How fish farmers can overcome disease burden in ponds

Among the many diseases that affect fish in ponds, Aeromonas hydrophila stands out as the most common bacterial infection encountered by Ugandan fish farmers, especially those rearing tilapia. Recent data shows that this pathogen has a 43.8 percent prevalence rate along the Lake Victoria Basin. Other harmful bacteria often found in conjunction with it include Aeromonas sobria, Edwardsiella tarda, Flavobacterium species, and Streptococcus species. Infected fish typically exhibit symptoms such as skin ulcers with reddish rims, fin rot, loss of appetite, bulging eyes, swollen abdomens, and abnormal swimming behavior. In severe cases, the infection causes skin to peel off, leading to death if left untreated.

Aquaculture disease management

Dr Gillian Taylor from the National Academy of Medicine in Canada emphasised the importance of two main approaches to disease management in aquaculture systems. The first is therapeutic treatment, which includes the use of antibiotics, antimicrobials, and chemotherapeutic agents. While these are effective in treating active infections, their overuse has led to the growing threat of antimicrobial resistance (AMR), a global health concern. The second and increasingly preferred method is prophylaxis—preventive care that includes vaccination, immunostimulants, probiotics, and improved farm management practices.

These measures aim to reduce the load of disease-causing pathogens and prevent outbreaks before they occur. Dr Taylor cautioned that, if left unaddressed, antimicrobial resistance could lead to 10 million annual deaths in animals and fish by 2050. She urged farmers to improve pond hygiene and water quality and to consult qualified professionals before administering medication to their stock.

Local innovation

In Uganda, researchers from Makerere University’s College of Veterinary Medicine, Animal Resources and Biosecurity (COVAB), led by Dr Andrew Tamale, are developing a promising solution in the form of bacteriophages—viruses that infect and kill bacteria. In their experiments, the team introduced phages into ponds where Aeromonas bacteria were present. The trials, conducted in selected fish farms in Wakiso, Nakasongola, and northern Uganda, produced remarkable results. Under ideal conditions—water temperature between 27 and 28 degrees Celsius, a pH of 6.5 to 7.5, and healthy, bacteria-free fingerlings—the phages multiplied naturally and significantly reduced the bacterial load. 

This biological method offers a sustainable alternative to antibiotics. The solution, available in liquid form, is applied in doses ranging from 0.1 to 100 millimeters, depending on severity. Farmers are encouraged to consult veterinarians for proper administration. The research was conducted under a four-year project, which has since concluded, and the team is now focused on farmer sensitisation and scaling up the availability of phages through university distribution channels.

Other common diseases

Apart from bacterial infections, fish are also vulnerable to fungal and parasitic diseases. Fungal infections usually manifest as cotton-like growths on the fish’s body, fins, or mouth. Parasitic infections often cause symptoms such as listlessness, clamped fins, and scraping against surfaces. These conditions are typically treated with antifungal or antiparasitic medications, salt baths, and improved water hygiene. Swim bladder disease is another common issue, especially in poorly maintained systems. Affected fish may float uncontrollably or swim in awkward patterns. Treatment often involves antibiotics, water quality improvements, and feeding vitamin-enriched diets. Ich, or white spot disease, is identifiable by tiny white cysts on the fish’s skin and fins and is treatable with commercial medications like Ich-X. Across all diseases, early detection remains key, along with adherence to proper treatment guidelines and avoidance of overmedication.

A growing sector facing big challenges

According to a 2020 report by the Food and Agriculture Organisation (FAO), global aquaculture production reached 122.6 million tonnes, valued at $281.5 billion. Of this, aquatic animals made up 87.5 million tonnes, while algae accounted for 35.1 million tonnes. Though most growth was driven by countries such as Chile, China, and Norway, Africa experienced mixed results. While Egypt and Nigeria saw declines, other African nations recorded a 14.5 percent increase in production from the previous year. Asia continues to dominate, producing 91.6 percent of the world's aquaculture output. However, as the sector grows, concerns over environmental sustainability and disease management persist. The FAO stresses the importance of responsible practices to ensure long-term viability and food security.

Looking ahead

The road to sustainable aquaculture lies in science-driven solutions and farmer education. From vaccine development to bacteriophage therapy and improved husbandry, multiple strategies are being pursued to reduce fish mortality and combat disease outbreaks. Farmers must adopt these innovations while working closely with scientists and veterinary experts. With rising global demand for fish and a warming planet challenging aquatic ecosystems, proactive disease management is not just a necessity—it is the foundation of a resilient and productive aquaculture industry.