Dynamics of reproduction in a captive shrimp broodstock: Unequal contribution of the female shrimp and a hidden shortage in competent males

The major bottleneck in the breeding in captivity of penaeid shrimp is the fact that females do not spontaneously undergo vitellogenesis, which thus has to be induced endocrinologically by eyestalk ablation. Partial compensation for the low responsiveness of the females to this treatment is obtained by the use of very large broodstock populations. This old problem was newly approached in the current study by monitoring individual female life-spans and vitellogenic cycles in a small population of the Pacific white shrimp, Litopenaeus vannamei. Vitellogenic activity and spawning peaked during the second month of the four-month trial and decreased thereafter due to the sharp fall in the number of reproductively active females. Only about 75% of all the females in the broodstock were reproductively active, and most of them spawned for the first time, or exhibited fully vitellogenic ovaries, during the first two weeks post-ablation. Nevertheless, the best performing females, which comprised less than 20% of the female broodstock, matured more rapidly, exhibiting fully vitellogenic ovaries 4.1±3.4 days after eye-stalk ablation. These animals contributed more than 50% of the total eggs and nauplii produced. The total number of vitellogenic cycles recorded from all reproductively active females was 305, but in less than a third of these cycles were the females observed to be carrying spermatophores or sperm masses. Since females-but not males-in captivity undergo accelerated reproductive cycles due to the endocrine induction, it is suggested that the lack of mating consistently reported from maturation systems may be due to the lack of sufficient ready-to-mate males.