Treatment of flow-through trout aquaculture effluents in a constructed wetland

A study on effluent treatment with sub-surface flow (SF) constructed wetlands was conducted in a small commercial scale Bavarian (Germany) flow-through trout farm. Under limited spatial and financial conditions a most suitable wetland was constructed. The wetland treatment efficiency at high hydraulic loading rates during raceway runoff and cleaning situation in comparison to sedimentation as initial treatment method was examined.

The constructional solution involved the alteration of six existing sedimentation basins (SB) to SF horizontal flow constructed wetlands with a pre-sedimentation area. As constructional materials only local, cheaply available materials were used in order to reduce the costs. The SF wetland had high treatment efficiencies in the two operational modes examined. During cleaning situation at a hydraulic loading rate (HLR) of 13.6 m/day treatment efficiency for total suspended solids (TSS) was highest and reached 68%. While during raceway runoff situation total ammonia nitrogen (TAN) treatment efficiency of 88% overtopped the efficiency of the other nutrients examined at a HLR of 10.6 m/day. In both treatment situations the SF wetland efficiency was significantly higher than the effect of the SB. SF constructed wetlands treating high hydraulic loading rates accompanied with short retention times were effective on dissolved nutrient treatment only for TAN and nitrite nitrogen (NO₂–N), while other dissolved nutrients like nitrate nitrogen (NO₃–N) and phosphate phosphorous (PO₄–P) showed no or even negative treatment effects through the wetland passage. To reduce these nutrients, other treatment conditions or wetland configurations are needed.     

Nitrogen removal techniques in aquaculture for a sustainable production

As the aquaculture industry intensively develops, its environmental impact increases. Discharges from aquaculture deteriorate the receiving environment and the need for fishmeal and fish oil for fish feed production increases. Rotating biological contactors, trickling filters, bead filters and fluidized sand biofilters are conventionally used in intensive aquaculture systems to remove nitrogen from culture water. Besides these conventional water treatment systems, there are other possible modi operandi to recycle aquaculture water and simultaneously produce fish feed. These double-purpose techniques are the periphyton treatment technique, which is applicable to extensive systems, and the proteinaceous bio-flocs technology, which can be used in extensive as well as in intensive systems. In addition to maintenance of good water quality, both techniques provide an inexpensive feed source and a higher efficiency of nutrient conversion of feed. The bio-flocs technology has the advantage over the other techniques that it is relatively inexpensive; this makes it an economically viable approach for sustainable aquaculture.     

Proposal and assessment of an aquaculture recirculation system for trout fed with harvested rainwater

A sustainable aquaculture production involves alternatives, as recirculating aquaculture systems (RAS), in order to increase the water supply efficiency. This paper aims: a) to propose a method for dimensioning a RAS filled and additionally supplied with water from a rainwater harvesting systems (RHS) and; b) to evaluate the efficiency of the system based on the supply of rainwater from the RHS, the quality of water in the RAS, and the development of aquatic organisms. A pilot aquaculture farm for rainbow trout (Oncorhynchus mykiss) production was designed and dimensioned. On one hand, the RAS with a configuration based on a treatment tower provided acceptable values of pH, TAN, and alkalinity. The temperature was slightly above the recommended temperature but did not negatively impact trout development. On the other hand, the water use efficiency reached 178 L/kg of fish, instead of 210,000 L/kg in an open flow system for trout rearing. The RHS fulfilled the additional required water on the test period of the pilot farm and is expected to supply at least 92% on average during the useful life. Regarding the aquatic organisms’ development, the system allowed both a better Length/ weight ratio and a lesser mortality rate compared to previous studies of RAS. In contrast to other studies in the literature, the mathematical models for dimensioning the system were calculated as a function of the final biomass expected in the tank instead of the quantity of supplied feed. Therefore, this method confirmed the applicability of this alternative criterion for designing biofilters and aquaculture systems.     

海水工厂化养殖生产能力评估方法

生产能力反映出海水工厂化养殖企业的可蓄养生物资源量,是评估海水工厂化养殖企业生物资源资产的重要指标,本文根据海水工厂化养殖的特点,提出了评估海水工厂化养殖企业生产能力的技术思路与原则,并在详细论述影响生产能力主要因素的基础上,提出了具体的评估方法,同时阐述了此方法的实用性和对完善海域评估方法的意义。     

Off flavor characterization and origin in French trout farming

The results of a study on off-flavor problems in four French trout (Onchorynchus mykiss) farms are presented. Methodological aspects on sensory analyses and volatile compounds quantification in fish are discussed. Detection of odorous compounds by gas chromatography–mass spectrometry shows that significant concentrations of geosmin (up to 18 μg/kg in fat) are found in trout. The sensory evaluation, the presence/absence of geosmin in the flesh and the identification of off-flavor compounds producers demonstrate the implication of Microcoleus in the appearance of earthy/musty off-flavors. The presence of this particular cyanobacterium is linked to the deterioration of water quality during the water recirculation period. Correlations between chemical and sensory detection in the flesh indicate that the taste evaluation enables the differentiation of the four categories “non-tainted”, “slightly-tainted”, “tainted” and “strongly-tainted”. However, the average concentrations of geosmin found for these different intensities are relatively limited, from 0.2 to 4.9 μg/kg. Finally, recommendations are made to allow a more effective control of off-flavor occurrences.     

