Bhutan has a fairly good potential for development of its fisheries in spite of the climatic and infrastructural limitations existing at present. The adviser considers that the rivers of Bhutan could support a larger fish population than they appear to have, judging from the food available in them for fish.
Improved programmes of stocking rivers and lakes with selected species could reinforce the already existing fish populations, using untapped food resources and thus allowing a higher fishing pressure. This would result in direct benefit for the communities along the river banks where, if they are allowed to fish, even with some restrictions, they would very much improve their protein diets.
As a secondary development aspect, sport fishing could also be improved for the tourist trade.
Aquaculture, in its various forms, is another way of improving fisheries in the country. At present, pond culture, cage culture and rice-cum-fish culture are unknown in the country. In the opinion of the adviser, their introduction and expansion would be an effective means of increasing the available amount of fresh fish for human consumption. It would also help to reduce, in some measure, the importation of fresh and dried fish from India.
Besides surveying the existing aquatic resources for development of fisheries and fish culture, the Fisheries Development Adviser selected possible sites for construction of fish ponds and farms for fish culture. About 80 ha could be used in both the cold water and temperate zones and an additional 40 ha were judged suitable for development in the tropical zone (See Appendix 3).
Since the development of riverine and lake fisheries is a long-term project, the FAO adviser attempted short-term aquaculture experiments to assess potential production figures. He persuaded interested people to construct their own ponds for fish culture trials and, as a result, Makshi Lam Dorji, built one pond in his field. At the same time another pond was constructed at Wangchutaba near the hatchery. Thus two ponds measuring 91 m2 and 50 m2 were made available in a short time in Thimbu at a cost of N150 and N50 respectively.
The ponds have facilities for filling and draining when required, although they are running-water ponds.
A 0.6 ha pond was also constructed at Thimbu near the Thimbu Chu River with the help of a bulldozer at a cost of N18 000 and about N5 000 more would be needed to attain a more desirable depth of 1 to 1.5 m. The cost per hectare of construction with a bulldozer could be estimated at about N50 000.
For the experimental trials carried out by the adviser, a consignment of 1 800 fingerlings (average weight 5 g) of common carp (Cyprinus carpio var communis) was brought from Gauhati (Assam, India), located at an approximate altitude of 100 m, on 13 May 1976 and was initially kept in a cement pond (234 m altitude) by Dasho Rimpochy at Phuntsholing. The carp, after initial acclimatization, were transferred gradually and, as per need, to different ponds. The details of experiments conducted at Thimbu, Sarbhang and Kanglung Agriculture Farm are given in Appendix 4.
The experiments indicate that a fish production of 450 kg/ha in three months at an altitude of 2 392 m at Thimbu is possible. It was not possible to evaluate the pond production completely at Wangchutaba as the fish were eaten by otters in September. In the case of the pond at Kanglund Agriculture Farm and Sarbhang, the water from the pond could not be drained nor could all the fish be removed. However, keeping in mind the growth of fish sampled and presuming 80 percent survival, it could be inferred that the production in Kanglung in three months and in Sarbhang in five months, could easily have been up to 500 kg and 900 kg/ha respectively.
Places like Thimbu (2 392 m) have a growing period of seven months, with a period of nine months for Wangdi Phodrang and 12 months for Sarbhang where culture of common carp could give still better results.
The adviser also distributed fingerlings to a number of people who showed keen interest and constructed small ponds. The fish were still in these ponds and the growth and behaviour should be monitored.
On 11 December 1976 it was observed that the water temperature in the pond at Wangchutaba (one metre deep) in the morning was 3°C and, in spite of a sheet of ice forming on the surface of the pond, no mortality of fish occurred. This resistance to difficult conditions impressed people and convinced them of the possibility of acclimatizing common carps at high altitudes.
Rice-cum-fish culture is a common practice in many parts of the world but is unknown in Bhutan despite the fact that there are over 20 000 ha of paddy fields cultivated. These holdings are small but could be a source of supply of protein food for the farmers and their families engaged in rice paddy cultivation. Considering that 10 percent of these paddy fields are to be provided with adequate irrigation facilities, a surface area of 2 000 ha is readily available for fish production use.
A phased programme of rice-cum-fish culture could be initiated immediately by bringing into production 100 ha of rice fields each year. A stocking density of 500 fingerlings/ha (50 mm average length) is suggested. Based on 50 percent survival and an average growth of 50 g/year, a production of 1.25 t of fish per 100 ha would be available annually to the small farmers. When all the available 2 000 ha are brought under fish cultivation, a minimum of 25 t of fish would be available from rice fields alone. The total potential of rice fields in Bhutan, with provision of adequate irrigation facilities and when fully utilized, will be around 250 t/year, even at this low level of production.
The practice could also be extended to fields which lie fallow for part of the year, provided adequate irrigation facilities are available and a water depth of 25 cm is ensured throughout the rearing period. Such fields would serve as paddy ponds for fish culture.
Cage culture could be profitable undertaken in stream margins near towns or villages, making use also of sewage discharge. Split bamboo or wooden cages (1.5 × 1 × 0.75 m) could be installed and stocked with common carp fingerlings (50–75 mm) at a density of 100 fingerlings/m2. Such cages could also be installed in areas where manure is discharged into streams. Several locations where small-scale cage culture could be started have been noted by the fisheries development adviser near Tashigang, Tongsa, Shemgang, Samdrupjongkhar, Sarbhang, Phuntsholing, Paro and Thimbu.