Female penaeid prawns grow faster and may have higher feed conversion efficiency than do males.  If a technique could be devised to bias the sex ratio of larvae produced so that the proportion of females in each brood outnumbered the males, the commercial grower could achieve dramatically improved production.

To enable control of larval sex ratios, the goal of this grant was to identify the genetic material in prawn chromosomes that triggers development into a male or female prawn.  Once it is possible to identify the genes controlling the sex of maturing prawn larvae, those genes can be targeted and manipulated through molecular techniques.

Genetic and chromosomal sex determination is not understood in most crustacean species.  Penaeid prawns possess numerous, uniformly small chromosomes so that potential sex chromosomes have never been identified with classical karyotypic microscopic studies.  Molecular genetic techniques provide a new tool for increased resolution of sex-determining factors.

We studied two cohorts of genetically inbred prawns to directly reduce the natural genetic variability between individuals and to further accentuate the genetic variability between the sexes.  The first experimental group was bred from a match between two wild-caught Penaeus monodon.  The offspring from this mating were all siblings (an F1 generation).  These prawns were grown by Dr. David Hewitt and Mr. Shane Hansford at Bribie Island Aquaculture Research Centre.  The second experimental group was bred from another commercial species, Penaeus japonicus.  Dr. Nigel Preston and Dr. Peter Crocos supplied an F2 generation from pond-reared prawns grown at the CSIRO Marine Laboratories in Cleveland.  Creating a genetically inbred F2 generation requires more time because two wild caught Penaeus japonicus are mated to obtain F1 offspring.  Then two siblings from the F1 experimental group must be raised to maturity and bred so that their offspring possess increased genetic similarity, as an F2 generation.

Our studies revealed an unexpectedly high genetic variability between individuals of the same prawn species.  Further, we discovered that prawns use a system of genetic sex determination that is distinct compared to the chromosomal organisation of most well known organisms.  

Keywords: Sex determination, penaeid prawns, Penaeus monodon,  Penaeus japonicus, cell culture, aquaculture.