Expected increase in river salinity is likely to change the aquatic ecosystems of coastal Bangladesh. There are approximately 500,000 fishing households in the coastal area of the country (DFID 2007). Saline intrusion into freshwater habitats of fish is likely to change the composition of capture fishery during the dry season. Habitats of freshwater large fish, for example Catla ( _Catla catla_ ), Rui ( _Labeo rohita_ ), and Mrigal ( _Cirrhina mrigala_ ), are likely to decline in the wild.<sup>39</sup> Reductions in the wild are also expected for small indigenous freshwater fish species, for example Bacha ( _Eutropiicthyys vacha_ ), Bata ( _Mugil parsia_ ), Batashi ( _Pseudeutropicus atherinoides_ ), Chela ( _Salmostoma argentea, Salmostoma phulo, Salmostoma bacaila_ ), Darkina ( _Esomus danricas, Rasbara daniconius, Rasbara rasbora_ ), Kajuli, Baspata ( _Ailia coila, Ailicthys punctate_ ), Kash Khaira ( _Chela laubuca_ ), Kholisha ( _Colisa fasciatus_ ), and Tengra ( _Mystus tengra_ ). The optimum level of surface water salinity is less than 4ppt for Golda/giant freshwater prawn ( _Macrobrachium rosenbergii_ ) and ten to 20ppt for brackish water Bagda/Black Tiger shrimp ( _Penaeus monodon_ ). Golda production in the wild<sup>40</sup> is expected to decrease and Bagda production on monoculture farms is expected to increase.<sup>41</sup> Expected increase in river salinity is likely to trigger changes in the ecosystems of the Sunderbans<sup>42</sup> mangrove forest, the UNESCO Heritage site. The most commonly found trees in Sunderbans are Sundari ( _Heritierafomes_ ), Gurjan ( _Dipterocarpusturbinatus_ ), Gewa ( _Excoecariaagallocha_ ), Guran ( _Ceriopsdecandra_ ), Keora ( _Sonneratiaapetala_ ), and Kankra ( _Bruguierasexangula)_ .<sup>43</sup> Among these, Sundari is the single most dominant and important species of Sunderbans, with the highest market value. The diameter of the trunk of the Sundari

> 39 Although these fish species can tolerate salinity up to 10–11ppt, they grow better around 5ppt. Estimates indicate that river water area with a level of salinity <5ppt would decline by 4 to 12 percent from the baseline by 2050 with climate change. See Pillay and Kutty (2005).

> 40 Spawning grounds for Golda prawn are likely to move upstream as freshwater is essential for Golda juveniles.

> 41 In 2010, estimated combined production of shrimp and prawn was around 98,000 tonnes, Shrimp and prawn are major exports of Bangladesh and generated US$412 million in 2009–2010. See Belton et al. (2011) for details.

> 42 The Bangladesh Sundarbans merges with the Sundarbans forest of West Bengal in India and together they make up the largest continuous tidal mangrove forest area of the world. Sundarbans is a UNESCO site. It is a unique ecosystem and a rich wildlife habitat with 334 recorded plant species, 270 species of birds, 42 species of mammals, 35 reptiles, eight amphibian species, and at least 150 species of commercially important fishes. The name Sunderbans is coined from Sundari trees. The Bengali word “ban” (pronounced as “bon”) means forests.

> 43Tolerance for salinity varies across species. For example, Sundari and Kankra are freshwater-loving species with lower ecological amplitude. Guran, Gewa, and Keora are moderately salt tolerant with wider ecological amplitude. See Islam and Gnauck (2007).

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