Economic Assessment of Alternative Aquaculture Aeration Strategies

Oxygen depletion is a serious problem for the catfish industry, especially as producers attempt to increase their production intensity. Aeration, either emergency or continuous, is the most common method used to address oxygen depletion.
A risk-programming model using Target MOTAD methodology was developed to study the aquacultural producer's aeration decision-making process. Effects of stocking rate, aeration yield response and availability of labor, capital and electricity on the selection of aeration strategy were analyzed.
Continuous aeration with electric paddlewheels was most often selected as the best aeration strategy. However, as farmers become increasingly concerned with financial risk, they apply continuous aeration with pump sprayers first, then no aeration and lastly emergency aeration with tractor-powered paddlewheels. Emergency aeration was only used when: 1) electricity was not available and the producer desired a highly conservative financial strategy, and 2) the relative efficiency of continuous aeration in the field was dramatically reduced from experimental results.     

Efficiency of biofloc technology in suspended growth reactors treating aquacultural solid under intermittent aeration

Aquacultural solid waste from a recirculation aquaculture system was used as a substrate to produce heterotrophic bacteria in suspended growth reactors. The efficiency of nitrogen recycling under intermittent aeration (IA, 0.5-h aeration/0.5-h non aeration) and continuous aeration (CA) strategy was investigated. The nitrogen dynamics, biochemical composition of biofloc and efficiency of nitrification/denitrification/ammonium assimilation of biofloc were determined. No significant differences were observed in the nitrogen recycling rate, crude protein and polysaccharides contents of biofloc between the IA and CA reactors. The energy used for intermittent aeration was almost one half of that for continuous aeration. IA strategy (0.5-h aeration/0.5-h non aeration) appears to be more effective to produce biofloc in aquaculture solid waste in reactors than CA strategy.     

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。     

Paddlewheel Effects on Shrimp Growth, Production and Crop Value in Commercial Earthen Ponds

The effects of continuous paddlewheel operation on shrimp growth, yield and crop value were studied in Hawaii. Six 0.4 ha earthen ponds were stocked with Penaeus vannamei at 25 postlarvae/m². Three ponds served as controls with no mechanical aeration or mixing. Each of the other three ponds had two 1 hp paddlewheel aerators (3.7 kw/ha) running continuously throughout the five month trial (29 April-8 October 1986). All other management factors were applied uniformly.
Daily water temperature and use were significantly different between treatments. Paddlewheel ponds had lower water temperatures (28.3 vs. 28.5 C) and lower water use (0.8% exchange per day vs. 2.2% exchange per day) than control ponds.
Faster shrimp growth in paddlewheel ponds was evident in week 8. At week 14, mean shrimp body weights and growth rates were significantly greater. Shrimp at harvest were 21.2 ± 2.6 g in paddlewheel ponds versus 15.3 ± 2.6 g in control ponds. Mean shrimp production was 2,852 ± 222 kg/ha in paddlewheel ponds compared to only 2,061 ± 558 kg/ha in controls. Mean crop value was $13,719 per pond per crop for paddlewheel ponds versus $9,111 for control ponds. Hence, paddlewheels afforded an increase of 42% in net crop value after subtracting purchase and operating costs.     

WATER CIRCULATION—AN ALTERNATIVE TO EMERGENCY AERATION

A management system, replacing emergency aeration practices with gentle pond circulation, has been employed over an entire catfish growing season. Five waterblenders were used to provide pond circulation for a 1.42 ha catfish pond stocked at a density of nearly 10,000 finger-lings/ha. Pond water circulation during the daytime hours mixed oxygen-rich surface waters with the deeper oxygen-poor waters. The waterblending operation continued long enough after dark to decrease the thermal gradients, so that the diurnal temperature change provided top-to-bottom mixing on most nights during the season. Comparisons of yield data, power requirements, and oxygen and temperature profiles show the advantages of the pond receiving water circulation over a neighboring pond that was aerated only on an emergency basis. Comparisons of waterblending with recent aeration studies of other investigators show an order of magnitude reduction in energy uses.     

