The effect of Penaeus merguiensis densovirus on Penaeus merguiensis production in Queensland, Australia L Owens, K La Fauce and K Claydon School of Veterinary and Biomedical Sciences, James Cook University, Townsville, Qld, Australia Abstract Penaeus merguiensis densovirus (PmergDNV) is currently present on several Queensland prawn farms culturing Penaeus merguiensis. Densoviruses have been linked to mortality and stunting that has caused significant financial loss to prawn farms in Asia. A histopathological study for PmergDNV was initially undertaken to compare broodstock to grow out factors from 60 broodstock animals from each of 22 ponds. There was a significant negative cor- relation (r = )0.61) between the number of animals with PmergDNV lesions and healthy animals. Furthermore, a higher number of septic hepato- pancreatic tubules was correlated (r = 0.48) to high PmergDNV loads. Hence, a polymerase chain reaction analysis of 10-day-old post-larvae (PL) was conducted to determine whether PmergDNV infection was resulting in production losses. An attributable risk analysis of PL from 190 ponds over a 2-year period revealed that 28–29% of ponds with below average survival will have at least average survival following the removal of or decreased levels of PmergDNV. P. merguiensis culture facilities in Queensland should have at least a 14.5% increase in production, equating to an increase of $2.25 mil- lion within the first year alone, following the removal or reduction of PmergDNV in their ponds. Hence, focussing efforts on prevention, better management practices and maintaining healthy stock should be of top priority. Keywords: aquaculture, attributable risk, densovi- rus, disease, Penaeus merguiensis densovirus, prawns. Introduction Aquaculture continues to be an important compo- nent of Australian fisheries production. Prawns are the dominant crustacean species farmed in Australia and include the black tiger prawn, Penaeus mon- odon, banana prawn, P. merguiensis, brown tiger prawn, P. esculentus, and kuruma prawns, P. japo- nicus (Lobegeiger & Wingfield 2007). The value of prawn aquaculture production initially increased from 990 t, estimated at $35 million in 1996–97 (ABARE 1997), to peak at $65 million in 2001–02 (ABARE 2003) before falling close to $50 million in 2005–06 (ABARE 2007) and even further to $44.2 million in 2007–08 (ABARE 2009). The value of the Queensland component of the cultured prawn industry alone was estimated to be approx- imately 93% of the whole aquacultural prawn industry at $46.5 million (ABARE 2007). Unfor- tunately, during the years of increasing production, there was an associated increase in disease problems, particularly those with infectious aetiologies (Light- ner & Redman 1992). Among these, viral patho- gens have contributed to substantial economic losses within penaeid culture (Fraser & Owens 1996; Flegel 1997) and are recognized as a major constraint in Queensland prawn farming. Hepatopancreatic parvovirus (HPV) belongs to the family Parvoviridae, is non-enveloped and con- tains a linear, single-stranded DNA genome approx- imately 6 kb in size encoding one structural and two non-structural proteins (Siegl, Bates, Berns, Carter, Kelly, Kurstak & Tattersall 1985; Berns, Bergoin, Bloom, Lederman, Muzyczka, Siegl, Tal & Tattersall 2000). It was first visualized in wild P. merguiensis and P. indicus in Singapore (Chong & Loh 1984). Less than a year later, it was reported in P. semisulc- atus from Kuwait and in P. monodon and P. chinensis Journal of Fish Diseases 2011, 34, 509–515 doi:10.1111/j.1365-2761.2011.01263.x Correspondence K La Fauce, School of Veterinary and Bio- medical Sciences, James Cook University, Townsville, Qld, Australia, 4811 (e-mail: kathy.lafauce@gmail.com) 509 Ó 2011 Blackwell Publishing Ltd