Assessment of standard aeration efficiency of different aerators and its relation to the overall economics in shrimp culture

Aerators are essential for maintaining the dissolved oxygen level in shrimp culture operations. Many types of aerators are promoted as suitable for shrimp culture, but their comparative efficiencies and water circulation patterns are least understood. The aerators viz, modified paddlewheel, Scorpion jet, Venture jet, Wavesurge were evaluated to compare the standard aeration efficiency at different saline conditions with the commonly used paddle wheel. The modified paddlewheel had the highest mean aeration efficiency of 2.018 kg O₂/ kWh at 35‰, followed by the paddlewheel with 1.434 kg O₂/ kWh at 20‰ water salinity. Compared to this, the Scorpion jet and the Wavesurge have shown the highest aeration efficiency of 0.667 and 0.412 kg O₂/ kWh at 20 and 35‰ water salinities, respectively, whereas the Venture jet has given only. The aerator's performance was better at medium water salinities (20 and 35‰) than low (5‰) or high saline (50‰) conditions. In addition to aeration, the paddlewheel aerator has given the maximum water circulation speed 3 ft/sec and coverage distance of 24 m. The cost economics were derived by keeping all other expenses constant except aeration associated costs. The internal rate of returns in shrimp culture with a modified paddle wheel was 127 % compared to the commonly used paddle wheel (120 %). However, the scorpion and wavesurge aerators have shown returns of 47 % and 27 % respectively across the salinities. The selection and sizing of aerators based on the biomass and efficiency of the aeration systems can make considerable headway in decreasing the cost of production and energy use.     

Selection of aerators for intensive aquacultural pond

Aeration cost is the third largest cost in intensive aquaculture system after post larvae and feed cost representing about 15% of total production cost. Therefore, selection of aerators plays a major role in maximizing the profit in such system. Over the years, various types of aerators have been developed specifically to enhance the production of aquatic species. The performances of these aerators are generally compared in terms of standard aeration efficiency. However, suitability of a particular aerator at different pond sizes and water quality conditions can best be determined in terms of aeration cost per unit time of operation. In the present study, economic performance of five different aeration systems – circular stepped cascade (CSC), pooled circular stepped cascade (PCSC), 1-hp paddle wheel, 2-hp paddle wheel and propeller aspirator pump were evaluated and compared at different pond sizes, initial DO concentrations of pond and operating hours of aerators; assuming a typical Indian major carp (IMC) culture with commonly practiced stocking density and feeding. Both CSC and PCSC aerators were found to be suitable for pond size less than 1000 m³. However, for pond sizes more than 5000 m³, 1-hp paddle wheel and 2-hp paddle wheel aerators were found to be efficient.     

Water circulation induced by mechanical aerators in a rectangular vessel for shrimp aquaculture

A water streamer was designed for the purpose of enhancing cost-efficient circulation between the water surface and bottom of shrimp aquaculture ponds. We took direct measurements of the water current field induced by the designed aerator in a large rectangular reservoir of dimensions (L)50 × (W)19 × (D)1.3 m³ and compared the results with those of a standard Taiwanese paddle-wheel aerator. Vertical circulation between the surface and the bottom induced by the paddle wheel aerator was less than that by the designed aerator. Furthermore, the paddle-wheel aerator consumed more electric power than the designed aerator. The structures of water current induced by the two aerators are elucidated, and the advantages and disadvantages of the aerators are discussed.Auxiliary employment of the designed aerators may contribute to delivery of high DO water throughout the pond, which is more efficient than a paddle wheel aerator.     

增氧机池塘增氧效果试验的研究

研究不同型式的增氧机性能,可使生产者根据不同养殖对象与模式针对溶氧的需求,选择配置合适的增氧方式。通过对使用最为广泛的叶轮式、水车式、射流式和曝气式增氧机产品性能的池塘实效试验,分析比较各类增氧机性能、工作特性和适用范围。结果表明,养殖水体溶解氧主要来自浮游植物的光合作用;叶轮式、水车式和射流式增氧机应用于服务水域,其增氧能力远远不能满足该水域养殖鱼类的氧需求,但可满足养殖鱼类的应急氧需求;曝气式增氧机因没有应急增氧作用和水体搅拌能力而不适合四大家鱼等常规鱼种的养殖需要。     

