Fish Biosecurity in a Warmer Climate

Prevention First… Always

Warmer weather can bring real pressure to fisheries, hatcheries and aquaculture sites. As water temperature rises, fish can become stressed, dissolved oxygen can fall, and conditions may become more favourable for certain bacteria, viruses and parasites. Disease outbreaks including streptococcosis and edwardsiellosis are often associated with higher temperatures, while infected aquatic animals have also been shown to experience higher mortality in warmer conditions. Reference: https://www.nature.com/articles/s41467-020-15735-6

Antibiotics may have a place in veterinary-led treatment for a diagnosed bacterial infection, but they are not a catch-all answer. They will not treat viral or parasitic disease and relying on them after problems appear can mean the site is already dealing with stock losses, disruption and a larger pathogen burden. Good biosecurity helps reduce the chance of reaching that point in the first place.

Why warmer conditions raise disease risk

Temperature is only one piece of the picture, but it can magnify several familiar risks. Some disease-causing organisms reproduce, survive or spread more effectively within warmer temperature ranges and warm water naturally holds less dissolved oxygen. This can stress fish, reduce feeding performance and weaken their ability to cope with infection. Notably, higher feeding rates, increased waste and algal growth can also add pressure to water quality, particularly where water exchange or filtration is limited.

In environments where frequent handling, grading, transport takes place, sudden temperature swings can easily occur, and this can be particularly problematic during hot conditions and especially so even in temporarily crowded holding tanks. These frequent activities introduce a number of new aquatic biosecurity risks. Nets, boots, equipment, vehicles, staff and fish movements themselves have the potential to carry pathogens between ponds, tanks, raceways or sites.

And the risks aren’t limited to those created by human interventions; birds, pests and visiting animals may move contaminated water, organic material or infected fish between locations and this happens more often when wildlife is forced to move between ever more scarce water sources.

On the flip side, climate change doesn’t just mean warmer, drier weather. The likelihood of extreme meteorological events such as unseasonal heavy rainfall, flooding, and warmer source water can interfere with water quality, introducing contamination risks.

Climate-related changes can shift the balance between fish and pathogens, potentially changing the frequency and distribution of disease. UK research has highlighted that warmer water and extreme weather may raise susceptibility to disease in both wild and farmed salmonids. https://pubmed.ncbi.nlm.nih.gov/20561287/

Why prevention matters

A treatment-first approach can be costly. By the time clinical signs of disease are visible, a pathogen may already be established in the stock, water and any surrounding equipment. Antibiotics can be effective where a susceptible bacterial infection has been correctly diagnosed and treatment is prescribed under appropriate veterinary direction. Inappropriate and unnecessary antibiotic use has been proven to add to antimicrobial-resistance concerns.

A prevention-led biosecurity plan gives fisheries more control. It focuses on reducing the chance of pathogens entering the site, limiting their movement if they do enter, and spotting warning signs before an issue becomes a full outbreak. Current guidance for aquaculture places particular emphasis on known health status for incoming stock, quarantine, biosecure transport, hygiene for people and equipment, separation of production groups, regular health monitoring and effective waste management. https://aac-europe.org/wp-content/uploads/2024/12/AAC-Report-Fish-Health-Management-2024.pdf

Practical warm-weather biosecurity measures

During warmer periods, it is extremely important to review biosecurity routines rather than simply carrying on with a ‘year-round’ plan.

-          Monitor water temperature, dissolved oxygen, ammonia, nitrite, pH and clarity more frequently, particularly early in the morning when oxygen can be lowest.

-          Avoid unnecessary handling, grading and transport during the hottest part of the day.

-          Keep stocking densities sensible for the site, species and available oxygen.

-          Isolate and observe new or returning fish before they join established stock.

-          Use dedicated equipment for separate units wherever possible. Colour-coded nets, buckets and boots make this easier to manage.

-          Clean away visible organic matter before disinfection, as dirt and biofilm can reduce the effectiveness of hygiene measures.

-          Maintain controlled entry points and clear visitor rules, including footwear and equipment protocols.

-          Record mortalities, behaviour changes, appetite, lesions and water-quality readings. Patterns often appear in the records before a problem becomes obvious on the bank.

-          Have a written response plan: who to contact, how to isolate a unit, and how to stop equipment moving around the site.

Using Virkon® AQUATIC as part of prevention

Disinfection is an important part of a wider biosecurity programme.

Virkon® AQUATIC has been specifically developed for aquaculture biosecurity and is designed to support pathogen control across fish and shrimp production environments. LANXESS identifies applications including surfaces, equipment, footwear and other key biosecurity points within aquaculture operations.

The important point is that disinfection works best as part of a consistent preventative programme rather than simply being introduced once disease has become established.

Used correctly and in accordance with the current product label and technical guidance, Virkon® AQUATIC can support hygiene protocols around equipment such as nets, boots and handling equipment, production areas, transport equipment and controlled entry points.

Application rates, contact times and approved uses should always follow the current product label and relevant local regulatory requirements.

Use biocides safely. Always read the label and product information before use. Approved applications and uses may vary by country.

A Prevention-First Approach

Warmer conditions can increase the pressure placed on fish health and biosecurity, but disease outbreaks should never simply be regarded as inevitable.

Good water management, reduced stress, careful stock movements, quarantine, early observation and consistent cleaning and disinfection all help reduce the opportunities for pathogens to enter, establish and spread.

For fisheries, hatcheries and aquaculture operations looking to strengthen their biosecurity programme, Day-Impex can provide specialist product support and guidance across the Virkon® AQUATIC range.

Prevention first. Stronger biosecurity. Healthier stock.

Contact the Day-Impex team to discuss your requirements.