Researchers gain understanding of shrimp virus

Aquaculture researchers from National Taiwan University (NTU) say that genetic analysis is yielding new insight into the workings of a virus that has devastated shrimp stocks in the nation since it was discovered in 1992.

Although her team is working on a way of inoculating shrimp against the dreaded White Spot Syndrome Baculovirus Complex(WSSV), aquaculture researcher Lo Chu-fang said that there was much Taiwanese shrimp farmers could do to overcome the disease through better aquaculture practices.

"We found that during periods of stress, the level of WSSV increases in the shrimp's body at an astonishing rate," Lo said. "For instance, we have observed virus levels increasing 100,000-fold during spawning, which is a stressful event."

Local shrimp-rearing methods put a lot of stress on shrimp stocks because local shrimp farmers tend to adopt a very intensive approach, Lo said.

"We are talking about keeping up to a million shrimp per hectare of aquaculture pond whereas abroad 300,000 to 400,000 is the norm," Lo said.

She said that not only were crowded shrimp more susceptible to WSSV, the conditions may have actually caused the condition in the first place.

"WSSV did not appear until 1992," said Lo, who has been working on the virus for many years. "Our research found that previously the virus was an obscure and largely harmless one affecting certain species of crab."

However, once the virus started affecting farmed shrimp, it spread rapidly.

"They say that WSSV spreads as the wind blows," Lo said.

Major asian shrimp production areas are affected, including Thailand and China. However, Australia remains unaffected by WSSV.

Lo's research, which includes the discovery of a way of testing for WSSV, has helped some shrimp producers abroad drastically reduce losses to WSSV from up to 80 percent to less than 5 percent.

Paradoxically, Taiwanese producers have been slower to adopt the researchers' advice, Lo said.