Category Archives: Biology & Life History

Scientists identify tilapia lake virus in Egypt

A new virus that has decimated tilapia populations in Ecuador and Israel has now been found in Egypt according to a new report from WorldFish in partnership with the University of Stirling, Scotland. 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 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, WorldFish: “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.

About WorldFish
WorldFish is an international, nonprofit research organization that harnesses the potential of fisheries and aquaculture to reduce hunger and poverty. Globally, more than one billion poor people obtain most of their animal protein from fish and 800 million depend on fisheries and aquaculture for their livelihoods. WorldFish is a member of CGIAR, a global research partnership for a food-secure future.

About CGIAR
CGIAR is a global research partnership for a food-secure future. Its science is carried out by the 15 research Centers that are members of the CGIAR Consortium in collaboration with hundreds of partners.

University of Stirling
The University of Stirling is ranked fifth in Scotland and 40th in the UK for research intensity in the 2014 Research Excellence Framework. Stirling is committed to providing education with a purpose and carrying out research which has a positive impact on communities across the globe – addressing real issues, providing solutions and helping to shape society.

Scientists net virus behind tilapia die-offs in Israel and Ecuador

An international scientific team led by researchers at Columbia University’s Mailman School of Public Health and Tel Aviv University has identified and characterized a novel virus behind massive die-offs of farmed tilapia in Israel and Ecuador, which threatens the $7.5 billion global tilapia industry. A paper in the journal mBio describes tilapia lake virus (TiLV) and provides information needed to fight the outbreak.

Known in its native Middle East as St. Peter’s fish and thought to be the biblical fish that fed multitudes, tilapia provides inexpensive dietary protein. The world’s second most farmed fish, tilapia is also the basis of aquaculture employment in developing countries in Asia, Latin America, and the Middle East. (The United States is the leading tilapia importer globally.) Since 2009, Israel has seen precipitous declines in tilapia, with annual yields plummeting as much as 85 percent–highly unusual considering the fish is known to be relatively resistant to viral infections. Similar die-offs have been seen in Ecuador and Colombia.

Diseased tilapia

Tilapia diseased from tilapia lake virus infection, Ecuador. Photo: Hugh Ferguson.

The scientists used high-throughput sequencing to determine the genetic code of the virus from tissue taken from diseased fish in Israel and Ecuador. This process would normally be sufficient to identify the culprit, but in this case, the resulting DNA sequences didn’t match any known virus, with the exception of a small genetic segment, that only remotely resembled a virus associated with the reproduction of influenza C.

Undeterred, the researchers employed other tools from their scientific tackle box, providing ample evidence that the genetic material was the same as the implicated virus dubbed TiLV. They used mass spectroscopy to characterize the proteins in cells growing the virus, which matched those they expected to see based on the genetic sequence. By analyzing the structure of viral DNA, they went on to observe 10 gene clusters with complementary endpoints, suggesting a circular form associated with a common type of viral reproduction involving a protein called a polymerase.

Finally and conclusively, healthy fish were exposed to TiLV cultured in a laboratory, resulting in disease that matched with what was seen in those countries: in Israel, the fish had swollen brains; in Ecuador, liver disease. In the coming weeks, the researchers will publish on the link between the TiLV and an outbreak of disease among tilapia in Colombia.

“The TiLV sequence has only minimal similarity in a small region of its genome to other viruses; thus, the methods we typically use to identify and characterize viruses through sequencing alone were insufficient,” says first author Eran Bacharach, a molecular virologist at Tel Aviv University.

“It appears to be most closely related to a family of influenza viruses called orthomyxoviruses; however, we still don’t understand much about its biology,” adds Nischay Mishra, associate research scientist at the Center for Infection and Immunity at Columbia’s Mailman School.

Importantly, the findings provide the genomic and protein sequences necessary for TiLV detection, containment, and vaccine development.

“We are shifting our focus now to implementing diagnostic tests for containment of infection and to developing vaccines to prevent disease,” says Avi Eldar of the Kimron Veterinary Institute in Bet Dagan, Israel.

The team of 18 researchers represent five institutions in four countries: the Center for Infection and Immunity and the New York Genome Center in the U.S., Tel Aviv University and Kimron Veterinary Institute in Israel; the University of Edinburgh, Scotland; and St. George’s University, Grenada, West Indies.

“The New York Genome Center was excited to join in characterizing this novel virus and contribute to this important environmental and globally impactful research,” says Toby Bloom, the Center’s deputy scientific director.

“Gumshoe epidemiology, molecular gymnastics and classical microbiological methods were required to link this new virus to disease,” says Ian Lipkin, senior author, director of the Center for Infection and Immunity and John Snow Professor of Epidemiology at the Mailman School. “Resolution of this mystery was only possible through the concerted efforts of this talented group of international collaborators.”