Financial risk analysis of three aeration regimes in catfish cage culture

Abstract

This study analysed the benefits and costs of three airlift aeration regimes — continuous (24 hr), partial (9 hr/night plus emergencies), and no aeration — for channel catfish in cages. Data from four field studies included four dependent variables based on size at harvest, and six independent variables. Four regression models were fit with a modified Cobb‐Douglas production function in a Seemingly Unrelated Regression system. Yield projections from the production function were then used in a stochastic economic model with prices and variable costs expressed as triangular distributions. Results indicated that none of the aeration methods was preferred to the others by either first‐ or second‐degree stochastic dominance criteria, although partial aeration was the risk‐neutral choice. A power analysis was used to demonstrate that an impractical number of replicates would be needed to detect a difference between partial and continuous aeration that was both economically and statistically significant.     

Economics of risk and uncertainty of alternative water exchange and aeration rates in semi‐intensive shrimp culture systems

Abstract

Reducing water exchange in shrimp aquaculture to minimize discharge of pollutants is a search for sustainability. In desert regions, like most of northwest Mexico, low water exchange must be complemented with artificial aeration to compensate for low levels of oxygen in warm and highly saline water. The economic yield of a low‐water‐exchange production system is compared against yield from a typical water‐exchange‐without‐aeration system for Penaeus vannamei culture. The difference between two systems is centered on pumping and aeration rates for a 100 ha semi‐intensive farm in northwest Mexico.

A bioeconomic model was built to compare the systems. Risk analysis is adopted to account for uncertainty of seed price, shrimp growth rate, survival rate, and shrimp prices.

The typical system was slightly more profitable than the low‐water‐exchange, aerated system. The latter used less electricity than the former in all of the three mortality‐rate scenarios. However, the difference in profitability is so small that for practical purposes both production systems provide similar economic yield. For a typical system, the probability of reaching a positive net present value (NPV) is high, therefore under the assumed risks, a 100 ha semi‐intensive shrimp farm in northwest Mexico is a good investment choice.     

Dissolved Oxygen and Aeration in Ictalurid Catfish Aquaculture

Feed‐based production of ictalurid catfish in ponds is the largest aquaculture sector in the USA. Feed has an oxygen demand, and increases carbon dioxide, ammonia nitrogen, and phosphate inputs to ponds. Major sources of oxygen in ponds are phytoplankton photosynthesis and mechanical aeration; the major sink for oxygen is respiration by fish and by microorganisms in the water column and sediment. Dissolved oxygen concentrations decline when respiration exceeds photosynthesis, and the most crucial time for low dissolved oxygen concentration is at night. Mechanical aeration is applied to avoid nighttime dissolved oxygen concentrations from falling below the critical level for catfish of 3 mg/L. Electrically powered paddlewheel aerators are used by most catfish producers. The oxygen‐transfer efficiency of these aerators is known, but calculations of aeration requirement from stocking and feeding rates are not reliable because of variation in phytoplankton abundance and in weather conditions. Dissolved oxygen concentrations must be monitored, and when measurements suggest that nighttime dissolved oxygen concentration will be unacceptably low, tractor‐powered emergency aerators must be operated to supplement dedicated aeration. Dissolved oxygen concentration also is important in hatcheries, and small aeration systems have been developed for hatchery application.     

Effect of Water Exchange and Mechanical Aeration on Grow‐out of the Amazon River Prawn in Ponds

Exchange and aeration of pond water are common practices in semi‐intensive freshwater prawn culture, but there is lack of scientifically based information on the results. We evaluated the effects of water flow through the ponds and mechanical aeration in semi‐intensive cultures of Macrobrachium amazonicum. A total of 40 juveniles/m² were stocked for 4 mo in 12 earthen ponds. Four randomly assigned treatments were applied: no aeration + no water exchange (NN), diurnal aeration + no water exchange (DA), nocturnal aeration + no water exchange (NA), and continuous water flow (CF). Temperature, pH, total suspended solids, and soluble orthophosphate in the water column did not differ among treatments. Dissolved oxygen (DO) concentrations in ponds with nocturnal aeration were significantly higher than in other treatments. The concentration of inorganic nitrogen was significantly higher in the CF treatment, whereas organic nitrogen was higher in treatments NN, DA, and NA. This suggests that primary production is higher in static ponds. Thermal stratification started at 0900 h, and the maximum difference between surface and bottom temperature varied from 1.5 (CF) to 2.8 C (NN). The difference between DO levels in the surface and bottom water of the ponds began to appear at 0800 h and varied from 0.50 (CF) to 5.23 mg/L (NN). Diurnal aeration and high continuous water flow were efficient in disrupting the stratification. No significant difference was found for survival, mean weight, apparent feed conversion rate, and productivity among treatments. Thus, disrupting water stratification, aerating ponds at night, or exchanging the pond water are ineffective in Amazon River prawn farming in semi‐intensive systems, at least for stocking densities lower than 40 individuals/m². About 1000 kg of Amazon River prawn can be produced in static ponds with no aeration in approximately 4 mo. This management strategy saves water and energy and reduces production costs .     

