Scientists are now trying to establish a firm link between the virus and a recent surge in mortalities in Egyptian farmed tilapia.
Tilapia Lake Virus (TiLV) is a global threat to the tilapia farming industry, which is worth US$7.5bn per year.
In recent years, fish farms in Egypt have seen increased mortality of farmed tilapia in the summer months, so-called “summer mortality”. Epidemiological surveys indicated that 37% of fish farms were affected in 2015 with an average mortality rate of 9.2% and an estimated economic impact of around US$100 million/year.
Identifying the cause of and preventing these fish deaths is of significant importance in Egypt, which relies on domestic aquaculture for 60% of fish consumed with tilapia making up 75% of that production. Tilapia is the cheapest form of animal protein in the country, so the findings have significant implications for the Egyptian people, particularly poorer consumers. The Egyptian aquaculture sector is the largest producer of farmed fish in Africa (1.17 million tonnes in 2015) and the third largest global producer of farmed tilapia after China and Indonesia.
Tissue samples from seven farms affected by ‘summer mortality’ were tested at the University of Stirling’s Institute of Aquaculture for TiLV with three of the seven samples testing positive.
Dr Michael Phillips, Director of Science and Aquaculture, at WorldFish said: “Tilapia were previously considered to have good disease resistance. While the report and the emergence of TiLV will likely not dent the species’ significance in global aquaculture it is a sign that greater efforts must be made to manage disease risks in tilapia farming. Research now needs to focus on finding solutions for this emerging challenge to the world’s tilapia farms.”
“Globally, there is no aquaculture system that is free from the risk of disease,” explains virologist Professor Manfred Weidmann from the University of Stirling. “Unless we are able to manage disease, minimize its impact, and bring down the prevalence and incidence of diseases we will not be able to meet future demand for fish.”
WorldFish scientists, in collaboration with the University of Stirling, will now work to establish whether TiLV is the primary cause of ‘summer mortality’ and, if that is the case, recommend rapid action to control the spread of the disease, including increased biosecurity in the short term. Longer-term strategies being studied by WorldFish and partners include vaccines and the genetics of disease resistance, that may open the way towards breeding of strains of tilapia that are resilient to TiLV.
Tilapia is an important species for aquaculture because it can be grown in diverse farming systems and is omnivorous, requiring minimal fishmeal in its feed. It has a naturally high tolerance to variable water quality and can grow in both freshwater and brackishwater environments. Tilapia are particularly important in developing world contexts where they are inexpensive and easy for small-scale farmers to grow for food, nutrition and income.