Abstract
Impact of heavy metal and water quality on breeding and culture of freshwater prawn was evaluated through four experiments in Mymensingh and coastal area of Bangladesh from 2006 to 2008 with a view to developing a sustainable prawn post larvae (PL) production and culture technology to fulfill the demand of prawn PL and economic benefit of the rural people as well as to increase the export earning of Bangladesh. Suitability of brine solution and crude salt for production of prawn post larvae were investigated in the first experiment. Seven treatments were used in rearing prawn post larvae. In T1, 100% sea water; T2, 100% brine; in T3, 100% crude salt; in T4, 75% sea water and 25% crude salt; in Ts, 75% brine and 25% crude salt; in T6, 50% sea water and 50% crude; in T7, 50% brine and 50% crude salt were used. The survival rate of prawn larvae were 50.92% (Ti), 48.88%(T2), 0%(T3) 42.66%(T4), 40.77%(Ts), 15.73%(T%) and 14.56% (T). The results showed that sea water was the best for PL production and brine also good. But crude salt was not proper media for larvae rearing of prawn. Heavy metal concentration of crude salt was not similar to the heavy metal of sea water. In experiment 2, artificial sea water was evaluated for production of prawn PL. There were three treatments and three replications of each. In T1, artificial sea water; in T2, artificial sea water 50%+ brine50% and in T3, brine were used. The survival rate of prawn larvae were 52.32% (T1), 49.28% (T2) and 48.66 % (T3). This result indicated that artificial sea water is the best media for larvae culture due to pesticide or other heavy metal contamination and free from pathogen In experiment 3, impacts of heavy metal, soil and water qualities on growth and survival of giant freshwater prawn were observed at three upzillas of three divisions such as Khulna (Kochuya upzilla in Bagherhat), Barisal (Amtoli upzilla in Borguna) and Dhaka (Fulpur upzilla in Mymensingh). The stocking density of juveniles was 100 individuals/decimal. The mean values of water quality parameters such as temperature, transparency, dissolved oxygen (DO), pH, total alkalinity, ammonia-nitrogen, nitrate- nitrogen, nitrite-nitrogen, phosphate-phosphorus and Chlorophyll-a were found to be ranged from 29.30 to 30.47 °C, 28.00 to 33.60 cm, 5.39 to 7.07 mg/l, 7.26 to 7.79, 115.17 to 146.80 mg/l, 0.08 to 0.22 mg/1, 0.07 to 1.28 mg/l, 0.02 to 0.48 mg/l, 0.49 to 1.09 mg/l and 58.82 to 115.85 μg/l, respectively. Significant differences (P<0.05) were observed in the mean values of transparency, temperature, pH, and nitrate- nitrogen, phosphate-phosphorus and Chlorophyll-a among the treatments. The values of sediment quality parameters like pH, potassium, phosphorus, sulphar and organic carbon were ranged from 5.80 to 8.10, 0.19 to 0.98 me/100g, 1.39 to 16.09 ppm, 22.15 to 118.00 ppm and 0.38 to 1.15 mg/l, respectively. The significant difference (P<0.05) was observed for pH, potassium, phosphorus, sulphar among the treatments. prawn performed comparatively higher growth rate (65.83 g) and average daily gain (0.43 g) in treatment 1 than in treatments 2 and 3. Similarly higher survival rate (89%) was also record in treatment 1 than treatments 2 and 3. The study clearly demonstrates that some parameters of soil and water quality had influence on growth and survival of prawn in pond culture. In experiment 4, the levels of five heavy metals (Cu, Cd, Zn, Pb, and Fe) in different samples (water sample-18, sediment sample-18 and prawn species sample -18) collected from Satkhira district were evaluated to observe the heavy metal contamination of water, sediment and prawn of different prawn Ghers (big pond). Samples were collected from surface and ground sources from different Ghers and were used for analyses of some metal ions viz. Cu2+, Cd2+, Zn2+, Pb2+ and Fe3+. The average concentration of Cu from the present study varied from 76.92 ugg for sediment, 0.056 ppm for water and 51.23 μg g' for prawn, average concentration of Cd was 3.59 μg g' for sediment, 2.43 ug g'' for prawn and 0.0115 ppm for water, average concentration of Zn was 152.112 p 2 μg g1 for sediment, 65.72 μg g' for prawn and 0.017 ppm for water, average concentration of Pb was 58.16 μg g1 for sediment, 31.80 ug g1 for prawn and 0.034 ppm for water and lastly the average concentration of Fe was 7548.09 μg g' for sediment, 269.14 μg g' for prawn and 0.061 ppm for water, respectively. Among 54 samples of water most of them were alkaline in nature and the concentration of Pb and Fe were higher than permissible limit and Cu, Fe and Zn in sediment samples were present higher amount than allowable limit. So prawn was mostly affected by contaminated water and sediment. The ranges of these metals were varied from source to source.