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AsianScientist (Jan. 28, 2022) – Millions of dead fish wash up on the coastal shores and river banks across the world every year, with their tails and bellies exposed. Their death exposes a sinister problem—toxic waters.

The rampant fish kill often points to the environmental stress such as chemical toxicity and lack of oxygen in the waters, or the invasion of pathogens like bacteria and viruses into the fish populations.

These disease-causing agents lead to a myriad of symptoms from mouth sores and missing scales to erratic behaviors like gasping at the water’s surface. Globally, such outbreaks are estimated to cost the aquaculture industry US$6 billion annually. This is particularly significant for Asia because the region is the largest producer and consumer of sea food.

Besides biodiversity losses, unbridled disease spread poses a threat to the fishing industry and consumer food supply. For Dr. Jeffrey Seng, fish microbiologist and Senior Lecturer at Nanyang Polytechnic (NYP) in Singapore, one solution may lie in a technology that is on top of everybody’s mind at present: vaccines.

Vaccinating fish to address infection isn’t exactly new. According to Seng, salmon caught from the shores of Norway are typically injected with at least seven different types of vaccines. In contrast, despite Asia’s thriving seafood industry, there is a dearth of fish vaccine companies in the region.

“Norwegian and other Scandinavian organizations specialize in vaccines for temperate water pathogens, but not necessarily for pathogens found in tropical climates,” said Seng, who has a background in fish virology. “In Asia, we eat many different types of fish and they may all have different vaccination needs.”

Given this unmet need, Seng is at the forefront of advancing the development of ‘customized’ vaccines, also called autogenous vaccines, that are better suited to the diverse fish population in Asia.

Just as how the COVID-19 vaccines come in different forms from messenger RNA to inactivated virus, fish vaccines can also be made using various elements such as an expression system that mimics viral protein production.

Seng’s team extracts the pathogen from the infected fish then analyzes the pathogen’s features like genetic data or surface proteins, which are relevant to the microbe’s survival and disease-causing behavior.

By dissecting the pathogen’s molecular landscape, they can formulate vaccines specifically designed to elicit an immune response, effectively teaching the fish to recognize and attack the pathogen.

One of Seng’s biggest successes involved creating a vaccine against the bacterial strain Tenacibaculum maritimum, which causes fish skin infections. The strain had been spreading rapidly in aquaculture firm Barramundi Asia’s farm in Singapore, destroying up to 90 percent of the the Asian seabass population.

Backed by Barramundi Asia, he and his NYP colleagues dove into the bacteria’s molecular world. They leveraged novel biotechnologies to characterize the strain and to figure out how to stop the microbe from causing and spreading the disease.

After extensive testing to ensure effectiveness and safety, the team deployed the vaccine at the Barramundi Asia farm and saw the fish mortality rate eventually drop to just five to ten percent—a huge success.

Most commercial vaccines take years to enter the market. But Seng hopes that the development of autogenous vaccines can be accelerated to just 12 months. After all, speed is of the essence in keeping pathogens at bay and preventing significant economic losses.

“By the time you spot the symptoms and see the genetic sequence, it might be too late. The disease has already progressed quite far and the pathogen may have infected other fish as well,” noted Seng.

Because disease spread is heavily intertwined with the environment, effective vaccination also needs to go hand-in-hand with better fishery management. Seng’s visits to fish farms have also shed light on the aquaculture industry’s current practices.

“Some common fishery practices actually multiply the pathogens in the farm,” he explained. “For example, dead [and infected] fish are chopped up into tiny pieces and fed to other fish.”

Climate change is also making the matters worse by warming the Asian waters, which help bacteria thrive and infect fish more readily. Securing the future of Asia’s fishery industry urgently requires several custom vaccines, Seng stressed.

From vaccines to diagnostic tools, combining technological innovation with education initiatives may be the key to building an aquaculture industry that is safe and sustainable—satisfying Asia’s unabating appetite for seafood.

“A very good management system is needed to make sure every fish receives the vaccine and to conduct follow-ups,” Seng emphasized. “Eradication of diseases may not be possible, but through vaccination, we can maximize fishery productivity by minimizing losses from controllable diseases.”