"2.8 billion prawn fingerlings at 1/10 of an ounce each equals 7,900 tonnes"
sounds about right. The 1985 Malaysian report (quoted by Emilez) shows that after 18 days of cage-net rearing prawn larva reach an average weight of 1.356g and an average length of 4.76cm (huge!), so the 1/10 oz= 2.8g you assume makes perfect sense.
If I just use an ASP of 20 USD/kg for tiger prawn, 7,900 tons mean a revenue of 158 Mill USD. That's more than 60% of total projected revenue for 2013. Wow...