室内集约化养虾池以低频率运转水处理系统调控水质效果及氮磷收支

采用低频率运转循环水处理系统(含粗滤器、臭氧仪、气液混合器,蛋白分离器、暗沉淀池等)联用池内设施(微泡曝气增氧机与净水网)开展凡纳滨对虾室内集约化养殖实验。研究了养虾池以水处理系统调控水质效果及氮磷收支。结果表明,养虾水经系统处理后,NO₂-N(53.4%～64.5%)、COD_Mn(53.4%～94.4%)与TAN(31.6%～40.4%)被显著去除,有效改进虾池水质;养殖周期内未换水与用药,虾池主要水化指标均控制在对虾生长安全范围,7号实验池(100 d)与8号对照池(80 d)主要水化指标变化范围:DO分别为 5.07～6.70 mg/L和4.38～6.94 mg/L,TAN 0.248～0.561 mg/L和0.301～0.794 mg/L,NO₂-N 0.019～0.311 mg/L和0.012～0.210 mg/L,COD_Mn 10.88～21.22 mg/L和11.65～23.34 mg/L。7号池对虾生长指数优于8号池(80 d虾病暴发终止),单位水体产量分别为1.398 kg/m²与0.803 kg/m²。氮磷收支估算结果:7号与8号池饲料氮磷分别占总收入:氮93.70%与92.37%,磷98.77%与99.09%;初始水层与虾苗含氮共占总收入6.30%与7.63%,磷共占1.23%与0.91%。总水层(含排污水)氮磷分别占总输出:氮56.45%与59.86%,磷53.26%与55.79%;收获虾体氮磷分别占总输出:氮37.07%与31.94%,磷21.37%与13.11%。7号池饲料转化率较高;池水渗漏与吸附等共损失氮磷分别占总输出:氮7.00%与9.34%,磷25.37%与31.10%。实验结果表明,虾池以低频率运转循环水处理系统联用池内设施可有效控制水质与虾病,具较高饲料转化率。     

Effects of biological water purification grid on microbial community of culture environment and intestine of the shrimp Litopenaeus vannamei

Biological water purification grid (BWPG), a type of biofilm, could increase aquaculture production by improving the growth of shrimp and culture environment. In this study, the microbial community composition and diversity of water, sediment and shrimp intestine were analysed using the Illumina Miseq high‐throughput sequencing technique. Installation of BWPG did not only increase the dissolved oxygen, pH and decreased inorganic nutrients, but also increased shrimp body length by 5.39% and weight by 16.35%. Furthermore, it was found that the microbial community diversity of water and shrimp intestine in test pond with BWPG was higher than that of control pond without BWPG. Cyanobacteria, Bacillus and Lactococcus were enriched in the test pond with BWPG. However, Rhodobacter was mainly identified in the test pond. It thus seems to suggest that the application of BWPG in shrimp culture pond enhanced the microbial species richness, types of species and proportion of beneficial bacteria in culture environment as well as shrimp intestine. The results from this study will therefore provide some scientific basis for the improvement and development of shrimp aquaculture.     

Effect of water exchange on effluent and sediment characteristics and on partial nitrogen budget in semi-intensive shrimp ponds in New Caledonia

An experiment was conducted in six earthen ponds with 20 shrimps m^?2Litopenaeus stylirostris (Stimpson) during the warm season in New Caledonia to study the dynamics of wastes in relation with water exchange rate (WER). The nitrogen budget was established, taking into account the different forms of nitrogen in the water, sediment, feed and shrimp. Data from a wide range of treatments applied in unreplicated ponds were treated using regression analysis to establish the relationship between WER and partial nitrogen budget, sediment characteristics and shrimp performance. To compare effluent quality between treatments during the season, data were analysed using the non‐parametric sign test. The water outflow was characterized by a decrease in the concentrations of N‐mineral forms (TAN, NO₂^?–NO₃^?), an increase in the concentration of organic soluble and sestonic organic forms (expressed in terms of particulate nitrogen, particulate organic carbon, chlorophyll a) compared with the water inflow. Increasing WER increased the amount of exported wastes and mainly in the organic forms and TAN can be considered as negligible. The nitrogen budget showed that 19–46% of nitrogen input (feed+water) was exported into the coastal environment. The results showed that the quality of the sediment decreased as WER decreased. The potential negative impact of the developing industry in New Caledonia on the costal environment could be partially reduced in a first step by decreasing WER. However, if applied in the farms, this practice should be linked to a close survey of the evolution of sediment quality.     

