The Penaeus monodon baculovirus (MBV): Its epizootiology, prevention and control in penaeid shrimp hatcheries and grow-out ponds in the Philippines.

Abstract

The prevalence of Penaeus monodon baculovirus (MBV) in black tiger prawn (Penaeus monodon Fabricus) was investigated based on 372 diagnostic cases examined from October 1989, to December, 1990. Laboratory transmission of MBV to the different life stages of P. monodon and tolerance of MBV in infected hepatopancreatic tissues to chemicals and extreme environmental conditions were studied. A comparative assessment of the growth performance, survival and food conversion ratio between MBV-infected and non-infected populations of P. monodon was investigated and a new technology called Strategic Egg Prophylaxis (SEP) in the production of MBV-free P. monodon postlarvae was developed and tested. MBV was the most prevalent viral disease of P. monodon accounting for 67.1% of all diseases diagnosed in this species, and was widely distributed in all 12 major shrimp farming provinces in the Philippines throughout the year. The nauplii and zoea larval stages were refractory to MBV infection within 12 days post inoculation, but the mysis larval and the postlarval stages were susceptible to MBV infection within 6 and 2 days post inoculation, respectively. Cumulative mortality was significantly different (α = 0.05) between the MBV-infected and unexposed control groups of mysis larval and postlarval test shrimps. No significant growth rate differences were observed between the MBV-infected and unexposed control groups of larvae and postlarvae. MBV was resistant to 150 ppm iodine, 1:100 dilution of peroxygen/organic acid compounds and 10 ppm calcium hypochlorite at 240, 240 and 480 min of exposure, respectively, and to freshwater and at 37°C for 240 min. Direct exposure to sunlight for 240 min inactivated MBV in the hepatopancreatic tissues. In pond cultured P. monodon populations, the MBV negative stocks grew by as much as 43.4%, 20.8%, 13.7% and 13.7% more than the MBV-infected stocks at densities of 30/m², 20/m², 18/m², and 10/m², respectively over a 126 day growing period. Mortality was significant in MBV positive stocks affected with protozoan and bacterial shell disease. Food conversion ratio (FCR) was not a significant factor among MBV negative and the MBV infected populations. MBV negative P. monodon postlarvae were successfully produced using the Strategic Egg Prophylaxis (SEP) by washing and rinsing P. monodon eggs with iodine, benzalkonium chloride, calcium hypochlorite or ozone-treated seawater. The eggs washed with ozonized and benzalkonium chloride-treated seawater gave higher hatching rates of 72.4% and 60.3%, respectively. Postlarval survival at PL-7 was 67.6% in eggs washed with ozonized seawater and 42.3% in benzalkonium chloride-treated seawater. The unwashed control groups developed MBV infections starting at PL-7 stage.