Scientists say virus behind high mortality rate of crabs

Scientists from the Central Institute of Brackishwater Aquaculture (CIBA-Chennai) on Wednesday officially announced that samples of wild crab (Scylla Seratta) collected from farms in Krishna district have been found to be infected with ‘white-spot virus’.

Presenting the results of their investigation on the wild crab to a group of 150 farmers here, CIBA Principal Scientist Dr. M. Poornima on Wednesday declared that the Scylla Seratta was infected with the white-spot virus and investigation was intensified to identify the source of the virus and issues associated with it.

Probe sought

CIBA scientists were asked by the State government to investigate the reasons for the mass mortality rate of the wild crab cultivated across the coastal belt in Krishna district.

Setback to aquaculture

According to Fisheries Department Assistant Director Mr. Suresh, the wild crab is being hatched in nearly 5,000 hectares in major locations of Machilipatnam, Krithuvennu, Koduru, and Nagayalanka in Krishna district and Repalle in Guntur district. The duration of the culture ranges between three months and six months based on the size of the seed.

The culture of wild crab became an alternative to shrimp cultivation, which was also hit by the white-spot virus earlier in Andhra Pradesh. Presently, 90% of the crab seed is being collected from the mangroves in Krishna and Guntur districts.

Temporary measures

The alarming rate of mortality of the wild crab in the farms since November 2018 became a major setback in the region’s brackishwater aquaculture sector, prompting the State government to swing into action to explore the scientific reasons for the mortality. “The crop holiday of 20-30 days between the two crops and chlorination of inflow water are strongly advised to minimise mortality. However, it’s a temporary solution to avoid mass mortality. The white-spot virus has been detected largely in the wild crab samples collected from the ponds in which shrimp was cultivated earlier,”Ms. Poornima, an expert in fish pathology, told The Hindu.

Nearly 90% of the production of wild crab from Andhra Pradesh is exported to South-east Asian countries. The Central government has granted an amount of ₹6 crore for setting up wild crab hatcheries at Suryalanka in Guntur district in 2017 but the development of the hatcheries hit a roadblock as the State government was yet to procure the land.