PET净水栅对虾池养殖生态环境的影响研究

以PET细丝缠绕成结而形成线性附着基质作为生物净水栅载体材料,在汕头市牛田洋养殖基地设置实验组池塘和对照组池塘(无PET净水栅),于2015年6月至12月定期采集虾池养殖水、浮游植物及对虾样品,测定各项水质指标、浮游植物多样性、对虾生长指标,分析比较PET净水栅对池塘养殖生态环境、凡纳滨对虾(Litopenaeus vannamei)生长情况的影响。结果表明,较养殖初期(6月23日),养殖末期(12月12日)实验池水体氨氮(NH4-N)、硝氮(NO3-N)、亚硝氮(NO2-N)浓度分别下降了68.25%、42.71%、83.51%。浮游植物研究结果表明,对照池和实验池浮游植物平均丰度为5.17×108个·L-1和3.62×108个·L-1,实验池的Shannon-Wiener指数和均匀度指数分别高于对照池8.70%和6.45%(P0.05)。结果表明,实验期间实验池凡纳滨对虾的平均体长和体质量分别高于对照池6.13%和16.67%(P0.01);实验池单位面积饲料用量低于对照池15.44%(P0.01)。     

Effect of stocking density on soil,water quality and nitrogen budget in Penaeus monodon (Fabricius, 1798) culture under zero water exchange system

Soil and water interactions and their influence on growth and production in different densities (SD8 & SD16) under zero water exchange were studied in two successive crops of Penaeus monodon in Tamil Nadu, India during 2007 and 2008. Scraping and tilling during pond preparation increased the mineralization rate than scraping only. During crop, there was no significant difference in soil organic carbon and total nitrogen between the SDs. However, as the crop progressed, organic carbon and total nitrogen content of the soil showed significant difference under both the SDs. Between the SDs, nitrate and phosphate content in water significantly differed, whereas the progress of the crop significantly increased both available and total nutrients. Mass balance of nitrogen indicated that applied feed contributed to 97.4–98.5% of input nitrogen, of which nitrogen in sediment accounted for 16.5–27.3%, nitrogen recovery in shrimp was 34.2–43.6% and the nitrogen lost through denitrification and volatilization varied from 4.7% to 34.7%. Zero water exchange system is highly efficient as nitrogen recovery is higher in shrimp and lower in discharge water. Lack of significant difference in metabolites between the SDs indicates the role of aeration and probiotics in sustaining SD16 cultures.     

Effects of a partitioned aquaculture system on water quality and growth of Penaeus vannamei

The effects of system partition on the water quality were studied using three shrimp ponds (Ts), and each one of the shrimp pond was connected individually with a fish pond by piping and pump. Three other isolated shrimp ponds were designated as the Cs treatment. The results showed that the implementation of the system can improve the water quality in the shrimp ponds. Particulate organic matter (POM), chemical oxygen demand (COD), nitrite nitrogen (NO₂–N) and nitrate nitrogen (NO₃–N) in the Ts were lower than those in the Cs during the experiment, and in some cases, they were significantly lower (p < 0.05). Throughout most of the experimental period, the soluble reactive phosphorus in the Ts treatment were greater than that in the Cs treatment (p < 0.05), and N/P ratio of the water column was lower in the Ts treatment than in the Cs treatment throughout most of the experimental period (p < 0.05). These results indicate that the partitioned system contributed to the stability of water quality and N/P ratio in the water. Vibrio parahaemolyticus was dominant in the third to seventh weeks in Cs, and the dominant condition was found only in seventh week in Ts. The result indicated that system may contribute to the slowing down of the breakout of V. parahaemolyticus in the shrimp pond. According to the redundancy analysis, COD, chlorophyll a and POM were mainly positively related to the dominance index of V. parahaemolyticus, and maybe POM can serve as an indicator to reflect the trend of V. parahaemolyticus.     

