Environmental impact of aquaculture-sedimentation and nutrient loadings from shrimp culture of the southeast coastal region of the Bay of Bengal

Nutrient loadings were measured for surface seawater and bottom sediments of semi intensive and improved extensive shrimp culture pond, adjacent estuary, and fallow land in the south east coastal region of Bangladesh during August, 2000—January, 2001 to evaluate the impact of shrimp culture. The mean levels of nutrients found in the pond surface water were 108 780 mg/L for CaCO 3, 0 526 mg/L for NH + 4 N, 3 075 wt% for organic carbon, 7 00 mg/L for PO 4 P, 5 57 mg/L for NO 3 N, and 7 33 mg/L for chlorophyll a. The maximum mean value of H 2S(0 232 mg/L) was found in estuarine water. Nutrients loading were found to be decreased with distance from the shrimp farm discharge unit in estuarine water. The mean level of organic matter, total nitrogen, and organic carbon were found in higher concentrations in sediments of cultured pond compared to bottom soil of adjacent fallow land at the same elevation. Extractable Ca values were found in higher concentration(550 33 ppt) in adjacent fallow land, as the shrimps for molting in shrimp ponds use extractable Ca. The relation between seawater H 2S value and sediment pH ( r= -0 94); sediment organic carbon and sediment pH values ( r= -0 76), sediment total nitrogen and sediment pH ( r= - 0 74) were found to be highly negatively correlated. Whereas the relation between seawater H 2S value and sediment total nitrogen ( r= 0 92), water NH + 4 N and sediment pH ( r= 0 66) were found to be positively correlated. The results revealed that load of nutrients at eutrophic level in estuarine water, and decrease of soil pH; leading to acid sulphate soil formation indicates a negative impact of shrimp culture.

Optimized Composition of Functional Bacteria for Bioremediation of Sediment Environment of Shrimp Culture

After the single-strain abilities of organic-pollutant-degrading bacteria in bioremediation of sediment environment of shrimp culture are determined, the multi- strain degrading effect of the compositions of different strains is measured. The results indicate that the multi-strains groups have higher degrading ability than the single -strain groups. Three-strain groups are better than two-strain groups, and four-strain groups are better than three-strain groups and five-strain groups, the groups composed of strains Lt7222, Lt7511, Fc6308 and Gy7018 has the best degrading effect, the CODMn removal rate is 73.2 % in 66 h, and gets to 82.7 % in 114 h, 30 % higher than that of the best single-strain group; Groups of Lt7222, Lt7511, Lt7451 and Gy7018 are the second, whose CODMn removal rate is 82.1 % in 114 h. It is suggested that multi-species bacteria be used as functional bacteria in bioremediation of mariculture environment.

Assessment of Water Quality in Shrimp Culture Areas of the Mekong Delta

Water quality was investigated in shrimp culture areas in Cau Ngang, Tra Vinh where three culture systems were found in the same area to assess the impact of intensification of shrimp culture on the surrounding environment. Three culture systems were selected including intensive, semi-intensive and rice-shrimp alternated culture for the study. Monthly assessment of physical and chemical parameters of water and biotic parameters were done for a period of one year from March, 2009 to February, 2010 in the canals surrounding the culture systems. The physical chemical parameters of water recorded include temperature, pH, dissolved oxygen, chemical oxygen demand （COD）, total suspended solids （TSS）, total ammonium （TAN）, nitrite （N-NO2）, nitrate （N-NO3） and total nitrogen （TN）, total phosphorus （TP） in both water and sediment. Zooplankton and zoobenthos were determined quantitatively and qualitatively using zooplankton nets and Petersen grabs, respectively. The results indicated that most of water parameters were not significantly different between culture systems and were in suitable ranges for aquatic life within the national standard criteria except DO, TSS and TP at some periods. DO concentration in rice-shrimp system was significantly lower than that in other systems. TSS and TP concentrations both in water and sediment were high exceeding the limit ranges （〉 100 mg/L）. The occurrence of some zooplankton and zoobenthos species indicated that all systems were polluted at 13 level （mesosaprobic） in which the rice-shrimp alternated culture system subjected to more environmental fluctuation not only by shrimp culture but also rice cultivation and salinity variation between dry and rainy seasons.

