Abstract:To understand the present status of fish diseases and their remedial measures taken by the fish farmers, a questionnaire survey and Participatory Rural Appraisal (PRA) tools including Focus Group Discussion (FGD) were conducted in seven districts of Bangladesh. In total 196 farmers were interviewed and nine FGD sessions were conducted. Disease occurs immediately after stocking (24%) and during the rainy season (21%) followed by cold season (19%). Mortality, abnormal swimming and feeding behavior, unusual appearance, some localized lesions and reduced growth are the main clue to recognize the fish disease. The most frequently observed diseases were epizootic ulcerative syndromes (18.72%) followed by tail and fin rot (13.19%), red spot (11.49%), gill rot (9.36%), parasitic disease (8.93%), broken prawn antennae (7.23%), and other environmental and nutritional diseases. To cure these diseases, farmers applied the following treatments: lime and potash, liming, lime and salt, lime alone, salt and potash, antibiotics, various chemicals, high doses of vitamin C, complete water exchange, and transport to another pond. This study showed that diseases can play important roles in freshwater aquaculture, but this role is often not recognized due to a lack of knowledge and veterinary backstopping services.

A pot-culture experiment was conducted in open-field conditions with highly cultivated locally transplanted (T) aman rice (Oryza sativa L.) named BR-22 in arsenic (As)-amended soil (0, 1.0, 5.0, 10.0, 20.0, 30.0, 40.0 and 50.0 mg kg -1 As) of Bangladesh to see the effect of As on the growth, yield and metal uptake of rice. Arsenic was applied to soil in the form of sodium arsenate (Na 2 HAsO 4 ). Arsenic affected the plant height, tiller and panicle numbers, grain and straw yield of T-aman rice significantly (P B 0.05). The grain As uptake of T-aman rice was found to increase with increase of As in soil and a high grain As uptake was observed in the treatments of 30-50 mg kg -1 As-containing soil. These levels exceed the food hygiene concentration limit of 1.0 mg kg -1 As. However, the straw As uptake varied significantly (P B 0.05) from a low concentration of As in soil (5 mg kg -1 ) and the highest uptake was noticed in 20 mg kg -1 As treatment.

Abstract:A study was carried out on the optimal dose of inorganic fertilizer used in carp polyculture system over a period of 10 months. Three treatments were assigned: without inorganic fertilizer, with the application of 100 kg/ha/month inorganic fertilizer and 150 kg/ha/month inorganic fertilizer as T1, T2 and T3, respectively. Each treatment had three replications. The selected indigenous carp species were Rui (Labeo rohita), Catla (Catla catla) and Mrigal (Cirrhinus mrigala), and exotic carp species were silver carp (Hypophthalamichthys molitrix), grass carp (Ctenopharyngodon idella), common carp (Cyprinus carpio) and thai sarpunti (Barbodes gonionotus). The average water area of the experimental ponds was 0.11± 0.01 ha and average depth of water in all ponds was 1.26 m. The treatments showed no effect on water temperature, dissolved oxygen, alkalinity and pH. The fish production was significantly higher (P>0.05) in both the treatments T2 and T3 than that of T1 where no inorganic fertilizer was used. But there was no significant difference between T2 and T3 and T2 was with lower dose inorganic fertilizer (100 kg/ha/month) than T3. Therefore, 100 kg/ha/month inorganic fertilizers may be suggested in carp polyculture system for better production.

The production of wet-season rice (mid-August to mid-December) followed by dry-season (mid-December to mid-August) shrimp (Penaeus monodon) is a common farming system in the south-western coastal region of Bangladesh. Experiments were conducted in the farmers' fields during the rice- and shrimp-growing seasons of 2004, 2005 and 2006, with the aim of improving the total farm productivity of the rice-shrimp system through technological intervention. During the wet season of 2004, yield responses of different high-yielding (BR23, BRRI dhan 40 and 41, HR1 and 14) and traditional (Horkoz) rice varieties were evaluated for their responses to the prevailing salinity-influenced environment and integrated with: (i) GIFT (genetically improved farmed tilapia) strain of Nile tilapia (Oreochromis niloticus) alone; (ii) GIFT and giant freshwater prawn (Macrobrachium rosenbergii) at a 1:1 ratio; and (iii) prawn alone at a stocking density of 10,000/ha. In the 2005 rice season, the previous season's best-yielding rice varieties (BR23, BRRI dhan 40 and 41) were cultivated, integrated with a similar aquaculture species combination but at a reduced stocking density of 5000/ha. In the dry seasons of 2005 and 2006, the production of black tiger shrimp (P. monodon) was evaluated for three stocking patterns: (i) single stocking (5/m2); (ii) double stocking (3/m2 followed by 2/m2); and (iii) double stocking (2/m2 followed by 3/m2). Among the rice varieties, BR23 and BRRI dhan 40 performed best, with similar yields averaging about 5 t/ha. The reduced density of 5000/ha actually gave better fish and prawn yields, resulting in additional average production of 258 kg of GIFT and 71 kg of prawn/ha. The net return from GIFT alone was Tk10,858/ha and that from prawn was marginal or negative. Single and double stocking of shrimp did not show any significant differences in body weight, survival rate and yield, with the values ranging from 20 to 24 g, 26 to 35% and 289 to 380 kg/ha, respectively. There were considerable variations in survival and production within each treatment, particularly because of higher shrimp mortality in the replicate ponds that had comparatively shallower water depth during the culture period. Single stocking resulted in average net returns as high as Tk67,500/ha and was considered more suitable in rotation with rice.

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