Can fish be vaccinated just by eating? NUS scientists target deadly virus wiping out farm stocks

SINGAPORE, June 29 — What if fish could be vaccinated just by eating their feed? 

Researchers at the National University of Singapore (NUS) are betting on exactly that to tackle a deadly virus threatening aquaculture stocks, The Straits Times reported today.

The team has developed an oral vaccine that can be mixed into fish feed to protect larvae and fingerlings, which are too small to be individually injected.

“Now, the fish will have the antibodies and so when the real virus hits, they will recognise this virus immediately and eliminate it,” NUS biological sciences professor Yang Daiwen was quoted as saying.

The target is the nervous necrosis virus,  a highly contagious infection that attacks the nervous system of fish and can wipe out nearly all larvae and juvenile fish it infects.

In current practice, vaccines are injected one fish at a time, a method researchers say is impractical for young fish and labour-intensive at scale.

Yang’s team said larvae face near 100 per cent mortality when infected, making early-stage protection critical for aquaculture survival rates.

The oral vaccine works by using virus-like particles that mimic the pathogen but carry no genetic material, triggering immunity without causing infection.

These particles are then wrapped inside the bacterium Lactococcus lactis, which protects them from stomach acid and delivers them into the fish’s intestines.

Once absorbed, the immune system produces antibodies, including neutralising antibodies that block the virus from infecting cells.

Yang said the protected version of the vaccine doubled antibody levels compared with unprotected particles and reduced viral load in the brain by about 300 times after exposure.

In grouper trials, vaccinated fish recorded survival rates of about 95 per cent compared with 60 per cent in unvaccinated fish.

The vaccine has so far been tested under laboratory conditions on Asian sea bass and grouper, both widely farmed in the region.

While promising, the oral version is still less potent than injectable vaccines and requires higher doses to achieve similar protection.

The researchers have filed three patents and are now preparing industry partnerships for field trials in commercial farms.

They are also exploring a similar oral vaccine approach for scale drop disease, another destructive fish virus affecting farmed species.