微孔曝气式增氧机的性能及应用效果

为研究微孔曝气增氧机的增氧性能和池塘应用效果,按照标准规定的方法进行了增氧性能的试验和不同水深对增氧性能影响的试验,并在池塘中进行应用效果的试验。结果显示:微孔曝气式增氧机具有比叶轮式增氧机等增氧机更强的增氧能力,但不同配置的机型,增氧能力随配套功率和曝气管长度的增加而增强,动力效率则呈明显下降趋势;增加曝气管布置深度可以提高增氧性能,安装深度从2 m增加到4 m,增氧能力增加285%,动力效率增加207%,与其它养殖池塘机械增氧设备相比,池塘水体越深,微孔曝气式增气机的增氧优势越明显。目前,池塘采用微孔曝气式增氧机的配置方式不具优势,需要改进提升。     

Engineering considerations for water circulation in crawfish ponds with paddlewheel aerators

Engineering considerations for paddlewheel aeration in vegetated shallow water ponds for the production of procambarid crawfish is necessary to ensure cost-effective application. Three experimental ponds (approximately 2 ha each) were planted with rice in August as forage for the resident pond population of red swamp crawfish, Procambarus clarkii, and flooded in October. Two 2.2 kW (3 hp), single-phase electric motor (110 V_ac) paddlewheel aerators were placed in each pond. The aerator rotors were 160-cm long and 95-cm in diameter. The aerator rotor had 36 paddles with half the paddles 27.3-cm long and half 34.9-cm long. Rotor speed was set at 83 rpm and operated at three paddle submergence settings: 7.6, 12.7, and 17.8 cm below the water surface. Over a 20-week period between November and April, channel velocity, head difference, and aerator amperage was measured for both one and two aerators in operation in each pond. Results indicated that circulation of oxygenated water from the aerators can be accomplished as efficiently with a single aerator set at a lower paddle depth (7.6-cm) compared to operating two aerators set at a greater paddle depth (12.7 or 17.8-cm). However, based on the apparent efficiency of the aerators and the calculated channel roughness coefficients values obtained from the channel velocities, paddlewheel aerators are an inefficient option for circulating the pond water especially when rice foliage dominants the total vegetative biomass of the pond.     

Aerator energy use in shrimp farming and means for improvement

Estimates of aeration energy use in shrimp farming varied from 11.4 to 41.6 GJ/t shrimp (average = 19.8 GJ/t). Several opportunities for reducing energy use in aeration are available. Many farms adopt an excessive yield to installed aeration capacity ratio. Moreover, the proportion of installed aerator capacity in use and duration of aerator operation per day are often more than necessary during the initial two‐thirds of grow‐out, because adjustment is not made for the quantity of shrimp biomass. Farm‐made, long‐arm aerators used in Asia have several features leading to energy inefficiency and could be replaced by more efficient factory‐made, long‐arm aerators. Asian aquaculture aerator manufacturers should redesign aerators to include design features shown in research to improve efficiency. Dissolved oxygen concentration monitoring essential for verification of aeration performance is seldom performed by shrimp farmers. With good aeration technique, energy use for aeration should not exceed 10–15 GJ/t shrimp.     

池塘养殖中不同机械增氧技术的组合及效果验证

为解决河南中牟县万滩镇养殖池塘机械增氧技术单一的问题,通过试验研究微孔式、水车式、涌浪式等几种增氧机的性能及使用方式,以达到提升增氧效果和提高养殖效益的目的。结果表明,该地区池塘溶氧含量高而利用率低,养殖户传统增氧方法不当。适宜增氧方式为:涌浪式增氧机适合在晴天下午使用3~6 h,可有效提升周边20 m范围内底层水体的溶氧水平;投食前后半小时开启和关闭微孔式、水车式增氧机,可提升投食期间投饵区溶氧水平1~2 mg/L,保证鱼群的进食效果;夜间搭配使用微孔式和低功率叶轮式增氧机增氧,可使微孔区域底层水体溶氧比不增氧状态高出1 mg/L以上。     

The effects of salinity on reproductive development and egg and larvae survival in the spotted scat Scatophagus argus under controlled conditions

In the present study, we report the first successful instance of controlled reproduction in Scatophagus argus, which has recently emerged as a new aquaculture resource. The controlled reproduction process for S. argus was optimized with regard to salinity acclimation. Gonadal maturation was affected by salinity in both sexes. Levels of plasma 17β‐estradiol (E₂) and 11‐ketotestosterone (11‐kT) were salinity dependent and increased significantly with the duration of acclimation. Plasma levels of gonadal steroids were higher in fish held at 25‰ salinity. The highest gonadosomatic indices (GSI), 15.1 ± 1.6 in the female and 6.4 ± 1.2 in the male, were also observed at 25‰ salinity. Nevertheless, the optimal salinity for S. argus embryonic development and larval culture was 15‰. Thus, the salinity requirement for gonadal maturation and early development are quite different. The use of advanced reproductive technologies combining salinity acclimation and stimulation of luteinizing hormone‐releasing hormone analog (LHRH‐A₂) resulted in a fertilization rate of 83.2%–91.3% and embryonic survival rates of over 90%. Embryos of S. argus at the 2‐cell, blastula, gastrula and pharyngula stages were observed. Most embryos hatched after 21.0 hr of incubation at 28.0 ± 1.0°C. The development of larvae into juveniles was completed at 40–45 days posthatch (dph). In this study, we provide information about the controlled reproduction of S. argus and identify the optimal environmental parameters for S. argus embryonic and larval culture, with the aim of developing reliable reproductive techniques for its mass production.     

