The Indian major carps, the catla, the rohu and the mrigal are the natural inhabitants of the perennial rivers network of India, Pakistan and Bangladesh and, enjoy a wide distribution. These species are well established in almost all the rivers and reservoirs where they have been transplanted. Substantial research has been carried out to study the biological aspects and propagation of these carps after the initiation of systematic research on inland fisheries in the beginning of 1950s. Based on this information culture technologies were developed resulting in intensive and extensive composite (multispecies) culture; production levels increased from 0.6 t/ha/year to 10–15 t/ha/year. At the same time three decades of effort to develop improved varieties of carps through cross breeding (hybridization) did not result in the production of any commercially viable hybrid varieties.
The Cytogenetic investigations mainly on karyotypes have shown that though these major carps have their own distinct morphological features, genetically they appear to be very closely related as indicated by not only their karyotypes but also by their isozyme and DNA profiles.
The information available on biochemical genetic studies is not very complete. However, recent efforts in this area and in DNA analyses have resulted in the development of some methodologies for the identification of genetic markers in the case of catla, rohu and mrigal. These techniques may be effectively used for stock identification and to study genetic variation in the individuals of a particular species or putative land races. These methods were hitherto not developed and consequently no early studies were conducted to investigate whether there exist different populations or races within a given species of major carps.
With the development of allozyme, RAPD, mtDNA RFLP and microsatellite techniques, some preliminary investigations were carried out which indicated the existence of genetic variations between the stock of different major seed producing hatcheries and also between the hatchery and wild populations of catla.
Differences in isozyme markers have been also noticed among rohu of different river systems namely, Rivers Ganga, Gomati, Yamuna, Sutlej and Brahmaputra.
Of the three species of Indian major Carps, rohu grows relatively slower in carp culture systems, while catla and mrigal exhibit comparatively better growth. Because rohu is a highly prized fish, efforts are being made to improve genetically the species through selection. There appears to be regional preference, for a particular species in India. While rohu is preferred in most of the states in the Eastern region, catla is popular in the Southern states, especially in the provinces of Karnataka and Andhra Pradesh. Genetic improvement of catla has been taken up in Karnataka province.
The aim of current selection projects is to provide correct breeding procedures to the hatchery managers and to develop genetically superior lines that can produce quality seed which can grow to over a kilogram within one year under intensive composite farming system.
The slowest growing among the major carps, L. calbasu, is an up-coming species and gaining popularity. As mentioned earlier, this species has good resistance against parasite infection and can stand rough handling to a better extent than other major carp species.
In almost every carp farming nation in Asia, proper use of the genetic potentials of these species has not been sincerely attempted, probably due to the preoccupation to develop suitable culture technologies with the already existing resources and the need to meet the immediate and urgent protein requirement of the masses in their respective nations. Now many of these nations in Asia, after achieving the goal to a notable extent in rising the average fish production levels through improved culture technologies, have started realizing that quality improvement is necessary to increase further the quantity. These two aspects cannot be separable. During the coming decades, if aquaculture is to be a viable industry, it must be supported by technologies which ensure sustainable higher productions. Conservation and protection of the genetic resources and exploitation of genetic potentials of the species of fish to their optimum levels appears to be an excellent immediate path way to achieve the goal.
Most of the nations especially in Asia have already initiated action by taking up conservation of genetic resources and genetic improvement activities of important species. The major carp culturing nations India, Bangladesh, Pakistan, China, Thailand, Vietnam etc. have already started working on the job either independently or in a collaborative manner among themselves or with other advanced nations. The International Network for Genetics in Aquaculture (INGA) is coordinating fish genetic research among all the member countries. The above mentioned countries are among the member countries under the INGA network. India, Philippines and Vietnam have collaboration with the Institute of Aquaculture Research (AKVAFORSK), Norway on selective breeding programmes. Recently the International Centre for Living Aquatic Resource Management (ICLARM) has launched a carp genetic improvement project in which the research on genetic improvement of carps is supported through providing funds and also coordinating the research among the INGA member countries of Bangladesh, China, India, Indonesia, Thailand and Vietnam. Exchange of carp germplasm among interested countries has been also planned under this programme. The coming decade may witness an overall improvement in the aquaculture sector through the systematic and sustainable exploitation of fish genetic resources and the wider use of genetically improved varieties in aquaculture system.