增氧与投饵对海蜇足囊萌发的影响

对久置海蜇(Rhopilema esculentum Kishinouye)螅状体足囊在不同培养条件下的萌发状况进行了为期1个星期的连续观察.结果表明,海蜇进行横裂生殖苗种生产后的附着基,弃置3个月后其上的足囊仍然具有萌发能力.这些足囊在投饵并充气增氧、仅充气增氧不投饵、仅投饵不充气增氧3种情况下的萌发率分别为69.08%、48.83%、34.90%,充气增氧情况下的足囊萌发率显著高于不充气增氧的情况(P<0.01),投饵情况下的足囊萌发率高于不投饵的情况.结果说明,足囊作为海蜇度过不良环境条件的一种有效策略,其萌发与否在海蜇足囊繁殖过程中更为重要.在溶解氧含量并不成为限制因素的情况下,充气增氧所带来的涡旋水流刺激是促进海蜇足囊萌发更主要的因素,可能和所投喂饵料的体外分泌物一样成为食物丰歉程度的一种信号,进而促进或诱发海蜇足囊的萌发.本研究旨在探讨提高海蜇足囊前发率的有效手段,为提高海蜇苗种培育效率提供基础依据.     

Parental care in response to natural variation in nest predation pressure in six sunfish (Centrarchidae: Teleostei) species

Abstract – Parental care is an important, energetically costly component of the life history of many fishes. Despite this importance, little is known about how different species of fish vary parental care in response to natural nest predator burdens. In this study, underwater videography was used to quantify parental care activity of six species of syntopic nesting male centrarchid fishes in Lake Opinicon, Ontario, in response to natural predators. This approach was used to test the hypothesis that as offspring develop from eggs to wrigglers, parental care activity should decrease or remain static for fish guarding nests with low predator burden and increase for those with high predator burden, reflecting different external risks. Principal components analysis (PCA) was used to derive common aeration and nest defence variables. Aeration and predator defence activity of the fish varied extensively among species. Parental care behaviours indicative of defence and vigilance (e.g., turning, departures, time away from nest, displays) tended to be highest for species that had the most predation attempts, although this was not entirely consistent. There was also a positive relationship between the defence PCA metric and attempted predation. Defence did not vary with stage of offspring development, although interactions between defence and developmental stage were noted for several species. A trade‐off between aeration and defence was not observed. In fact, species that provide high levels of aeration also simultaneously provide high levels of defence. Stage‐specific patterns of defence in this study were less apparent than those documented by studies using responses to staged predator intrusions making it unclear as to the extent that fish were responding to the level of the risk to offspring than to the value of the brood. Therefore, combined use of observational and experimental assessments of parental care investment may be most appropriate for refining current theoretical paradigms.     

Degradation of Trifluralin in Seawater When Used to Control Larval Mycosis in Penaeid Shrimp Culture

Treflan (trifluralin, Elanco) is among the compounds used in the treatment of larval mycosis in penaeid shrimp caused by the phycomycetous fungi hagenidium sp. and Sirolpidium sp. Some culturists have reported treatments for these fungi with trifluralin to be ineffective while others have found it to be quite efficacious.
To study losses of trifluralin in seawater systems, experiments were conducted under varying conditions of aeration, lighting, and algal biomass using nominal concentrations of 19.3 to 65.5 ppb trifluralin. There was no detectable loss of trifluralin over a six hour period in seawater mechanically stirred and covered to prevent photodegradation. Under varying conditions of aeration and light, the estimated half-life of trifluralin ranged from 30 to 138 min. When diatoms were added to the seawater, trifluralin levels dropped to 4% of theoretical within two to three min. These observations confirm the need for a continuous administration for trifluralin to be effective in treating larval mycoses in penaeid shrimp hatching facilities.     