移动式太阳能增氧机的改进设计与试验

为进一步提高移动式太阳能增氧机的使用效率、降低开发成本,采用Solidworks软件对原型机进行了改进设计及性能测试。通过对运动控制系统的简化和采用非接触式换向的水面行走机构,使得来回行走更加灵敏。性能测试结果显示,改进后的移动式太阳能增氧机,当光照度为17 000 Lx,转速可达到34 r/min。光照度越强,叶轮转动越快,其增氧效率也越高。在输入电压24 V时,选用8.2 kΩ和2 kΩ电阻进行分压,可以使控制电压达到4.7 V。对光敏传感器进行的优化结果表明,选用4.2 kΩ光敏阻值,在低光照强度下能够达到最低20 r/min的转速要求,遥控距离可达到45 m,平均运行时间可达6 h/d左右。电气控制系统采用单元模块,以及更加便捷的水面行走机构,不仅实现了原型机的全部控制要求,还降低了材料成本费用。结果表明,改进后的增氧机性能稳定可靠,适于在池塘养殖中推广。     

Design Characteristics of Spiral Aerator

In this study, the performance of a spiral aerator, a modified design of the paddlewheel aerator, was evaluated to determine its applicability in aquaculture ponds. The aeration characteristics of the spiral aerator were determined by conducting aeration experiments in a cement concrete tank of dimension 5 × 5 × 1.5 m. Nondimensional numbers related to oxygen transfer (E) and power consumption (Ne) were proposed and expressed as functions of geometric (number of handles per shaft, n) and dynamic (Froude and Reynolds number) parameters. Simulation equations for oxygen transfer and power consumption based on the Froude criterion were developed. The maximum brake power standard aeration efficiency was achieved at n = 13. Finally, an economic analysis was performed assuming a typical Indian major carp culture pond to determine the optimum rotational speed of the aerator at different pond volumes and dissolved oxygen concentration present in the pond at which the aeration cost is minimized. The results showed that the least aeration cost is achievable when rotational speed of the spiral aerator is only 70 rpm for pond volumes up to 700 m³ and from 120 to 220 rpm for pond volumes exceeding 700 m³.     

Alteration of the haemocyte parameters,expression of immune‐related and neurohormone bursicon genes of giant river prawn Macrobrachium rosenbergii (de Man) in the response to salinity stress and ammonia stress

We examined the effects of salinity stress and ammonia stress on alteration of the haemocyte count, phenoloxidase activity, expressions of immune‐related genes including prophenoloxidase (proPO), crustin, heat shock protein 70 (HSP70), and expressions of stress‐responsive neurohormone (Bur‐α and Bur‐β) in the thoracic and abdominal ganglia of giant river prawn Macrobrachium. These parameters of prawn that subjected to salinity stress (transferred from 0‰ to 5‰ and 10‰), and subjected to ammonia‐nitrogen (ammonia‐N) stress (transferred from 0 to 0.262 mg/L and 0.786 mg/L) were examined after 0, 3, 6, 24, 72 and 168 hr respectively. During the initial period of 3, 6 and 24 hr, granulocyte haemocyte (granular and semi‐granular hemocyte) count and PO activity significantly decreased, while expressions of Bur‐α and Bur‐β significantly increased. After 24 hr, granulocyte haemocyte count and PO activity significantly increased, whereas expressions of Bur‐α and Bur‐β significantly decreased. The expressions of proPO, crustin and HSP70 were significantly downregulated in the prawn that subjected to salinity stress and ammonia‐N stress at all time periods of 3–168 hr. In conclusion, changes in the granulocyte haemocyte count of M. rosenbergii following salinity stress and ammonia‐N stress are closely associated with the changes of Bur‐α and Bur‐β expressions.     

