Fish zoonoses remain an underestimated risk as aquaculture and raw-fish consumption expand

Fish and aquatic environments are still frequently overlooked in zoonotic-disease surveillance, despite the rapid growth of aquaculture, international seafood trade and consumption of raw or lightly processed fish. A new review highlights a diverse spectrum of bacterial, parasitic and environmental hazards and argues for closer integration of aquatic animal health, food safety and human-health surveillance.

Historically, fish have been considered a relatively minor source of zoonotic disease compared with terrestrial livestock. The authors argue that this perception may partly reflect underdiagnosis and limited surveillance, while expanding aquaculture, seafood trade, raw-fish diets and ornamental-fish ownership are creating more opportunities for human exposure.

Bacteria and parasites dominate the risk

Among fish-associated zoonotic agents, bacteria remain particularly important. The review identifies Mycobacterium spp., Streptococcus iniae, Clostridium botulinum and Vibrio vulnificus among organisms with strong evidence for genuine fish-to-human transmission, while several additional bacteria are associated with fish handling or consumption.

Parasites constitute another major group. Nematodes, cestodes and trematodes can be transmitted through raw, undercooked or inadequately preserved fish, making changes in culinary habits relevant to zoonotic exposure.

The review's outbreak table illustrates the diversity of documented events, including gnathostomiasis associated with fish consumption in Mexico, botulism linked to fish in Norway and Germany, Salmonella associated with smoked salmon in the Netherlands, listeriosis linked to smoked fish and severe Streptococcus agalactiae ST283 infections following consumption of raw freshwater fish in Singapore.

Few true fish viruses infect humans

The viral picture is different. The authors stress that few viruses infecting fish are confirmed zoonoses. Much of the viral risk associated with seafood instead comes from contamination of aquatic products or harvesting waters with human pathogens such as norovirus and hepatitis A virus.

In other words, seafood can act as a vehicle without the fish necessarily serving as the biological reservoir of the virus. That distinction is important for surveillance because the control measures are very different: environmental sanitation and food hygiene become more important than controlling infection within the fish population itself.

Infection is not limited to eating fish

Consumption is only one route of exposure. The review describes infection through raw or undercooked fish, damaged skin during handling, contaminated aquarium or farm water and, more rarely, aerosols or vectors. It estimates that about 46% of fish-associated zoonoses involve oral transmission, while waterborne exposure and skin contact also make substantial contributions.

That places several occupational groups at particular risk, including aquaculture workers, fish processors, anglers, aquarists and veterinary or laboratory personnel. People who are immunocompromised or have chronic underlying disease may also be more susceptible to severe infection.

Contact zoonoses are particularly relevant for organisms such as Mycobacterium marinum and Vibrio vulnificus, where minor cuts or abrasions can provide an entry point during fish handling or aquarium maintenance.

Aquaculture also raises an AMR issue

The review connects fish zoonoses with another major One Health concern: antimicrobial resistance. Antimicrobials administered in aquaculture can enter surrounding aquatic environments, potentially selecting resistant organisms. The authors specifically highlight resistance risks involving bacteria such as Aeromonas hydrophila, Streptococcus iniae and Vibrio spp., and advocate prudent antimicrobial use, vaccination where available and improved husbandry.

This makes aquatic animal health relevant not only to foodborne disease but also to environmental AMR surveillance.

Cooking remains the simplest protection

Many preventive measures are well established. Adequate cooking remains the most reliable method for eliminating most parasites and bacterial pathogens. For fish intended to be eaten raw, freezing is particularly important against anisakid parasites. The review cites US guidance recommending −20°C for at least seven days or −35°C for at least 15 hours, although freezing does not eliminate heat-stable Anisakis allergens.

At farm level, better water quality, lower stocking pressure, routine pathogen surveillance and responsible antimicrobial use can reduce pathogen burden before fish reach consumers.

For people handling fish, waterproof gloves, wound protection and immediate hand washing remain simple but important measures.

Aquatic animal health deserves a larger place in One Health

The underlying message of the review is that fish zoonoses importance may be systematically underestimated.

Aquaculture production and seafood trade continue to expand, while consumer demand for sushi, sashimi, ceviche and other minimally processed products increases opportunities for exposure. At the same time, ornamental fish and home aquaria create direct-contact pathways that are largely absent from conventional food-safety surveillance.

The authors therefore call for coordinated monitoring involving veterinary services, public-health authorities, food-safety regulators and the aquaculture industry.

Aquatic ecosystems should no longer be treated as peripheral to zoonotic-disease surveillance. Fish, water, food production and human exposure form a connected epidemiological system, and surveillance needs to reflect that reality.