Effect of Water Exchange Rate on Waste Production in Semi-Intensive Shrimp Ponds During the Cold Season in New Caledonia

An experiment was conducted in six earthen ponds with 20 shrimp/m² ( Litopenaeus stylirostris ) during the cold season in New Caledonia to determine the effect of water exchange rate on characteristics of effluents and pond sediment. The nitrogen budget was established, taking into account the different forms of nitrogen in the water, sediment, feed, and shrimp. Mean water exchange rates ranged from 10 to 23% per day. Increasing water exchange rate did not cause any significant change in the average quality of the rearing environment (water and sediment) during the whole growout period. However, the results showed that increasing exchange rates boosted primary productivity. Compounds produced by the mineralisation and metabolism of organic matter (feces, uneaten feed) were exported as particulate, rather than soluble matter. The nitrogen budget showed that the amount of exported wastes from the pond into the coastal environment was only 40–50% of nitrogen inputs due to nitrogen accumulation in the pond sediments and/or release to the atmosphere. The highest accumulation of dry material, as well as the highest Δ N (concentration of total N at the end of rearing - concentration of total N before rearing), was observed in ponds with the highest WER.     

Characterization of bacterial community in intestinal and rearing water of Penaeus monodon differing growth performances in outdoor and indoor ponds

Penaeus monodon provides a high‐quality protein source for humanity, and pond cultured shrimp often presents asynchronous growth. Microbial communities are important for the digestion and immunity of shrimp. Therefore, in this study, we investigated the bacterial characteristics of the intestine and rearing water of asynchronously growing P. monodon that were cultured in outdoor and indoor pond respectively. The results showed that the bacterial community of the rearing water was more complex than that of the intestine; the fast‐growing shrimp in the indoor pond had higher intestinal bacterial diversity. Besides, the dominant bacterial composition of the water was more complex than that of the intestinal. Specifically, the abundance of Proteobacteria in the intestine was consistent with the growth performance of shrimp in the outdoor pond, which was exactly the opposite in the indoor pond. At the genus level, two cyanobacteria, Limnothrix and Cyanobium PCC‐6307, were dominant in the indoor and outdoor water respectively. In the outdoor pond, Bacillus was dominant in the slow‐growing shrimp intestines, while Vibrio was dominant in the fast‐growing shrimp. The intestinal microbes of the fast‐growing shrimp had higher proteasome metabolic capacity. These results can provide new insights into microbiome characteristics involved in the asynchronous growth of shrimp.     

强降雨对粤西凡纳滨对虾养殖池塘微生物群落的影响

于强台风"莫拉菲"环流云系带来的持续强降雨天气前后(2009年7月14日和7月28日),对广东省茂名市电白县凡纳滨对虾半集约化养殖土池的水样和泥样进行调查,研究施用微生态制剂和未施用微生态制剂的虾池水体及底泥中的异养细菌、弧菌和芽孢杆菌的变化情况,并利用BIOLOGECO微板对水体和底泥的微生物群落代谢变化进行探讨。结果发现,定期施用微生态制剂的虾池水体和底泥中的细菌数量和微生物群落功能在强降雨前后基本保持稳定;未施用微生态制剂的虾池在强降雨后,水体的弧菌数升高,Simpson指数和McIntosh指数显著降低(P0.05),水体和底泥微生物群落对碳源的利用率变化明显。研究结果表明,与施用微生态制剂的虾池相比较,未施用微生态制剂的虾池在强降雨后,水体及沉积物环境波动变化明显,强降雨对其水域环境产生很大的影响。因此建议在对虾养殖过程中定期施用微生态制剂,并针对恶劣天气采取有效措施,以稳定虾池水体及沉积物的微生物生态。     

