Tilapia, a model fish for research and genome frequencing

Tilapia, a fish that originates from southern countries, has been introduced in over 100 countries. It is the second most commonly produced fish in aquaculture in the world after carp (99 per cent is produced and consumed in China).

Raising tilapia is easy and inexpensive. It adapts well to fresh or salt water and fattens fast. Unlike most salmoniforms in aquaculture (salmon, trout, perch, bream), for which fishmeal and fish oil constitute an essential part of their diet, tilapia is lower down in the trophic or food chain and feeds on algae, plankton or small animals. In extensive and semi-extensive production systems, tilapia is largely fed on vegetable waste (rice, cotton, etc.).

Thus, with output exceeding 2 million tons each year, tilapia production contributes to sustainable development without damaging marine resources. This is one of the arguments put forward to support research into the complete sequencing of the tilapia genome. In addition, it is one of two species of interest to aquaculture which is being studied more than any other in laboratories.

Sex determination at the service of aquaculture

This model fish belongs to the order percomorphs which includes many French and European species, such as perch, bream and pargo bream. These fish take a long time to reach sexual maturity, which means that their genetic study is not easy. As tilapia has a short generation gap, it can be used as a study model for improving percomorphs. It is also the main group used for studying the phenomena of speciation (birth of a new species).

Of the 10 laboratories involved in the tilapia genome sequencing project, CIRAD and Stirling University of Aquaculture (Great Britain), are particularly interested in the benefits that the project may represent for aquaculture. They are researching genes linked to characteristics of interest, such as growth, rusticity, sex ratio (proportion of males to females), etc.

The tilapia breeders are calling on research for the selection of male tilapias, which grow much faster than the females. The CIRAD research unit Aquaculture and aquatic resource management is developing research programmes to find a real hormone-free alternative for producing single sex male populations. Research into genetics and the use of breeding conditions could provide solutions to the danger of hormones in food, human health and the preservation of biodiversity.

”High water temperature may influence the sex of fingerlings, so we are genetically selecting parents in the hope that the progeny will have this heritable characteristic, “ explains Jean-François Baroiller, a scientist at the research unit Aquaculture and aquatic resource management. Genetic markers for thermal sensitivity are used to optimise this kind of selection and also to study individuals of interest within the natural diversity of tilapias. A similar approach has been set up to develop tilapias resistant to high variations in water salinity in order to meet the demand of numerous producing countries.

The expected development of the first sequences will complete numerous specific genome resources for tilapia that have already been developed by CIRAD. Three PhD students from the research unit Aquaculture and aquatic resource management are working full-time on these issues in collaboration with international research organisations. The sequencing project is already of considerable benefit to the scientific community as well as for world aquaculture.

^{* CIRAD (France)
University of Maryland (United States)
Stanford University (United States)
Rutgers University (United States)
Harvard University (United States)
University of Konstanz (Germany)
Tokyo Institute of Technology (Japan)
University of Stirling (Scotland)
University of Bern (Switzerland)
Georgia Institute of Technology (United States)}

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Tilapia, a model fish for research and genome frequencing