The most actively involved countries, besides India, on genetic research of Indian major carps are Bangladesh, Vietnam and Thailand. Information is generally lacking regarding genetic work in Pakistan and Burma.
Research on genome manipulation is being carried out and successful induction of meiotic and mitotic gynogenesis was achieved at the Fisheries Research Institute Freshwater Station, Mymensingh. Clonal lines of L. rohita produced by meiotic gynogenesis in the F generation were reported to have been produced. (Hussain et al., 1994 b and Hussain et al., 1997). Successful induction of triploidy was also reported in L. rohita (Islam et al., 1994).
Bangladesh has also initiated selective breeding work on C. catla for genetic improvement. For this, catla were collected from different river systems and genetic characterization is being carried out by applying electrophoresis and morphological methods.
As indicated by the surveys conducted in Indian hatcheries (Eknath and 1990 and Basavaraju et al., 1997), the investigations in Bangladesh have more or less shown the same trend. The existence of 400 carp seed producing hatcheries has been reported from Bangladesh. These hatcheries have been engaged in the production of seed since the 1970s. Some 31 billion spawn are reportedly produced annually. Problems mentioned with regard to hatchery produced seed in India have been also common in Bangladesh. Deterioration of hatchery bred stocks as indicated by retarded growth, morphological deformities and increased incidence of disease has been reported in recent years due to poor brood stock management. The data collected from several fish hatcheries located in Jessore, Comilla and Mymensingh revealed that most of the hatchery operators have no basic idea about brood stock management such as recruitment of new breeders at periodic intervals in the stock, optimum density of the brood stock and their proper feeding (Hussain and Mazid, 1997). These hatchery procedures lead to unconscious negative selection due to the use of undesirable size of brood fish and generation after generation of mating the related spawners from a small population.
Currently, Bangladesh is engaged in characterization of different land races of catla and rohu by the assessment of meristic and morphological characters, genetic fingerprinting of riverine stocks of catla using molecular techniques and karyotyping to assess ploidy of rohu and mrigal. Developing breeding plans for stock improvement of catla and induction of gynogenesis and production of genetic clones in rohu are part of a genetic improvement programme for carps in Bangladesh.
Thailand has an elaborate genetic improvement programme, not only on carps but also for other species such as tilapias, catfishes, freshwater prawns, seabass, oyster, and aquarium fish. Among Indian major carps L. rohita has been currently taken up in Thailand for genetic work. Nineteen pairs in 1968 and 250 fish in 1969 were introduced into the country. The species is propagated through hatchery breeding and stocking in reservoirs and swamps where they have been already become established. It is also cultured in ponds. The production of rohu in 1994 was estimated at 1,783 tones ranking third in both weight and value among the carp species cultured in Thailand (Nuanmanee Pangthana, 1997).
Genetic studies on rohu have been carried out with regard to the growth rate of the species raised in cages and to estimate the heritability as well as the genetic, phenotypic and environmental correlation for body weight, total length, body depth, head length and girth of fish at different ages (Dupsuksamran. 1987).
Mrigal was introduced into Thailand during 1980 and 82. A consignment of 100 fish was first introduced from Bangladesh. Later in August 1982 eight pairs of brood fish weighing 700–800 g and 500 fingerlings were brought to Kalasin Inland Fisheries Station. Like rohu the propagation of mrigal is also carried out through hatchery breeding and the seed is stocked in reservoirs and swamps. The species has now become established and is available throughout the country.
Thailand wants to set up a National Breeding Programme for hatchery produced carps and tilapias; among the Indian carps, L. rohita has been selected. The Central Institute of Freshwater Aquaculture (CIFA) is providing the improved rohu strain under the International Network for Genetics in Aquaculture (INGA) programme.
Vietnam, like India, Thailand and Bangladesh, is one of the member countries of INGA but also the carp genetic improvement programme in Asia. The Indian carp species included in carp culture practices in Vietnam are the rohu and mrigal.
Vietnam has an elaborate selective breeding programme for mrigal. Mrigal production is mainly from north Vietnam, but this species is not considered as important in the south. Of the 200,000 tons production from freshwater, mrigal contribution was reported to be 45,000 tons in north Vietnam (Bentsen et al., 1996).
In north Vietnam, sexual maturity in mrigal occurs at two years of age as in India. The breeding process is repeated three times in a season. It has been reported that the first and the second breeding yield better quality seed than the third. This is because young and small brooders normally mature and spawn earlier in the season and, like in other regions, early produced fry fetch higher price. This tendency to prefer to use early mating and small sized brood stock may lead to selection for small size and early maturity.
The base population of mrigal consisted of about 1000 fingerlings, imported from only one source, i.e. the Thangon state fish Farm in Laos in 1984 to the Thu Due Fish Farm of Research Institute for Aquaculture No. 2 (RIA 2) with the support of the Interim Mekong Committee. Another consignment of 10 pairs of breeders were imported from the same source in 1986. At the Fish Farm of the Research Institute for Aquaculture No. 1 (RIA-1) about 4–5 generations have been produced from only 6 males and 6 females which were transported from RIA-2 from the original stock. Because of the repeated production from a limited stock of 6/6 brood fish, the growth rate was observed to decline year by year. Deformities have been consistently observed in about 5–7 percent of the fish. The fish also have been reported to mature at lower age and lower body weight.
Vietnam is planning to take up individual (mass) selective breeding programme for mrigal. However, before the start of the programme, the base population has to be upgraded. Thus, Vietnam has planned to directly import wild populations of mrigal from three different river systems in India, consisting of about 2000 fry from each river. The two main goals of Vietnam for aquaculture of mrigal carp are a high growth rate and a high proportion of females, as males are 60–70 percent of the female body weight at market. This is true in most other carps as well A detailed plan of the selection programme for mrigal in Vietnam has been drawn out by Bentsen et al. (1996).