Pond Bottom Management at Commercial Shrimp Farms in Chantaburi Province,Thailand

Most shrimp farmers in Chantaburi Province, Thailand, use water jets to dislodge sediment from empty pond bottoms, and wastewater is held for sedimentation before discharge into natural waters. Other pond bottom management practices used by a few farmers are sediment excavation, leave sediment but till entire pond bottom, and no mechanical treatment. All four methods of pond bottom treatment are followed by sun drying for 30 d. Soil organic carbon concentration in ponds following dry‐out seldom exceeded 2%. Although shrimp production in 24 ponds supplied by the same source of water was negatively correlated with increasing soil organic carbon concentration (r = ?0.582), this observation does not confirm a causative relationship. Moreover, in trials conducted at Burapha University, Chantaburi Campus, bottom soil organic matter concentration following dry‐out differed little irrespective of treatment method. Lower soil moisture concentration revealed that dry‐out was more complete with sediment removal than without, but better dry‐out resulted in lower soil pH. Removal of sediment by excavation or flushing is expensive, and natural dry‐out combined with liming and occasional sediment removal should be investigated as a less expensive and more environment‐friendly alternative to removing sediment after each crop.     

Effects of shrimp pond water on phytoplankton: importance of salinity and trophic status of the receiving environment

Aquaculture generates a large load of effluents rich in organic matter and nutrients that may be introduced into the environment. This study aimed to assess in a microcosm experiment, the effect of shrimp pond water mixed with Patos Lagoon estuary water on phytoplankton chlorophyll a and primary production, simulating two salinities. Chlorophyll a, dissolved inorganic nutrients and primary production were measured in two experiments. In Harvest I, salinity of shrimp pond and environment water was similar, and chlorophyll a showed different trends over time, according to the amount of nitrogen available. In Harvest II, with different salinities and high nutrient concentrations in environment water, chlorophyll a levels showed a similar increasing trend over time in all mixtures. Net primary production showed differences among treatments in the first sampling in Harvest I, but not in the second, whereas no differences were observed among treatments in Harvest II. We conclude that shrimp pond effluent can lead to short‐term variations in chlorophyll a and primary production levels, with similar salinities. Salinity differences result in lower chlorophyll a and primary production values than expected according to the nutrient input. Differences in salinity can be an important management strategy to choose the best harvest period.     

Effects of water exchange protocols on water quality,sedimentation rate and production performance of Penaeus monodon in earthen ponds

This study was carried out in farmers' fields to quantify the total water and consumptive water use in grow‐out culture of Penaeus monodon under recommended package of practice with two different water management protocols: T₁, with no water exchange and T₂, with regulated water exchange. Treatment‐wise estimated total water use, was 2.09 and 2.43 ha‐m 122 day^?1, while the computed consumptive water use index (m³ kg^?1 biomass) was 5.35 and 6.02 in T₁ and T₂ respectively. Lower rates of water exchange (T₂) showed significantly improved (P < 0.05) crop performance in terms of performance index (19.75 ± 0.75), production‐size index (74.1 ± 3.4), survival rate (80.13 ± 1.7%) and productivity (2.44 ± 0.08 t) over the zero water exchange. The shrimp pond water quality suitability index (WQSI) infers that regulated water exchange (T₂) improved the overall suitability of water quality for shrimp culture. WQSI up to 90 days of culture ranged between 7.5–9.0 in T₂, needs little management while in the last month of rearing, it was good with moderate management requirements. Treatment‐wise sediment load ranged between 50.4–56.3 m³ t^?1 shrimp biomass. High intensity of water exchange and low apparent feed conversion ratio influenced in lowering the sedimentation rate. Regulated water exchange protocol (T₂) performed well (higher net total water productivity and net consumptive water productivity) against no water exchange (T₁). A higher OV:CC ratio (ratio of the output value to the cost of cultivation) indicated that T₂ had a distinct edge over the T₁ protocol.     