COMPARATIVE STUDIES ON NITROGEN BUDGETS OF CLOSED SHRIMP POLYCULTURE SYSTEMS

April to October, 1997 comparative studies on the nitrogen budgets of closed shrimp polyculture systems showed that, in all the studied polyculture systems, nitrogen from feeds and fertilizers were the main input items, which comprised 70.7%-83.9% of the total input nitrogen, 3.2%-7.4% of which was provided by nitrogen fixation. It was in monoculture enclosures (Y 4, Y 11 and Y 12) that the percentage reached the maximum value. The output nitrogen in harvested products comprised 10.8%-24.6% of total input nitrogen, and the highest percentage, 24.6%, was found in shrimp fish tagelus polyculture systems. In shrimp monoculture and shrimp fish polyculture systems, they were 19.1% and 21.9%, respectively. The nitrogen utilization efficiency was different and varied from 12.2% to 20.1%. The highest, 20.1%, was found in shrimp fish tagelus polyculture systems, and the average of 20.0% was found in shrimp tagelus polyculture systems. The lowest, 12.2%, was found in shrimp monoculture systems. All the nitrogen utilization efficiencies in shrimp fish systems or shrimp scallop systems seemed to be higher than that of the monoculture system, but they showed little statistical difference. The main outputs of nitrogen were found in sediment mud, and comprised 48.2%-60.8% of the total input, the lowest percentage was found in shrimp fish tagelus polyculture systems, and the highest percentage in shrimp scallop systems. During the experiment, nitrogen lost through denitrification and ammonia volatilization comprised 1.9%-6.2%, averaged 2.8%, of the total input, and the loss through seepage comprised 5.9%-8.9% of the total. The estimated nitrogen attached to the enclosure wall comprised 3.7%-13.3% of the total, and was highest in shrimp monoculture systems. Compared with the classic shrimp farming industry, the closed shrimp polyculture systems may improve the nitrogen utilization efficiency, and hence reduce the environmental impacts on coastal waters. The nitrogen discharging rates for all the studied polyculture systems ranged from 3.0% to 6.0% of total input nitrogen.

Bacterial and eukaryotic community interactions might contribute to shrimp culture pond soil ecosystem at different culture stages

Sedimentary bacterial and eukaryotic communities are major components of the aquatic ecosystem.Revealing the linkages between their community structure and interactions is crucial to understand the diversity and functions of aquatic and soil ecosystems.However,how their diversity and assembly contribute to their interactions on time scale is unclear.This study examined sedimentary bacterial and eukaryotic communities in shrimp culture ponds at different culture stages.The most abundant bacteria were Proteobacteria(38.27%),whereas the most abundant eukaryotes were Chytridiomycota(27.48%).Bacterial and eukaryotic diversities were correlated(P<0.05),implying the strong interactions between bacteria and eukaryotes.Results showed that the bacterial and eukaryotic communities became increasingly similar on a local scale along with the shrimp culture.Only the eukaryotic community significantly increased in similarity along with the shrimp culture(P<0.05),suggesting that the sedimentary eukaryotic community structure is sensitive under shrimp culture.Co-occurrence network modeling indicated that positive microbial interactions were dominant.The homogeneous selection was the major driver of community assembly.Bacterial diversity negatively correlated with operational taxonomic units and positive links in networks(P<0.05),whereas eukaryotic diversities positively correlated with positive links in networks(P<0.05).This study broadens our knowledge about sedimentary microbial diversity,community assembly,and interaction patterns on time scale,providing a reference for the sustainable management in aquaculture production.

