The early history of freshwater prawn fanning was recorded in a conference on giant prawn farming held in Bangkok in 1980 (New, 1982). Since that time the aquaculture of freshwater prawns has spread to many new countries and production has expanded considerably. Full details of the current scale of freshwater prawn farming can be found in a number of recent papers (New, 1995; New et al 1995a, b); only a brief summary is provided here.
Nearly 91% of the more than 35 000 t global production of freshwater prawns through aquaculture in 1993 was produced in Asia. The global farm-gate value of farmed freshwater prawns has been estimated at nearly $US 194 million. All recorded commercial production is from one of the Asian species Macrobrachium rosenbergii. which has been transferred world-wide.
Outside Asia, significant production in 1993 (over 200 t/year) occurred only in Ecuador (800 t), the Dominican Republic (739 t), Brazil (700 t), and Puerto Rico (246 t).
Within Asia, the dominant producers have traditionally been Thailand, Taiwan and Viet Nam, though the statistics on Vietnamese production are contentious. Production in Thailand rose rapidly in the eighties, peaking at nearly 12 000 t in 1987. Production nearly halved by 1990, however, due partly to reduced farm-gate value due to greater availability and to changes in the potential revenue from other activities implying the same resources. The principal cause of the decline was the explosive expansion of marine shrimp farming, which diverted both government and private sector attention away from freshwater prawn farming. Thailand is now the premier producer of farmed marine shrimp. However, the trend for freshwater prawn production is again upwards, having recovered 10 514 t in 1993 (33% of the Asian total).
Nearly 38 % of the Asian total is produced in Viet Nam (12 000 t) but some of this total may be contributed by capture fisheries. Production from Taiwan peaked at over 16 000 t in 1991 but fell to about one third of this figure in the two years to 1993, due to so-called disease problems which were probably caused by poor water quality engendered by unsustainable rearing practices. Taiwan produced 17% of Asian farmed freshwater prawns in 1993.
Recently, substantial production of freshwater prawns has occurred in two of the nations of the Indian sub-continent, India and Bangladesh. Separate statistics on freshwater prawn production are not submitted to FAO by Bangladesh but it has been estimated that production may be as high as 5 000 t/year (NACA, 1995). Bangladesh, with a 40 000 t/year capture fisheries for freshwater prawns, is well-placed to develop its export market for farmed prawns. Interest in prawn production in India has been strong for some years and has generated considerable research effort, which is now paying off. Appearing for the first time in India's aquaculture statistics in 1990 at just under 200 t, production soared to 2 000 t in 1992 and nearly 4 000 t by 1993. In both Bangladesh and India, a considerable proportion of the output of farmed prawns is based on wild-caught juveniles, though hatcheries are being established, particularly in India. A balance between the need for increased and reliable seed supplies from hatcheries and the livelihood of the many existing wild seed collectors is being sought.
As mentioned above, commercial production of freshwater prawns is based entirely on Macrobrachium rosenbergii. though small quantities of other species are undoubtedly produced for local consumption and do not find their way into global statistics.
The other large species, amongst several smaller species indigenous to the Indian sub-continent, namely Macrobrachium malcolmsonii. has generated much research interest, particularly in India and in Pakistan. However, though M. malsomsonii grows to an impressive maximum size, commercial prawn culture in India is based on M. rosenbergii. The latter species appears to have a number of advantages, including a shorter larval life to metamorphosis (with consequent hatchery savings), excellent growth rate to marketable size, an established aquaculture technology, and its familiarity in global markets.
Though there have been some reports on M. rosenbergii in Pakistan, for example the book by Ahmed (date unknown) and some individuals claim that it is currently available in the capture fisheries, no specimens of this species were recorded by Ansari and Yacoob (1983). The research work carried out in Pakistan (Ansari and Yacoob, 1993; Yacoob, 1991; 1994 a, b; 1996) on the culture of M. malcolmsonii has proved most useful for the current feasibility study, providing details of growth rates, environmental conditions and other factors. However, all grow-out experiments in Pakistan to date have been based on stocking wild-caught juveniles. Yacoob (1987) successfully reared M. malcolmsonii to the final larval stage but was unable to produce postlarvae, due to technical problems.
It is recommended that the development of freshwater prawn farming in Pakistan be based on the well-known technologies for the culture of M. rosenbergii. which are being successfully applied for commercial purposes in many Asian and other countries. The introduction of M. rosenbergii into Pakistan, whether it be of broodstock or postlarvae, has no insuperable technical or logistic barriers. Also, there is no government objection to the introduction (Z. Altar, personal communication, 1995) of this species, which may already be indigenous. It would be prudent to carry out further studies on species composition in natural waters to confirm whether M. rosenbergii is indigenous to Pakistan or not. In any case, whether M. rosenbergii is introduced into Pakistan, or simply transferred from another country, the appropriate internationally agreed codes of practice (ICES, 1988, 1994; OIE, 1995; Turner, 1988) should be followed. Basing development on M. rosenbergii does not preclude further research work with M. malcolmsonii. for possible diversification at a later stage. Indeed, such work should be encouraged.
The feasibility study reported in this document has been based on the premise that the species of choice for the development of freshwater prawn farming in Pakistan will be M. rosenbergii. for the reasons stated above. For brevity, this scientific name will not be repeated further. In the rest of this report the word “prawn” should be read as synonymous with Macrobrachium rosenbergii.
The detailed rearing technology used for the culture of prawns has been well documented, both in practical manuals (New and Singholkha, 1985; Choudhury et. al. 1993) and in a recent review of the scientific literature (New, 1995). Copies of these documents were left with the Fisheries Development Commissioner (GOP), for dissemination within the GOP and the GOS. Further copies of the manual by New and Singholkha (1985) can be obtained from FAO in Rome, while copies of the manual by Choudhury et. al. (1993) can be obtained from BOBP, Madras.
In summary, prawn culture consists of two major phases, larval culture and grow-out, usually linked by some form of nursery rearing. Grow-out may be either monoculture or polyculture, usually with finfish. For the model considered in this report, monoculture has been selected because it enables the farmer to maximize revenue by managing his harvesting techniques to achieve more prawns of the most marketable size range. For immediate development in Sindh, a monoculture system is recommended. However, by this selection, the consultant does not wish to imply that there are no possible financial advantages of stocking prawns into existing carp ponds in Sindh. Polyculture of prawns with carp (or other finfish) could offer the opportunity to increase revenue from existing ponds but also complicates farm management. The technical assumptions (technology package) utilized in assessing the feasibility of monoculture freshwater prawn farming in Sindh, and of establishing a government pilot hatchery and demonstration farm are summarized in Appendix 6.
