Feasibility of Ripening Penaeus monodon by using Pheretima tschiliensis as a Bait and its Verification by Vitellogenin Gene Expression

Traditional broodstock diets, being susceptible to virus attacks or carrying the virus to parent shrimps, bring a huge bio-security risk to shrimp breeding. This study was carried out to determine the feasibility of Pheretima tschiliensis as a replacement of traditional bait to accelerate the maturity of parent shrimps of Penaeus monodon, which was verified by the dynamics of vitellogenin gene expression in hepatopancreas and ovary of P. monodon. The parent shrimps fed on four different diets including commercial parent shrimps feed (Diet A), Pheretima tschiliensis combination bait (Diet B), Pheretima tschiliensis (Diet C) and Nereis succinea combination bait (Diet D), and the effect of each diet on the maturity of parent shrimps was evaluated by testing the gonad weight increase rate, eggs amount, average spawning time and levels of VTG mRNA expression. The results showed that P. tschiliensis, as a closely related terrestrial species of N. succinea, had the best effect on maturation of parent shrimps. The highest gonad weight increase rate of 1845.28% and the largest consecutive spawning rate with average value of 70.66% were both in groups fed on P. tschiliensis, with no significant difference from the groups fed on N. succinea combination bait. The dynamics of VTG mRNA level were observed in hepatopancreas and ovary of P. monodon with the trend of increasing firstly and then decreasing, which reflected reproductive performance of the parent shrimps and was suggested to be an indicator of reproductive performance for selective breeding. As a result, P. tschiliensis is a suitable substitute of N. succinea based on its effect on the reproductive traits and VTG mRNA expression level in parent shrimps of P. monodon.