Response of biota to aeration rate in low water exchange ponds farming white shrimp, Penaeus vannamei Boone

The response of phytoplankton, zooplankton and benthos to four aeration rates was evaluated in ponds farming white shrimp, Penaeus vannamei Boone, with less than 5% water exchange. Phytoplankton biomass (measured as chlorophyll-fl) was higher in ponds with aeration rates of 0 and 6 h day^?1 than in those with rates of 24 hday^?1. The abundance of zooplankton and benthos (organisms m^?2) were higher in ponds with aeration rates of 0 and 6 h day^?1, and lower in ponds with rates of 12 and 24 h day^?1. The nauplii of different crustaceans, copepods and larval polychaetes were the most abundant organisms of the zooplankton community. Differences in zooplankton composition were observed among treatments. Polychaetes were the most abundant benthic organisms during the culture period. These organisms were more abundant in ponds with lower aeration rates. The guts of shrimp from ponds with aeration rates of 0 and 6 h day^?1 had a higher abundance of zooplankton and benthic organisms than those from the other treatments. That abundance decreased over time in all treatments. Shrimp had better growth in ponds with an aeration of 6 hday^?1. Survival and yield were similar in ponds with aeration rates of 6, 12 and 24 h day^?1, and lower in ponds with rates of 0 h day^?1.     

Economics of Intensively Aerated Catfish Ponds

The US catfish industry is evolving by adopting production‐intensifying practices that enhance productivity. Catfish producers have increased aeration rates over time, and some now use intensive rates of aeration (>9.33 kW/ha). Costs and production performance were monitored at commercial catfish farms using high levels of aeration (11.2–18.7 kW/ha) in Alabama, Arkansas, and Mississippi. A multivariate‐cluster analysis was used to identify four different management clusters of intensively aerated commercial catfish farms based on stocking density, size of fingerlings at stocking, and feed conversion ratios (FCR). Breakeven prices of hybrid catfish raised in intensively aerated pond systems were estimated to range from $1.86/kg to $2.17/kg, with the lowest costs associated with the second greatest level of production intensity. The two medium‐intensity clusters generated sufficiently high revenues for long‐term profitability. However, the least‐intensive and the most‐intensive clusters were economically feasible only when catfish and feed prices were closer to less probable market prices. Feed price, FCR, and yield contributed the most to downside risk. Intensive aeration in catfish ponds, up to the levels analyzed in this study, appears to be economically feasible under the medium‐intensity management strategies identified in this analysis.     

Oxygen recharge and ammonia stripping capabilities of various closed culture configurations

A packed tower (trickling filter), empty, half full and full of a medium (styrofoam packing material) and a rotating biological contactor (RBC, rotating disc) were tested at various recirculating flow rates, with and without supplemental aeration, to determine oxygen recharge and ammonia stripping capabilities. Oxygen recharge capabilities increased with increasing flow rates, but at different rates for each filter. Oxygen recharge efficiencies decreased as flow rates increased in the half full and empty towers, were about constant for the full tower and increased in the RBC. Oxygen recharge capabilities were significantly increased with the addition of surface agitation; greater than the sum of the component contributions. With supplemental aeration, the full tower with a recirculation flow of 45·4 liters/min was most efficient and capable of supplying the most oxygen. Ammonia stripping was found to be insignificant in all systems tested.     

Estimating stock depletion level from patterns of catch history

The degree to which a stock is depleted is one of the most important quantities in fisheries management because it is used to quantify the success of management and to inform management responses. However, stock depletion is extremely difficult to estimate, particularly with limited data. Using the RAM Legacy database, we developed a boosted regression tree (BRT) model to correlate depletion with a range of predictors calculated from catch data, making the model usable for many fisheries worldwide. The most important predictors were found to be catch trends obtained from linear regressions of scaled catch on time, including regression coefficients for the whole catch time series, the subseries before and after the maximum catch, and in recent years. Eight predictors explain about 80% of variation in depletion. There is a correlation of .5 between measured levels of depletion and the predictions of the BRT model. Predictions are less biased when the stock is fished down below half of the carrying capacity. The BRT model outperforms comparable existing catch‐based depletion estimators and could be used to provide priors for depletion for data‐poor stock assessment methods, or used more directly to provide estimates of the probability that depletion is below a given threshold value.     

