On the safety of RNAi usage in aquaculture: The case of all-male prawn stocks generated through manipulation of the insulin-like androgenic gland hormone

The recent introduction of RNA interference (RNAi) based biotechnology in aquaculture has aroused public awareness regarding safety aspects related to the use of such temporal transcript manipulation. In the present study, we demonstrate use of this biotechnology in large-scale production of all-male freshwater prawn Macrobrachium rosenbergii, relying on a two-phased approach. First, the insulin-like androgenic gland hormone (Mr-IAG) was silenced by dsRNA injections, causing sex-reversal of males into 'neo-females' (genetic males with female phenotype, with 86% success in this study). The next step involved mating the neo-females with normal males to produce all-male progeny. The administered exogenous dsRNA was fully cleared from the prawn's tissues after 7 days. Gene silencing through dsMr-IAG appeared to be temporary, with decay seen over time and nearly full expression of Mr-IAG (~ 82%) being restored after 28 days. Assessment of reproduction and fecundity in normal females versus neo-females revealed that in both groups, ~ 80% of the prawns were in a reproductive state and no significant difference was found in their reproductive output, either in terms of brood mass or number. Population structure, as indicated by the normal occurrence of male morphotypes, in both mixed-sex and all-male populations was examined in terms of weight and morphotype frequency distribution. The final harvest and marketing of the all-male prawn offspring occur about 19 months, i.e., one generation after the actual RNAi procedure. Thus, on top of the aquaculture yield advantage, the use of such RNAi procedure in crustacean aquaculture seems to be safe due to its temporary nature.