Novel virus may explain fry mortality in Ballan wrasse
A novel virus in Ballan wrasse hatchlings could be the cause of unexplained high mortality for hatchlings, according to fish health research business Patogen.
The Norwegian-based company has named the virus Ballan wrasse birnavirus (BWDV).
Patogen worked with a fish farmer to investigate diseased fish for relevant pathogens and histology, and performed a full genome sequencing in which researchers found the genome of the novel birnavirus. Downstream PCR studies detected large amounts of virus in fish larvae from groups with increased mortality. PatoGen believes that biosecurity measures against BWDV will reduce the mortality in this critical phase of the ballan wrasse production.
The mortality for wrasse occurs after a short period of loss of appetite and peak mortality typically occurs between day 17 and 25 post hatching (DPH).
Samples from fish at the farm were collected weekly from hatching and were examined with PCR for relevant pathogens and histology. The genome sequencing analysis revealed high amounts of gene sequences of a novel virus grouped within the virus family Birnaviridae. The gene sequences of the novel Ballan wrasse virus were genetically different from other known birnaviruses and aquabirnaviruses.
The best known birnavirus in Norwegian aquaculture is Infectious pancreatic necrosis virus (IPNV), an aquabirnavirus known to cause fry mortality in Atlantic salmon. Other birnaviruses are associated with early fry mortality on other marine fish species.
The investigation showed that the virus infection is maintained in the population for a long time after the peak mortality and at high levels.
PatoGen is now offering fish growers a PCR analysis for the Ballan wrasse birnavirus.