Can Bacteriophages Improve the Welfare of Farmed Fish? Early Evidence from African Catfish Aquaculture study

By Nnaemeka Emmanuel Nnadi @ 2026-08-08T08:37 (+20)

Nigeria is the largest aquaculture producer in Sub-Saharan Africa and the second-largest on the continent behind Egypt. Nigeria has a total domestic output across both wild capture and aquaculture of about 1.4 million metric tons. Nigeria's fishery sector is one of the biggest untapped economic opportunities in Africa. 

Disease outbreaks in aquaculture are a very big indicator of poor fish welfare. In aquaculture, diseases rarely happen in a vacuum; a myriad of factors contribute to this, and they include poor water quality, overcrowding, and chronic stress. One of the pathogens we are studying is Aeromonas hydrophila, which can cause serious disease and mortality in farmed fish. It is responsible for Motile Aeromonas Septicemia (MAS), commonly known as hemorrhagic septicemia or red sore disease

The conventional response is often antibiotics. But this creates another problem: Antibiotic use and chemical pollution create serious risks for food safety and nature. Some of the major problems with the use of antibiotics in fish farming are:

• Drug Residues: People eat leftover medicine when they consume contaminated fish.
• Superbugs: Low levels of drugs in water help harmful bacteria build resistance to medicines.
• Fish Health: Chemicals cause organ damage, stress, and poor growth in aquatic life.
• Mixed Pollution: Heavy metals or plastics in the water can make the toxic effects of drugs worse.

We set out to answer the question: Can bacteriophages reduce disease-related suffering in farmed fish while reducing reliance on antibiotics?

Will phage therapy use encourage farmed fish? 

This, I think, is an important question, since the goal of animal welfare is to do as much as possible while at the same time improving the welfare of farmed animals. Whether phage therapy increases fish farming depends on how it is used and what effect it has on the industry. 

There are three possible scenarios:

1. The expansion effect (possible concern): In this case, phage therapy significantly lowers production costs and increases profitability, thereby encouraging expansion of aquaculture, leading to more fish being farmed.
2. Welfare improvement without expansion (most desirable): In this case, phage therapy primarily replaces antibiotics and improves health in existing farms, thereby leading to reduced disease, pain, and mortality among fish that are already being farmed without substantially increasing production. This would represent a clearer animal welfare gain.
3. Transition to higher-welfare farming: In this case, phage therapy leads to better disease control and is tied to welfare standards or antibiotic stewardship programs, encouraging farmers to improve husbandry rather than simply increase stocking density. In this case, phage therapy becomes one component of a broader welfare-focused management strategy

Methods

This research was conducted at the Centre for Phage Biology and Therapeutics, Jos, Plateau State, Nigeria. Phages for Aeromonas hydrophila were isolated from fish ponds using standard protocols. We conducted a controlled laboratory study to evaluate whether bacteriophage therapy could reduce Aeromonas hydrophila-induced disease in African catfish (Clarias gariepinus). Fish were experimentally infected with A. hydrophila and assigned to treatment and control groups. The treatment group received a bacteriophage preparation targeting A. hydrophila, while the infected control group did not receive phage treatment. Fish were monitored throughout the experiment for survival, disease progression, bacterial burden, and evidence of disease transmission. The study was designed as a proof-of-concept to assess the potential of bacteriophage therapy as a disease-control strategy and its implications for improving the welfare of farmed fish while reducing reliance on antibiotics

Early results

The results from our initial laboratory experiment are encouraging, although they should be interpreted as preliminary.

Fish treated with bacteriophages showed 100% survival, compared with approximately 40% survival in the infected untreated control group. We also observed lower bacterial loads and reduced disease spread in the phage-treated fish.

Conclusion

These preliminary findings suggest that bacteriophage therapy may represent more than an alternative to antibiotics. It may offer a practical way to reduce disease-related suffering in farmed fish, one of the largest and arguably most neglected populations in animal agriculture.

This is an initial proof of concept and requires replication, larger trials, and field validation. Phage therapy could become an important addition to the portfolio of interventions aimed at reducing suffering in animals that already exist within food production systems.

Call to action

I would welcome feedback from the Effective Altruism community on three questions:

1. How should the potential welfare benefits of phage therapy be weighed against the possibility that more effective disease control could indirectly support expansion of aquaculture?
2. If this work continues to produce encouraging results, what evidence would you want to see before considering it a promising, scalable intervention for improving fish welfare?