持续充氧对养殖池塘上覆水—泥水界面—沉积物间隙水中离子垂直分布的影响

为研究底部充氧对养殖系统上覆水—泥水界面—沉积物间隙水中离子垂直分布的影响,在室内条件下构建模拟装置,设充氧组(实验组)和未充氧组(对照组),每组4个平行,利用Peeper技术分别采集各装置中第0、1、4和7天,上覆水—泥水界面—沉积物间隙水整个垂直剖面的原位水样,然后应用微量分光光度法测定样品中的NH_4~+-N、NO_3~-N、NO_2~--N、PO_4~(3-)-P和SO_4~(2-)-S浓度。结果显示:(1)短期充氧对NH_4~+-N在上覆水和沉积物间隙水中的垂直分布特征影响不显著;(2)充氧可使沉积物上覆水和表层沉积物(0~2 cm间隙水中的NO_3~--N浓度大幅升高;(3)硝化作用的中间产物NO_2~--N,由于不能和氧气大量共存,其平均浓度的最大值由未充氧前出现在上层上覆水,逐渐转变为在表层沉积物1 cm深处;(4)充氧促进了沉积物对PO_4~(3-)-P的吸附和固定,显著降低了其在上覆水和表层沉积物(0~2 cm)间隙水中的浓度;(5)充氧通过化学和生物途径氧化了系统中还原性含硫物质,大幅升高了上覆水和表层沉积物(0~2 cm)间隙水中的SO_4~(2-)-S的浓度;(6)主成份分析(PCA)表明,持续充氧1、4和7 d显著改变了上覆水的理化性质,其中第4天和第7天的数据与对照组差异最大,相对于上覆水,充氧对沉积物间隙水的总体影响不显著。研究表明,底部充氧可降低引起池塘富营养化PO_4~(3-)-P的浓度,提高了氧化性离子NO_3~--N、NO_2~--N和SO_4~(2-)-S的浓度,显著改变了上覆水和表层沉积物间隙水的理化性质,是养殖池塘水质调控和环境修复的一种有效方法。     

一种新型管式曝气装置的设计与试验

随着水产养殖业逐渐向高密度、集约化方向的发展,为实现氧气(O_2)高效溶解、二氧化碳(CO_2)调控、流态改善等目的,急需研制新型高效曝气装置,开发高效节能的曝气技术。基于气水两相溶解的双膜理论和文丘里原理,设计开发了一种管式曝气装置,经初步试验获得了影响增氧性能的关键技术参数,并以此为基础对曝气装置进行优化设计,研究新型节能增氧技术。试验结果表明,管式曝气装置中影响曝气效果的因素有水面高程(Hw)、缩径(D_1/D_2)、旋混结构、进气口大小、进气量等。水面高程、缩径、进气口越大,进气量越充足,曝气装置的增氧效果越高;而额外增加延长结构和旋混结构后,曝气装置水头损失增大、进气量下降,从而导致增氧效果显著下降。该装置利用额外水流动力实现增氧,是一种高效、节能、经济的新型曝气装置,可为水产养殖提供一种新的增氧方法。     

Reaction of common carp (Cyprinus carpio, L.) to oxygen deficiency in winter as an example for the suitability of radio telemetry for monitoring the reaction of fish to stress factors in pond aquaculture

The reaction of common carp (Cyprinus carpio L.) in an ice‐ and snow‐covered pond to depletion of dissolved oxygen (DO) in winter was recorded using radio telemetry. The carp moved from the deeper parts of the pond to the shallow areas near the tributary in search of better oxygenated water. Evidence was found that feeding occurred until December but ceased with the oxygen crisis. After the carp farmer started aeration to improve the oxygen supply, carp returned towards the deeper parts of the pond. The gross activity was significantly correlated with DO (P<0.001) and was not influenced by water temperature (P>0.05). The clear documentation of the carp's reaction to oxygen depletion suggests, that radio telemetry may be useful for investigating the effects of various stress factors on fish in pond aquaculture.     

Winter Culture of Yellowleg Shrimp Penaeus californiensis in Aerated Ponds with Low Water Exchange

Abstract— This study was conducted in the semiarid region of Bahia Kino, Sonora, Northwestern Mexico to determine the feasibility of farming yellowleg shrimp Penaeus californiensis during the winter season in ponds with less than 5% daily water exchange and aeration. Four aeration rates (0, 6, 12, and 24 h/d) were used in the study. Mean growth rates ranged from 0.41 to 0.53 g/wk with the highest growth rate in ponds with 12 h of aeration ( P × 0.05). Survival ranged from 50 to 52% and did not differ among treatments. Shrimp yield ranged from 1,012 to 1,208 kg/ha, with the highest yields from ponds with 6 and 12 h of aeration ( P × 0.05). Feed conversion ratios ranged from 2.3 to 2.8, with lower values in ponds with 12 and 6 h of aeration ( P × 0.05). Results suggest that winter culture of yellowleg shrimp is possible and that 6 h of aeration is sufficient to maintain good water quality conditions.