Physical and Chemical Characteristics of Bottom Soil Profiles in Ponds at Auburn, Alabama, USA and a Proposed System for Describing Pond Soil Horizons

Soil cores were taken from each of three, 2-, 23-, and 52-yr-old research ponds (650–1,010 m² area) at Auburn, Alabama. Many physical and chemical variables changed in intensity with increasing depth in cores. Compared to original compacted pond soil, sediment contained more moisture; had lower bulk density (<1.4 g/cm³); possessed higher percentages of silt and clay; had greater porosity, specific surface area, and cation exchange capacity; and contained greater concentrations of organic matter and nutrients. Sediment organic matter was highly decomposed as evidenced by low proportions (5–15%) of carbon and nitrogen associated with the light fraction (soil retained on a 53-μm sieve). Sediment depth at 100-cm water depth increased with pond age (11.7 cm, 28.3 cm, and 48.3 cm in 2-, 23-, and 52-yr-old ponds, respectively), but sediment composition did not change greatly over time. Successive layers in cores were as follows: 1) water near the soil-water interface with a high concentration of solids; 2) high moisture content sediment with dry bulk density <0.3 g/cm³; 3) lower moisture content sediment with bulk density between 0.3 and 0.5–0.7 g/cm³; 4) rapid transition of bulk density from 0.5–0.7 g/cm³ to 1.4 g/cm³; 5) original compacted soil with bulk density of 1.4–1.7 g/cm³. We propose that these five layers be referred to as F (flocculent layer), S (stirred or mixed sediment), M (mature, bulk, un-mixed sediment), T (transitional layer), and P (original, undisturbed pond bottom) horizons, respectively. Superficial, oxidized sediment is termed an S_o horizon, and the reduced part of the S horizon is termed an S_r horizon. The upper part of the T horizon is an MT horizon when it is similar to the M horizon, or a FT horizon when it resembles the P horizon. A system for delineating horizons in pond soil profiles will be valuable in future attempts to classify pond soils.     

Stimulating effects of pond water on digestive enzyme activity in the Pacific white shrimp, Litopenaeus vannamei (Boone)

Crude enzyme extracts were obtained from the digestive glands of Pacific white shrimp, Litopenaeus vannamei (Boone), reared in oligotrophic well water and eutrophic shrimp pond water to compare digestive enzyme activity between the two groups. Specific activities of serine protease, collagenase, amylase, cellulase, lipase and acid phosphatase were significantly higher (P < 0.01) in pond water‐reared shrimp (PW shrimp) than in well water reared‐shrimp (WW shrimp). For most enzymes assayed, specific activity was more than two times higher in PW shrimp, and cellulase activity was over six times higher. In contrast, chitinase activity was significantly higher (P < 0.001) in WW shrimp. Higher specific activity of most digestive enzymes in PW shrimp was probably due to natural productivity in the pond water that served as a source of organic substrates, and this increased activity may contribute to the growth‐enhancing effect of shrimp pond water.     

