ICAR-Central Institute of Brackishwater Aquaculture, Chennai; CSIR-Institute of Genomics and Integrative Biology, new Delhi; Temasek Lifesciences Laboratory, Singapore
The Asian seabass, commonly known as bhetki in West Bengal, koduva in Tamil Nadu and narimeen in Kerala, is a hugely popular edible fish in India. The species is also found in southeast Asia and Australia. Every year, nearly 1,000 tonnes of seabass is consumed in the country. The fish, caught from the sea, generally is the range of1 and 5 kg, whereas those in culture farms weigh between 0.5 and 1.6 kg during a culture period of 6- 10 months.
Considering the popularity of the fish, there has been an ongoing effort to increase its production in the farm. However, there have been two main difficulties: induced maturation and breeding of the fish in captivity, and larval rearing using desired live and formulated feeds. It is very tough to mature marine fish in captivity because of difficulties in controlling the abiotic factors like salinity, temperature and hormonal levels.
The first of these difficulties was overcome in 1997, when after a decade-long effort at ICAR-Central Institute of Brackishwater Aquaculture, or CIBA, we were able to standardise the conditions for broodstock development and breeding seabass in a controlled environment. Over the years, we have improvised these conditions and helped several farmers by producing and supplying seed to culture this fish in their farms.
We realised that the solution to the second problem, relating to body weight, lay in initiating a study to unravel the difference among the fish at different locations. As some of these fish do grow up to about 3 kg, we know that the other fish also had the genetic potential to grow faster and larger. We needed to start a selective breeding programme to ensure superior progeny.
As a first step towards genetic improvement, we needed to map the genetic makeup of the species to know whether the fish in different regions are different or not. We collected samples of the species from the west, east coast of India, and Andamans, and compared them to those from Australia and southeast Asian countries. The study revealed that that the Asian seabass in India is very much distinct from that of the southeast Asian region and also Australia. The present project has unravelled a lot of information on the genetic makeup of these fish. The information flowing from this project will be helpful in initiating a selective breeding programme.
A selective breeding programme involves improvement of a desirable character like, for example, an increased growth rate and resistance to diseases. There is no introduction of any new genes, but only consolidating desirable genes in a fish.
Asian seabass is the first marine fish in India whose genetic map has been prepared. The genetic map of the freshwater fish rohu is already available and that of katla is being dealt with at other fisheries institutes of the Indian Council of Agricultural Research.
