WORLD AQUACULTURE 61 (CONTINUED ON PAGE 62) As floodwaters from the annual monsoon spreads across the floodplain, nutrients are released and primary production explodes over a very wide area. If adequate recruitment occurs, tremendous fisheries production follows. The main rivers in urban and periurban Dhaka are the Buriganga, Shitalakshya, Turag and Balu. Among them, the Buriganga, Tuag and Balu are highly contaminated with industrial pollutants. There are also many other small rivers in the periurban areas, such as the Bangshi and Menikhal. Moreover, some parts of the Meghna and the Brahmaputra are covered by the Sonargaon Upazila. The total area of these rivers in the urban and periurban is more than 10,000 ha with a total fish production of 2600 t. The dry season represents the most critical season for all species of fish and the greatest impacts occur at this time, when fish populations are at their lowest levels, fishery habitats are limited, predation is at a peak, and growth is slow. Competition for food is keen and pressure by fishermen remains high. Reductions, for whatever reason, in dry season aquatic habitat have the potential to reduce parent stocks to below replaceable levels. Minimum streamflow requirements are necessary to maintain healthy fish populations and to ensure that sufficient broodstock are available for repopulation of the floodplain during the next wet season (Table 2). The major species group (almost two-thirds) caught in beels and floodplains is currently reduced to a wide variety of small fishes. These include grazers and detritus feeders, small predators, and small pelagic plankton feeders. Carp, including major carps, large catfish and large fish in general, have greatly declined in abundance. Smaller climing perch, snakeheads, other catfish and resident species with the ability to tolerate low oxygen levels, comprise a major proportion of the catch in beels. Intentional stocking takes place in some of the smaller beels and enclosed floodplain areas. In these systems, the proportion of the catch consisting of major carps, silver carp, common carp and grass carp is substantial (Fig. 1). The river catch was, in the past, dominated in terms of value and production by the migratory clupeid known as hilsa (Tenualosa ilisha). Water pollution, reduced river flow, and intense fishing of juveniles have caused the disappearance of riverine hilsa. Other important species are Clupisoma garua, Pangasisus pangasius, Puntius sophore, Glossogobius giurus, Aorichthys seenghala, Labeo rohita, Catla catla, Wallagu attu, Mystus cavasius and Macrobrachium spp. A wide variety of other species (35) are caught, each contributing more than 1 percent to the catch. Inland Culture Fisheries Pond aquaculture and rice-fish culture (either rice and fish together or rice followed by fish) on seasonal farmland are examples of inland culture fisheries in and around Dhaka. Periurban aquaculture is now practiced to provide food, income and employment opportunities for many people in Dhaka. Increasing demands for live and fresh fish in Dhaka city markets has encouraged the expansion of periurban aquaculture. Pond aquaculture has spread widely in the past decade. Aquaculture systems generally use free water sources, but some receive commercial irrigation water or hire irrigation equipment. Pond fish culture: Many household have at least one pond in TABLE 1. Districts and upazilas in and around Dhaka, Bangladesh. District Upazila Dhaka Savar, Keraniganj Gazipur Gazipur Sadar, Kaliganj, Kaliakoir Narayanganj Narayanganj Sadar, Sonargaon, Rupganj TABLE 2. Areas of different types of water bodies of Dhaka, Bangladesh. Sector Water area (ha) Production (t) Rivers 10552 2618 Floodplains 4072 26252 Beels 4755 2744 Canal 1250 1573 TOTAL 57299 31771 TABLE 4. Percent of fish supply to Dhaka from periurban upazilas. Upazila Percentage of fish supplied to Dhaka city Savar 0 Keraniganj 8-10 Narayanganj Sadar 2 Sonargaon 5 Rupganj 10-12 Gazipur Sadar 10 Kaliganj 10-12 Kaliakoir 25-30 Bander 25 TABLE 3. Aquaculture production of different peripheral upazilas of Dhaka, Bangladesh. Domestic Pond Commercial Pond Upazila Area (ha) Production (t) Area (ha) Production (t) Savar 539 1754 - - Keraniganj 94 300 4.5 15 Narayanganj Sadar 543 2355 - - Sonargaon 288 860 - - Rupganj 191 493 33 122 Gazipur Sadar 1204 4042 61 172 Kaliganj 616 2075 68 240 Kaliakoir 806 2246 207 756 Bander 8 9 202 450
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