Toxicity of chlorine to different sizes of black tiger shrimp (Penaeus monodon) in low-salinity shrimp pond water

An experiment was conducted, in a dark room with controlled temperature (27.3–28.4 °C), to determine the acute toxicity of chlorine concentration to black tiger shrimp (Penaeus monodon fabicus) of sizes 0.02 g, 2.75 g, 8.47 g and 23.65 g. Toxicity tests on each of these shrimp sizes were run in triplicate in glass jars under static conditions without media renewal. The concentration of active chlorine that killed 50% of the shrimp of each size after 24‐h exposure (LC₅₀‐24 h) was used as an indicator of acute toxicity. Chlorine concentrations applied in the shrimp toxicity test ranged from 2.0 to 14.5 mg L^?1 in shrimp pond water. As the test water contained total suspended solids of 22.0–85.0 mg L^?1 and total ammonia nitrogen of 0.18–0.40 mg L^?1, the resultant concentrations of combined residual chlorine ranged from 0.6 to 3.5 mg L^?1, which were the effective doses causing shrimp mortality. The test results showed that 24‐h LC₅₀ for average shrimp size at 0.02, 2.75, 8.47 and 23.65 g occurred in water containing combined residual chlorine at a concentration of 0.91, 1.39, 1.74 and 1.98 mg L^?1, for which the original application doses were 6.96, 2.05 11.50 and 13.34 mg L^?1 respectively.     

The effects of sediment redox potential and stocking density on Pacific white shrimp Litopenaeus vannamei production performance and white spot syndrome virus resistance

Redox potential represents the intensity of anaerobic condition in the pond sediment, which may affect the dominant microbial transformations of substances, the toxins production, mineral solubility, as well as the water quality in the sediment–water interface inhabited by the shrimp. This study evaluates the effect of sediment redox potential in conjunction with stocking density on shrimp production performance, immune response and resistance against white spot syndrome virus (WSSV) infection. A completely randomized two factors experimental design was applied with three different sediment redox potential, i.e. ?65, ?108 and ?06 mV, and two shrimp densities, i.e. low (60 shrimp m^?2) and high (120 shrimp m^?2). Shrimp juveniles with an initial mean body weight of 5.32 ± 0.22 g were maintained in semi‐outdoor fibre tanks (270 L in capacity) for 35 days of experimental periods. At the bottom of each tank, 5‐cm deep soil substrate with different redox potential was added according to the treatments. The survival and biomass production were significantly reduced at ?206 mV sediment redox potential, regardless of stocking density. Highly negative sediment redox potential (?206 mV) and higher stocking density significantly reduced total haemocyte counts and phenoloxydase activity, and shrimp resistance to WSSV infection. We recommend to maintain the redox potential of pond sediment at a level of more than ?206 mV.     

菲律宾蛤仔垦区育苗技术优化及其对池塘理化环境、浮游植物和稚贝生长的影响

为改进菲律宾蛤仔垦区育苗技术,设置一口池塘(A)培育高密度浮游植物并定期添加至育苗池(B),未添加藻类育苗池(C)作为对照,比较了A、B、C以及邻近自然海区(D)的水体、沉积物、浮游植物状况和池塘B、C中稚贝生长情况。结果显示,池塘A、B、C之间水质和沉积物各指标无显著性差异,但三者水体中盐度、pH、溶解氧、氨氮、硝酸盐氮、活性磷酸盐和沉积物中有机碳、硫化物与自然海区D差异显著;浮游植物密度ABCD,但仅A、D间差异显著;池塘B稚贝壳长和密度均显著大于池塘C。这表明垦区与自然海区环境差异大,而育苗期间通过外源补充藻类能提高稚贝的生长率和成活率,进而提高菲律宾蛤仔垦区育苗成功率。     

Effects of water exchange and abiotic factors on zooplankton and epibenthic fauna in shrimp ponds

