0.89 g and 31.79 ± 1.56 g respectively). The final sex ratio of harvest age triploid P. monodon was 1 female:1.625 males. Histological examination of harvest age female and male gonads revealed a drastic reduction in the development of both ova and sperm in triploid shrimp compared to diploids. The limited numbers of oocytes and sperm produced in triploids failed to fully mature by harvest age. No sperm were observed within spermatophores of triploids at harvest age when a gross morphological examination was performed and no sperm bundles were seen in the vas deferens. Using the same examination technique, diploid harvest age males had sperm within the spermatophores and vas deferens, and sperm bundles. Results indicate that reproductive sterility is likely for both female and male triploid P. monodon.