Human Health Lies in the Fins of Fish

What do bats, dogs, tigers, monkeys, and mink have in common? First of all, they’re mammals. More importantly, they are all able to be infected with and spread the novel SARS-COV-2 virus (COVID 19). Like SARS, Ebola, and Hendra, the COVID pandemic once again demonstrates the link between animal and human health.

As healthcare systems continue to struggle with this pandemic, COVID is merely the most recent reminder that diseases can jump from animals to humans. Farmed fish are no exception to this rule. COVID has also been found in fish.

The health of fish consumers depends on the health of the fish. On farms, fishes’ health is compromised by diseases and stressful practices, such as rough handling, monotonous environments, and crowding. These issues arise because fishes’ well-being is compromised. Ultimately, fish welfare matters to both fish and human health.

Fish Welfare and Food Safety

Germs can jump from animals to humans and vice versa. Common management practices such as handling and crowding regularly cause wounds and lesions on the farmed fish's skin. Bacteria can enter through these wounds and are then ingested by consumers. Once germs enter the fish, they are able to quickly multiply. They do so phenomenally well when fish are stressed because stress compromises their immune system. All of this bacterial activity creates a serious health risk for consumers, a significant concern that has been acknowledged by the European Food Safety Authority.

Stressed fish are also more susceptible to viruses. On farms, most disease outbreaks are linked to poor rearing practices that place stress on fish. The industry typically uses antimicrobials to combat disease outbreaks, but any erroneous administration of antimicrobial agents holds the risk of furthering antimicrobial resistance in both fish and humans.

Worms in Fish?

Disease isn’t the only thing that can be transmitted from fish to humans. In the past, consumers have found nematodes (roundworms) in fish meat. It is hard to prevent parasites such as worms from entering fish, especially when they are given live feed. Instead, it is easier to identify and treat the signs of worm infection. Producers need to monitor fishes’ well-being to identify issues and act accordingly. Again, providing optimal welfare is the key to avoiding such incidents.

Product Quality

Farmers raise most fish to be processed and sold. Thus, an impeccable product is the holy grail of every farmer. Although inhumane rearing and slaughter practices continue to be industry standard, more and more studies suggest that high welfare creates a better product. For example, fish that experience less stress have a later rigor mortis (the process of becoming stiff after death). Preventing stiffness prolongs the fishes’ shelf-life and makes the meat firmer, less watery, and more colorful - all attributes that consumers value in fish meat.

Silver carp with bleeding skin due to inhumane slaughter methods.

Optimal water quality, minimal handling, resting time, and stunning before slaughter make for a fresh, unscathed product.

“What is least traumatic to the animals is best for meat quality” (Flick, David, & Kuhn 2013).

The Power of Play

New research has revealed another surprising element to ensuring food safety and fish welfare: environmental enrichment. Environmental enrichment is the addition of structural, social, dietary, and/or sensory complexity. Enriching fishes’ environment improves the positive welfare of fishes and also positively influences fish growth and health.

Hugh Ross, a salmon farmer from Loch Duart, observed his salmon nipping on each other’s fins. Fin damage lowers the price of fish on the market and seriously stresses the fish. By adding simple structures replicating seaweed, he observed a decrease in fin-nipping. The fish also distributed themselves more evenly across the tank, thus giving each fish more space. Recently, Hugh’s anecdotal findings were backed up by a study that observed fish growing faster when they were given environmental enrichment.

Dusky grouper during an experiment exploring the effectiveness of environmental enrichment for captive fish. Photo credit: IPMA, Olhão Portugal.

A note on environmental enrichment: To date, only limited research on appropriate environmental enrichment for different species is available, and generalizing interventions can be detrimental. For example, added substrate, which improves the welfare of some fish species, can also be a breeding ground for parasites (Gangadhara et al. 2016). While we should use environmental enrichment where it has proved effective, we need more species-specific research to properly utilize this welfare improvement.

Harmful Wastewater

Moving on from artificial to real seaweed, enriching farms with marine fauna is also a great tool for wastewater treatment. Many fishes enjoy the structural complexity of seaweed in their tanks, and these underwater plants oxygenate the water during the day.

Seaweed also removes harmful nutrients from the environment. Fish farms are increasingly critiqued for discharging nutrients into nearby waters. Farm water drainage contains high levels of nutrients that pollute local waterways and deplete their oxygen. Using seaweed as a biofilter can remove a substantial amount of these nutrients (learn more: Schuenhoff et al. 2003, Lamprianidou, Telfer, & Ross 2015). This intervention cleans the fishes’ environment and protects both humans and wildlife in the neighborhood from the adverse impacts of contaminated groundwater. Thus, enriching farms with seaweed can offer a win-win situation for the fish, the environment, and humans.

Ultimately, the welfare of fish strongly relates to the well-being of humans. If we want to protect the environment, our health, the fish, and have a good product, we need to take into account the welfare of fish.