Assemblages of zooplankton and epibenthic invertebrates were collected from a commercial Penaeus monodon (Fabricius) pond at fortnightly intervals over an entire grow‐out season. The pond inlet and outlet water were also sampled intensively over three 1‐week periods throughout the season. Before stocking the ponds with shrimp postlarvae, copepods dominated the zooplankton. Immediately after the ponds were stocked, there was a rapid decline in zooplankton numbers, particularly the dominant larger copepods, suggesting heavy predation by shrimp postlarvae. For the rest of the season, barnacle nauplii were the dominant zooplankton component in the pond. Pond water exchanges had little detectable influence on the composition or density of the zooplankton assemblage. Instead, the dominance of barnacle nauplii appeared to have been maintained by steady recruitment due to barnacle reproduction in the pond. While changes in the biomass of pond zooplankton were not correlated with physico‐chemical characteristics, changes in density were positively correlated with temperature, and negatively correlated with pH, dissolved oxygen and secchi disc readings. Epibenthic faunal density peaked at the end of the season, while the biomass peaked during the middle part of the season. Sergestids (Acetes sibogae Hansen) were the most abundant epibenthic taxa. No correlations were found between physico‐chemical parameters and epibenthic fauna biomass or density. Abundances of epibenthic fauna were not related to zooplankton densities, suggesting that trophic interactions between these assemblages is not important. No Acetes were captured in samples of outlet water, and only on a single occasion were large numbers captured in the inlet water; after this, there was a notable increase in the number of Acetes in the pond. This evidence, together with the lack of an increase in the size of Acetes during the season, suggests that water exchange is an important but unpredictable source of recruitment of epibenthic fauna into the pond. The results emphasize the benefits of ensuring that appropriate zooplankton assemblages have been introduced into the ponds, when they are filled, to support the shrimp immediately after stocking. This will depend on the initial inoculum and may be difficult to manipulate with water exchanges once established. Assemblages of epibenthic fauna appear more likely to change with exchanges and may need to be monitored across the season, particularly if their presence reduces production through adverse impacts such as competition with postlarvae, introduction of disease or deteriorated water quality.     

The effectiveness of a commercial microbial product in poorly prepared tiger shrimp, Penaeus monodon (Fabricius), ponds

The efficacy of a commercial microbial product was tested in commercial tiger shrimp, Penaeus monodon (Fabricius), ponds for one culture period in Kuala Selangor, Malaysia. Four ponds with replicates for treatment and control were used. The pond bottom was dried but the organic sludge was not removed as normally practised in pond preparation. The ponds were stocked with 15 post‐larvae at the rate of 31.m^?2. Physical, chemical and biological parameters of the pond were analysed every 2 weeks during the culture period. Water quality parameters remained within the optimum range for shrimp culture except for ammonia‐nitrogen being significantly higher in control ponds and silica in treated ponds. Benthic organisms were not found in any of the ponds. The average counts of different bacteria were not significantly higher in treated ponds than control. Because of poor health, the shrimp were harvested earlier (72 days) than the usual 120 days. An average of 875.60 ± 67.00 kg shrimp ha^?1 was obtained in treated ponds with a feed conversion ratio (FCR) of 1.57 ± 0.10 and survival rate of 42.35 ± 5.37% compared with 719.50 ± 130.94 kg shrimp ha^?1, 2.99 ± 0.70 and 21.25 ± 3.26%, respectively, in control ponds. Neither the microbial product nor the frequent water exchange was effective in overcoming the problems caused by the poor pond bottom.     

Liming and Fertilization of Brackishwater Shrimp Ponds

Agricultural limestone and burnt lime are applied either to the water during shrimp production or to pond bottoms between shrimp crops. However, unless the total alkalinity and total hardness of pond water is below 50 mg/L as equivalent CaC0₃ or the pond soils are acidic (pH < 7), liming is of little or no value. The use of burnt lime should be avoided because this material can cause high pH in water and soil. Chemical fertilizers or manures are used to fertilize brackishwater ponds. Fertilization programs for brackishwater ponds usually require more nitrogen (N) than those for freshwater ponds. Phosphorus (P) fertilization is important both in brackishwater and freshwater ponds. Because water is exchanged often in brackishwater ponds, fertilizer should be applied in small doses and at frequent intervals. Most managers of brackishwater ponds prefer a large proportion of diatoms in the phytoplankton community. An N:P application ratio of 20:l in ponds favors diatoms; in fiberglass tanks with water of low silica concentration, fertilization with silica encouraged an abundance of diatoms.