Introduction
Infectious Spleen and Kidney Necrosis Virus (ISKNV) has become a significant threat to tilapia farming, particularly in Ghana. Since its discovery in Lake Volta in 2018, the virus has caused devastating fish mortality rates, with losses as high as 90%, with losses exceeding 10 tonnes of
fish per day. Research indicates that 80% of farms have reported average daily mortality rates of 40%, underscoring the virus’s widespread impact. The severity of the virus occurs across different life stage, with the effect becoming more pronounced as the fish grow and their immune systems develop. This write-up outlines the impact of ISKNV on tilapia, its transmission, and effective prevention and management strategies to protect your farm.
What is ISKNV?
ISKNV is a viral disease affecting tilapia, causing high mortality rates, particularly in the nursery stage of their development. The virus attacks the spleen and kidneys, leading to impaired immune function and increased susceptibility to secondary infections. ISKNV was first detected in Lake Volta in September 2018 (Ghana Fisheries Research Division, 2018). Since then, the virus has become endemic across tilapia farms, particularly in the Lake Volta region
Impact on Tilapia Farming
The virus has a significant impact across various life stages of tilapia, but the severity is most pronounced during the nursery stage (1-10g). Here, mortality rates can reach as high as 60-90%, causing economic losses for farmers.
- Hatchery Stage (0-1g): At this early stage, ISKNV tends to have a moderate impact. Infected fry may show lethargy, abnormal swimming, and darkened bodies, but mortality is usually not as severe as during the nursery phase.
- Nursery Stage (1-10g): The virus becomes highly impactful at this stage. Fish often develop swollen abdomens and lesions, exhibit impaired swimming, and suffer from secondary infections due to weakened immune systems. The impact increases with stocking density and poor water quality (Jansen et al., 2021)
How the Virus Spreads
ISKNV spreads rapidly through contaminated water, equipment, and direct contact between fish. Factors such as high stocking densities, poor water quality, and stress increase the likelihood of outbreaks. This makes it crucial to implement measures that control and prevent the spread of the virus (Schenk et al., 2019)
Prevention & Management Strategies
To effectively manage and prevent ISKNV outbreaks, a multifaceted approach is essential. Key strategies include:
- Biosecurity Measures Preventing the introduction and spread of the virus is the first line of defense. Implement strict biosecurity practices, such as:
- Disinfecting tanks, equipment, and water sources.
- Limiting personnel access to the nursery.
- Enforcing hygiene practices among workers to reduce cross-contamination risks.
- Water Quality Management Poor water quality is a major contributing factor to ISKNV outbreaks. Regular monitoring of water conditions such as pH, dissolved oxygen (DO), temperature, and ammonia levels helps maintain an optimal environment that reduces stress in fish. Filtration and UV (Ultraviolet) sterilization can also help remove viral particles from the water (Shamim et al., 2022).
- Stress Reduction Stress is a key factor that worsens the impact of ISKNV. To keep your fish healthy, try to avoid overcrowding, temperature fluctuations, and rough handling, as these stresses can make them more vulnerable to infection. Ensure your tanks and ponds (culturing systems) are of adequate size, with proper water flow.
- Early Detection & Monitoring Early detection is crucial in managing ISKNV. Routine diagnostic tests, such as Polymerase Chain Reaction (PCR) and histopathological exams, are effective in identifying the virus in fish tissues before clinical signs appear. Regular inspections for clinical symptoms of the virus enable timely intervention to prevent outbreaks (Zhang et al., 2023).
Conclusion: Protecting Your Farm from ISKNV
ISKNV is a major challenge for tilapia farming, particularly during the nursery stage, where it can cause high mortality rates. However, by implementing strong biosecurity measures, maintaining water quality, reducing stress, and utilizing early detection techniques, farmers can effectively manage and mitigate the risks associated with this virus. While there is no vaccine for ISKNV, ongoing research into viral control methods remains essential for tilapia farming’s sustainability. Heat treatment has shown potential in reducing ISKNV mortality, but its high energy costs and practical limitations make it unfeasible for many farmers. For those unable to utilize this method, strengthening biosecurity, managing water quality, and reducing stress are crucial. Additionally, natural remedies like boosting fish immunity with Vitamin C and using probiotics to improve gut health and water quality can play an important role in supporting fish health. By combining these strategies, farmers can effectively manage ISKNV and enhance the resilience and profitability of their tilapia farms.
FAQ
Q: Can ISKNV be prevented entirely?
A: While complete prevention may not be possible, following strict biosecurity measures, managing water quality, and reducing stress are the best ways to minimize the risk of outbreaks.
Q: How can I detect ISKNV in my fish before clinical signs appear?
A: Regular PCR testing and histopathological exams are effective in detecting the virus early, allowing for timely intervention.