An evaluation of three paddlewheel aerators used for emergency aeration of channel catfish ponds

Oxygen transfer rate, power requirement and fuel consumption were determined for three paddlewheel aerators used for emergency aeration of channel catfish ponds. The power requirement of the tractor-powered units was directly related to the diameter of the paddlewheel drum and the paddle immersion depth. Oxygen transfer rates ranged from 6·9 to 41 kg h^?1 and increased linearly with the power requirement. The largest paddlewheel aerator, operated at the maximum paddle depth, produced the highest oxygen transfer rate (41 kg h^?1). Oxygen transfer efficiencies ranged from 1·29 to 1·97 kg kWh^?1.     

Estimation of Oxygen Transfer Rates for Mechanical Aerators in Brackishwater Aquaculture Ponds

Oxygen transfer rates for mechanical aerators are usually determined by standard aeration tests conducted in concrete tanks. Results from standard tests are then extrapolated to field application of the aerators in aquaculture ponds, but these extrapolations have not been verified. In this study, oxygen transfer rates were estimated for propeller-aspirator-pump aerators deployed in brackish water aquaculture ponds under normal pond conditions. Estimation was accomplished by fitting the Whole Pond Respiration Diffusion (WPRD) model to nighttime observations of dissolved oxygen concentration for ponds in which artificial aeration had been initiated during the night. Application of this new technique revealed that oxygen transfer rate determined from a standard aeration test was similar to that estimated from trials in aquaculture ponds. Preliminary results suggest that oxygen transfer rates were higher when the aerator was placed in the deep end of the ponds than when the aerator was situated in the shallow end. Aeration efficiencies ranged from 1.45 to 1.8 kg O ₂ per kW-hour.     

Author index

Oxygen-transfer rates (tap water, 0 mg/l dissolved oxygen, 20°C) for four tractorpowered emergency aerators tested in a 820-m³ pond were: blower-fan aerator, 12.2 kg O₂/h; Crisafulli^® pump and sprayer, 12.3 kg O₂/h; Airmaster^® aerator (centrifugal pump and sprayer), 21.3 kg O₂/h; paddlewheel aerator, 26.3 kg O₂/h. Times required for aerators to homogeneously mix salt in a 6000-m³ pond were: blower-fan aerator, 96 min; Crisafulli pump and sprayer, 94 min; paddlewheel aerator, 53 min; and Airmaster aerator, 38 min. The Airmaster aerator and the paddlewheel aerator did not differ in their abilities to transfer oxygen and circulate pond water (P > 0.05); they were both superior to the blower-fan aerator and the Crisafulli pump and sprayer (P < 0.01).     

Vertical Water Circulation Capabilities of an Electric Paddle Wheel Aerator and Dissolved Oxygen Loss Due to Daytime Aeration

ABSTRACT

Vertical water circulation by the paddle wheel aerator was determined by measuring dissolved oxygen profiles in a 3.6-m deep watershed pond during daylight hours, using aerated and non-aerated treatments. The paddle wheel aerator circulated the well-oxygenated surface water to the pond bottom, producing a uniform dissolved oxygen profile in the aerated treatment, while the non-aerated treatment maintained high dissolved oxygen concentrations near the surface with low dissolved oxygen concentrations near the pond bottom. The aerated treatment contained 35.6% less dissolved oxygen than the non-aerated treatment after four hours as a result of operating the aerator during the daytime. The paddle wheel aerator, with a shallow (10 cm) paddle immersion, is effective in vertically circulating water in deeper ponds. However, substantial loss of dissolved oxygen may result from operating the aerator on days with high rates of photosynthesis.     

Impact of salinity changes on growth,oxygen consumption and expression pattern of selected candidate genes in the orange mud crab (Scylla olivacea)

Change in environmental salinity level is a major limiting factor for the aquaculture productivity because it imposes severe stress on organisms that in turn retards growth. The orange mud crab (Scylla olivacea) is an important coastal aquaculture species (farming is practised in 10‰–20‰ salinity levels) in Bangladesh. The present study was conducted to investigate the changes in growth, O₂ consumption and mRNA expression levels of five selected genes in the orange mud crab (S. olivacea) exposed to three different experimental salinity levels (0‰, 10‰ and 20‰) for three months. Crabs reared at 10‰ and 20‰, showed significantly higher (p < .05) growth performance and expression of growth regulatory genes (Actin and α‐amylase). The highest levels (p < .05) of O₂ consumption and expression of ion regulatory genes (Na⁺‐K⁺‐ATPase, V‐type H⁺‐ATPase and Diuretic Hormone) were obtained at 0‰. Moderate levels of growth and expression of selected candidate genes were observed at 10‰ treatment while the highest levels of growth and gene expression were obtained at 20‰ (control salinity). Strong interactions were observed between growth performance and expression of growth genes (R² = 0.81–0.91), and rate of O₂ consumption and expression of ion regulatory genes (R² = 0.83–0.93), implying that the selected genes are important candidates for growth and ionic balance in S. olivacea. Growth performance was found to be very low at 0‰ initially, after 30 days crabs showed better growth performance at this salinity level. It is thus inferred that orange mud crab individuals might require 3–5 days for acclimation to salinity stress but it can take at least 30 days for acclimation to regular growth. Results indicate that with proper acclimation, the orange mud crab (Scylla olivacea) can be farmed at low salinity conditions and possibly in freshwater condition.     