While best known for identifying viruses behind human disease, the Center for Infection and Immunity, pinpointed the virus beyond a disease that decimated salmon farms in Europe in 2010. They have done similar work with seals, sea lions, and Great Apes.

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The current research was supported by grants from the United States-Israel Bi-National Agricultural Research & Development Fund (BARD IS-4583-13), the Israel Ministry of Agriculture & Rural Development Chief Scientist Office (847-0389-14), U.S. National Institutes for Health (AI109761), USAID PREDICT, and a fellowship to J.E.K.T. from the Manna Center Program in Food Safety and Security at Tel Aviv University. The authors declare no conflicts.

CTSA 2016 Priority – Tilapia Farming Development

Tilapia has been identified as one of the most desired species for aquaculture farming throughout the Center for Tropical and Subtropical Aquaculture (CTSA) region. Although most farming technology is available, the development and expansion of tilapia farming still faces regional challenges. One of the highest priorities in recent years has been stock improvement, and much work has been done in that area. CTSA encourages studies to continue improving the productivity of tilapia farming, and has identified the following top priorities for FY2016:

1) Develop protocols to ensure the quality of the final products.

2) Improve regional access to disease-free tilapia with high-quality genetic traits.

Center for Tropical and Subtropical Aquaculture
41-202 Kalaniana’ole Highway
Waimanalo, HI 96795

Additional Resources:

Does selection in a challenging environment produce Nile tilapia genotypes that can thrive in a range of production systems?

Authors: Ngo Phu Thoa, Nguyen Huu Ninh, Wayne Knibb & Nguyen Hong Nguyen

Abstract

This study assessed whether selection for high growth in a challenging environment of medium salinity produces tilapia genotypes that perform well across different production environments. We estimated the genetic correlations between trait expressions in saline and freshwater using a strain of Nile tilapia selected for fast growth under salinity water of 15–20 ppt. We also estimated the heritability and genetic correlations for new traits of commercial importance (sexual maturity, feed conversion ratio, deformity and gill condition) in a full pedigree comprising 36,145 fish. The genetic correlations for the novel characters between the two environments were 0.78–0.99, suggesting that the effect of genotype by environment interaction was not biologically important. Across the environments, the heritability for body weight was moderate to high (0.32–0.62), indicating that this population will continue responding to future selection. The estimates of heritability for sexual maturity and survival were low but significant. The additive genetic components also exist for FCR, gill condition and deformity. Genetic correlations of harvest body weight with sexual maturity were positive and those between harvest body weight with FCR were negative. Our results indicate that the genetic line selected under a moderate saline water environment can be cultured successfully in freshwater systems.

See full article

Scientific Reports 6, Article number: 21486 (2016)
doi:10.1038/srep21486

This work is licensed under a Creative Commons Attribution 4.0 International License.

 

How to Sex Tilapia

Fish in general are difficult to sex and distinguishing male from female tilapia can be a challenge. Tilapia grown in pond culture can have a problem with excess reproduction. This can lead to stunted growth and lower production rates.

To prevent this problem, farmers can use monosex culture by separating the males from females. Typically, males are preferrred because they grow to a larger size and have greater profit potential.

You can look for physical differences between the sexes. The following description is from Tilapia: Life History and Biology by Thomas Popma and Michael Masser:

“The sex of a 1-ounce (25-gram) tilapia fingerling can be determined by examining the genital papilla located immediately behind the anus (Fig. 1). In males the genital papilla has only one opening (the urinary pore of the ureter) through which both milt and urine pass. In females the eggs exit through a separate oviduct and only urine passes through the urinary pore. Placing a drop of dye (methylene blue or food coloring) on the genital region helps to highlight the papilla and its openings.”

Fins and genital papilla of the Nile Tilapia.

Fins and genital papilla of the Nile Tilapia. (Credit: Tilapia: Life History and Biology by Thomas Popma and Michael Masser)

 

 

 

 

 

 

 

 

 

The following picture gives you a reference for differentiating the sex of tilapia.

Male and female tilapia are determined by viewing the genital papilla. The tilapia on the left is a male and on the right is a female tilapia. (Credit: Fish and Allied Aquaculture, Auburn Univ.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Home growers can use tilapia behavior to help sex their tilapia. Put a small number of tilapia in an aquarium along with some gravel. The male will typically dig a nest and defend it. Females will tend to hide unless they are spawning. You can remove males that display nesting behavior one by one and move them to separate containers. When the remaining fish no longer show nesting behavior, then you can assume they are all females. You can add one of the males back into the aquarium and start a breeding colony.

How to identify gender in tilapia