India being an agricultural country, its economy also mainly depends on the successful production of agricultural products. Besides, over 70 percent of Indian population inhabit rural areas. Until 1960s, India was not self-sufficient in producing food grains and had to depend on other countries for filling the gap between inadequacy and self-sufficiency. To overcome this situation and to feed its ever increasing population, the country had to struggle its way to self-sufficiency for producing food grains. To achieve this goal, agriculture scientists in the country were at the task from 1950s and by mid 1970s India could achieve self-sufficiency in producing food grains through developing genetically superior high yielding varieties of wheat and paddy and other vegetable products of the green-revolution. Simultaneously there were also efforts to improve and increase the farm animal products and an appreciable rise in the yield of milk and eggs production has been witnessed since the past one and a half to two decades.
Coming to the fisheries sector, India possesses nearly 11 percent of the world's 20,000 known species of fish, and is one of the richest nations in the world with regard to genetic resources of fishes which are distributed over a network of perennial river systems in the country. With regard to culture fisheries or aquaculture sector, though it appears that fish culture in India is almost as old as in China, the average per hectare production per year remained as low as 0.6 tones until the 1960s. This was due to lack of proper technology and fish farmers that had to follow traditional or empirical methods for their fish farming.
The aquaculture systems in India and its neighbouring countries such as Bangladesh and Pakistan, mainly constitute Indian major carps viz. the Catla (Catla catla, Hamilton), the rohu (Labeo rohita, Hamilton), the mrigal (Cirrhinus mrigala, Hamilton) and some times the Kalbasu (Labeo calbasu, Hamilton). These carps contribute approximately 75 percent fo the aquaculture production in India (FAO, 1997). As these carps are economically very important, research on cultivating these species of fish was initiated in India during early 1950s to study and understand the biology of these economically important species, particularly the major carps and to develop suitable technologies for various farming systems.
FAO (1972) has already pointed out that application of genetic principles to the selection of breeding stocks in commercial aquaculture lags far behind plants and other animals breeding. The main reasons for this according to FAO appear to be 1) lack of complete control by man of the reproduction phases 2) paucity of facilities for carrying out selection programmes 3) shortage of aquaculturists with genetic training and 4) lack of awareness among aquaculturists of the importance of genetic work. FAO considers that considerable time may elapse before adequate solutions to the above problems are found particularly in many developing countries where there is an immediate need to improve fish production. Now after a lapse of over two decades considerable concern has been shown to use genetics in aquaculture and enhance aquaculture production in most of the developing countries which are discussed in this review.
Genetic work on Indian major carps was initiated in the late 1950s soon after the success of induced breeding of these carps through hypophyzation (Chaudhuri, 1959) with simple interspecific and intergeneric hybridization among these carps and later between these carps and Chinese carps. This was followed by cytogenetic work to study the karyotypes of major carps and their hybrids in a comparative sense and also to relate the viability and fertility of their hybrids. During early 1980s the modern genome manipulation (chromosomal engineering) work was initiated to develop techniques to induce and produce gynogens and polyploids to build up homozygous inbred lines and triploid sterile fish respectively. Biochemical genetic studies were also initiated more or less simultaneously. Towards late 1980s, with the experimental production of transgenic major carps (Labeo rohita), molecular genetics work was also initiated.
The first ever project on selective breeding of Indian major carps was initiated successfully in the early 1990s, in India at the Central Institute of Freshwater Aquaculture, Kausalyaganga (Bhubaneswar) in collaboration with the Institute of Aquaculture Research (AKVAFORSK), Norway.
Recently some laboratories in India and other developing countries in the region have initiated developing methods to identify genetic markers, particularly in major carps through allozyme, mitochondrial DNA (mt DNA), random amplified polymorphic DNA (RAPD), restriction fragment length polymorphism (RFLP) and microsatellite techniques, for the genetic characterization and population genetic studies.