Salinity a significant environmental factor for Vibrio harveyi virulence in Fenneropenaeus indicus

The effect of ambient salinity on the haemolymph variables of Fenneropenaeus indicus and its susceptibility to Vibrio harveyi infection under salinity stress has been studied. Adult shrimps were acclimated to 5‰ (hypo osmotic), 25‰ (iso osmotic) and 35‰ (hyper osmotic) salinity levels and the animals were injected with a mid logarithmic culture of V. harveyi at sub lethal level and haemolymph parameters were analysed. Haemolymph proteins, intracellular superoxide anion production, phenoloxidase (PO), alkaline phosphatase (ALP) and acid phosphatase (ACP) activity were found to be at elevated level both at 5‰ and 35‰ post challenge. The haematological responses showed a progressive increase (P < 0.05) up to post challenge day 5 (PCD 5) followed by a considerable decline at all salinities with the lowest being at 35‰. The alterations in the variables were higher in shrimps held at 5‰. However, the V. harveyi infection was severe in animals held at 35‰. The reduction in the parameters could be correlated with the decrease in survival rate of shrimps at 35‰ with a concurrent increase in V. harveyi at this salinity. Multiple regression analysis revealed that ACP (P < 0.001), haemocyte protein HCP (P < 0.001) and PO (P < 0.05) could explain 91% variability in the shrimp survival. These parameters may be used as effective shrimp health indicators. It is evident from the study that ambient salinity alters the haemolymph variables, modulates the virulence in V. harveyi and makes the shrimps more vulnerable to infection at higher salinity. The virulence of V. harveyi is increased at 35‰ salinity as being evidenced from the high mortality at this salinity. The study emphasizes the importance of salinity as an important environmental factor both in terms of host susceptibility and virulence of the pathogen.     

Diversified aeration facilities for effective aquaculture systems—a comprehensive review

The growing intensive aquaculture system around the world maintains a high stocking density, wherein it is essential to increase and sustain the optimum dissolved oxygen concentration (DO) through the provision of artificial aeration systems. The selection of an aerator is a crucial aspect of aquaculture operations. The selected aerator must be economically efficient and should be able to fulfill the requirement of oxygen supply in the pond water. The present study provides an extensive literature review on the importance of artificial aeration in aquaculture, the standard method of test for performance evaluation of an aerator, various aeration systems and their mechanisms, method to determine the numbers of aerator requirement, comparative studies of different type of aerators, and economic consideration in selection of aerators. In addition, a thorough analysis has been done to suggest the type of aerator that is economically viable and efficient for different pond volumes based on the performance data reported in the reviews. Therefore, this study may help the end-users (fish farmers) to select the best aerator based on their requirements.

     

Effects of salinity level on the survival,growth, feed utilization,carcass composition,haematological and serum biochemical changes of juvenile Meagre (Argyrosomus regius) (Asso, 1801) grown in ground saltwater

A study was performed to examine the effects of salinity on water quality, fish performance, carcass composition and haemato‐biochemical parameters in juvenile meagre, Argyrosomus regius. Fish (5.0 g) were stocked in fibreglass tanks at four salinity levels: 8‰, 16‰, 24‰ and 32‰, and fed a pelleted diet (47/17 protein/lipid) for 56 days. Results indicated that the growth, feed utilization, carcass composition and haemato‐biochemical parameters of meagre gradually improved with the increase in salinity up to 24‰ and then significantly (p ≤ .05) decreased at 32‰. The survival per cent showed a significant decrease when A. regius exposed to 8‰ salinity. An improvement with 32%, 47% and 34.1% of FCR, protein productive value and energy utilization was detected at 24‰ compared with 8‰ salinity respectively. The highest content of protein and the lowest of lipids were recorded in fish carcass at 24‰ compared with the opposite trend at 8‰ salinity. The 24‰ salinity treatment exhibited the highest value of haemoglobin (4.9 g/dl) and the lowest ratio (0.73) of albumin/globulin. The serum total protein, albumin and globulin were significantly higher at 24‰ and 32‰ salinity than those at 8‰ and 16‰ salinity groups. These findings indicate that 24‰ salinity level might be the best for meagre.