A Comparative Study of Intensive Litopenaeus vannamei Culture on Four Bottom Substrates Without Water Change

The effect of four bottom substrates, oyster shell powder(OP), sugarcane bagasse(SB), a mixture of OP and SB(OS) and fresh soil(FS), on the water quality and bacterial and zooplankton density of intensive shrimp(Litopenaeus vannamei) culture tanks without water change and the growth performance of cultured shrimp were compared in this study. At the end of a 110 days culturing trial, the total ammonium-N(TAN) of the water on SB and the nitrite nitrogen(NO2-N) on OS was significantly lower than that on the other substrates(P<0.05), which coincided with the high density of ammonium- and nitrite-oxidizing bacteria in the water on SB and OS, respectively. The concentration of chlorophyll a(Chl a) increased slowly on OP, SB and OS but remained low on FS. The density of total bacteria on OP, SB and OS was one order of magnitude higher than that on FS, and the density of zooplankton on SB and OS was significantly higher than that on FS or OP(P<0.05). The improved water quality and increased density of bacteria and zooplankton on SB and OS may have had a synergistic effect on shrimp culture, improving its growth performance(high survival rate and yield and low feed conversion rate). SB and OS were more effective for improving the growth performance of intensively cultured L. vannamei without water change than OP and FS. To our knowledge, this study presents the first evidence regarding the effect of different bottom substrates on intensive shrimp culture.

A Unit Study of Externality of Shrimp Farming on Provisioning Services (Paddy Farming)

Externality;the term can define as a positive or negative impact from either production or consumption of goods or services.Services provided by particular location have very specific dependency on spatial characteristics of that region.A region’s distinct characteristics make it ecologically unique from other such regions.Ecosystem services are offered by these regions thus differ according to these unique ecological features.In this particular study,artificially imposed expansion of coastal shrimp farming towards the inland and its impact over paddy cultivation have been addressed.Optimization of the extent of this manipulative coastal expansion has been supported by little modification of a previously described model.Here the investment prediction for both shrimp and paddy farming has been investigated by calculating net present value(NPV).Shrimp farming has very specific externality on local ecosystem services.In this particular case,some contradictory results are presented and with respect to positive or negative externality;but the externalities are strong.NPV results indicate that there is no long-term profitability in case of shrimp farming.Hence,an overall externality of shrimp farming has been described in context of this study.

Effect of polyculture of shrimp with fish on luminous bacterial growth in grow-out pond water and sediment

Objective:To study the distribution of marine luminous bacteria in shrimp culture systems of West Bengal and the effect of polyculture of shrimp with fish to reduce luminous bacteria.Methods:Luminous bacterial counts were enumerated by spread plating on seawater complex agar from shrimp grow-out pond water and pond sediment samples of West Bengal,India.Results:About 31.16%and 51.44%of pond sediment and pond water samples respectively had detectable levels of luminous bacteria.It was noticed that in normal ponds a shift happened in bacterial profile of water from the day of flooding up to 60 d,with the dominance of luminous bacteria among vibrios,reaching counts 10^(4) cells/mL or more.While in diseased ponds,luminous bacterial abundance within the ponds was noticed in the first 6 weeks of culture.Marked reduction in luminous bacterial counts of water and sediment was observed through out the culture period in polyculture ponds compared to monoculture ponds.There was no incidence of white spot syndrome viral disease and luminous vibriosis in both controlled and experimental ponds.Conclusions:The results suggest vigilant monitoring of ponds for luminous bacteria abundance and polyculture of shrimp with fish in ecofriendly sustainable aquaculture can reduce the impact of shrimp disease outbreak.

Assessment of nitrogen and sulphur cycle bacteria and shrimp production in ponds treated with biological products

Objective:To study the influence of biological products on the levels of nitrogen and sulphur cycle bacteria in shrimp culture systems of West Bengal,India.Methods:The pond water and sediment samples were analyzed for physico-chemical parameters as per standard methods.The bacteria involved in ammonification,nitrification,denitrification,sulphate reduction and sulphur oxidation were enumerated by most probable number technique.Results:The semi-intensive and modified extensive shrimp farms used a variety of biological products during various stages of production.No biological products were used in traditional farms.The water and sediment samples of modified extensive system recorded significantly higher mean heterotrophic bacterial counts.The counts of ammonia,nitrite and sulphur oxidizers,and nitrate and sulphate reducers varied among the systems.The cycling of nitrogen and sulphur appeared to be affected with the intensification of culture practices.Conclusions:The application of biological products in certain systems helped to maintain the bacteria involved in nitrogen and sulphur cycles and safe levels of ammonia,nitrite and nitrate.An assessment of these metabolically active bacteria in shrimp culture ponds and the application of right kind microbial products would help ameliorate the organic pollution in shrimp aquaculture.