January 29, 2010

Asian group makes progress in aquaculture vaccines

Technologies and vaccines to control the viral nervous necrosis (VNN) disease in profitable aquaculture species have been developed by researchers at the Aquaculture Department (AQD) of the Southeast Asian Fisheries Development Centre (SEAFDEC).

The new methods could increase production and cut losses in the aquaculture industry, according to researchers Leobert de la Peña and Rolando Pakingking, Jr.

VNN, or viral encephalopathy and retinopathy (VER), has been causing great economic harm to producers of high-value fish at the larval, juvenile and grow-out stages for the past 20 years, Pakingking said.

There is a pressing need for preventative measures like selecting disease-free broodstocks, disinfecting eggs to control the vertical transmission of the virus from broodstocks and vaccinating for immunity, said de la Peña.

The researchers artificially contaminated fish eggs with VNN and either washed them with ozone-treated seawater or immersed them in iodine and Virkon. The eggs were tested for the virus before and after the process and post-disinfection with the polymerase chain reaction (PCR) test and cell culture.

Experiments showed the effective time exposure and concentrations using ozone-treated seawater, iodine and Virkon were 2.5 minutes, 25 parts per million (ppm) and 1.5 ppm, respectively, de la Peña said. His study also determined that groupers were susceptible to the disease while milkfish and siganid were not.

Grouper larvae weighing 8g or less were highly vulnerable, with a mortality rate of 80-100% in four to eight days. Fish weighing 90g or more were not susceptible.

The group at most risk was vaccinated, and de la Peña said fish vaccinated with 100 ng had the highest survival rate.

Pakingking and others meanwhile developed a formalin-inactivated vaccine to manage infection at the grow-out stage. Three studies on the vaccine's efficacy ran from June 2007-November 2009 under the project "Fish Disease Surveillance System".

The first study measured the responses of Asian sea bass to a formalin-inactivated betanodavirus vaccine. These fish created neutralising antibodies at high titer levels from day 10-116, with the highest level at day 60. No deaths occurred after the vaccinated fish were injected with the red-spotted grouper nervous necrosis virus.

The second study tackled the vaccination of the brown-marbled grouper and the third examined the susceptibility of hatchery-reared pompano to betanodavirus and its immune responses to a formalin-inactivated betanodavirus vaccine.

The Southeast Asian Fisheries Development Centre (SEAFDEC) is an intergovernmental organisation established in December 1967 for the purpose of promoting sustainable fisheries development in the region. Its current member countries are Brunei, Cambodia, Indonesia, Japan, Lao PDR, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Vietnam.