大鹏澳网箱养殖海域水质评价及因子分析

根据2001年6月至2002年6月对大鹏澳网箱养殖海域6个航次的水质监测数据,采用有机污染评价指数法对养殖区水质状况进行了评价,同时应用因子分析方法对T(水温)、DO、SS(悬浮物)、CoDMn、BOD5、NO2-N、NO3-N、NH3-N、TIN(总无机氮)、PO4-P等10个水质成分的监测数据进行了分析。结果表明,(1)2001年9月和2002年3月海水出现轻度污染,前者主要是由NO3-N、CoDMn和BoD5所引起,后者是由NH3-N、PO4-P引起的。(2)水质监测数据的总体方差主要来源于T、Do、SS、NO3-N及TIN等5个成分,其次是NO2-N、NH3-N、PO4-P,再次是CODMn和BOD5。(3)因子分析结果表明,各水质成分之间存在一定的相关关系。其中,T、Do、SS、NO3-N及TIN同时载荷于第1主因子上,说明此5个水质成分之间具有较好的相关性;NO2-N、NH3-N、PO4-P同时载荷于第2主因子上,则此3个水质成分之间的相关程性较好;CODMn和BOD5同时载荷于第3主因子上,二者之间具有较好的相关性。     

Validation of two dilution models to predict chloramine-T concentrations in aquaculture facility effluent

Accurate estimates of drug concentrations in hatchery effluent are critical to assess the environmental risk of hatchery drug discharge resulting from disease treatment. This study validated two simple dilution models to estimate chloramine-T environmental introduction concentrations by comparing measured and predicted chloramine-T concentrations using the US Geological Survey’s Upper Midwest Environmental Sciences Center aquaculture facility effluent as an example. The hydraulic characteristics of our treated raceway and effluent and the accuracy of our water flow rate measurements were confirmed with the marker dye rhodamine WT. We also used the rhodamine WT data to develop dilution models that would (1) estimate the chloramine-T concentration at a given time and location in the effluent system and (2) estimate the average chloramine-T concentration at a given location over the entire discharge period. To test our models, we predicted the chloramine-T concentration at two sample points based on effluent flow and the maintenance of chloramine-T at 20 mg/l for 60 min in the same raceway used with rhodamine WT. The effluent sample points selected (sample points A and B) represented 47 and 100% of the total effluent flow, respectively. Sample point B is analogous to the discharge of a hatchery that does not have a detention lagoon, i.e. the sample site was downstream of the last dilution water addition following treatment. We then applied four chloramine-T flow-through treatments at 20 mg/l for 60 min and measured the chloramine-T concentration in water samples collected every 15 min for about 180 min from the treated raceway and sample points A and B during and after application. The predicted chloramine-T concentration at each sampling interval was similar to the measured chloramine-T concentration at sample points A and B and was generally bounded by the measured 90% confidence intervals. The predicted average chloramine-T concentrations at sample points A or B (2.8 and 1.3 mg/l, respectively) were not significantly different (P>0.05) from the average measured chloramine-T concentrations (2.7 and 1.3 mg/l, respectively). The close agreement between our predicted and measured chloramine-T concentrations indicate either of the dilution models could be used to adequately predict the chloramine-T environmental introduction concentration in Upper Midwest Environmental Sciences Center effluent.     

The impact of production intensity on water quality in oxygen enriched,floating enclosures for post-smolt salmon culture

The main aim of the study was to decide the effect of specific water consumption (L/kg/min) and feed load per water flow (g/m³) on the water quality parameters pH, CO₂, total ammonia nitrogen (TAN) and suspended solids (SS) in two large semi-closed containment systems (S-CCS). The reported production parameters (range) in the two S-CCS were specific water consumption (q): 0.04–0.47 L/kg/min and feed load per water flow: 9.0–64 g/m³. The study period was split in two sub-periods; January–May (4.4–7.5 °C), and June–September (7.5–13.2 °C) before a regression model was used to determine the relationship between production intensity (q, feed load) and water quality (pH, CO₂). With the acceptable level of CO₂ defined as ≤10 mg/L, the model predicted a minimum specific water consumption (L/kg/min) between 0.07 (winter) and 0.2 (summer). The predicted maximum feed load per water flow (g/m³) was between 35 (summer) and 45 g/m³ (winter). These calculated limits for production intensity were close to the values earlier reported for smolt or post-smolt production in large, onshore tanks.     

Foam fractionation and ozonation in freshwater recirculation aquaculture systems

Foam fractionation is often considered an ineffective way of removing organic matter from freshwater due to the low surface tension of the water. There is, however, a lack of studies testing foam fractionation efficiency in replicated freshwater recirculating aquaculture systems (RAS). Foam fractionation can be applied with or without ozone. Ozone is a strong oxidiser previously shown to improve water quality and protein skimmer efficiency. To test the efficiency of foam fractionation and ozonation (20 g O₃ kg^-1 feed) separately and in combination in freshwater RAS, a two-by-two factorial trial was conducted with each main factor at two levels (applied or not applied). Each treatment combination was carried out in triplicates using 12 replicated pilot scale RAS stocked with juvenile rainbow trout (Oncorhynchus mykiss) and operated at a feed loading of 1.66 kg feed m^-3 make-up water. The trial lasted 8 weeks and samples were obtained once a week. Ozone applied by itself significantly reduced the number of particles (83%), bacterial activity (48%) and particulate BOD₅ (5-days biochemical oxygen demand; 54%), and increased ultra violet transmittance (UVT; 43%) compared to the untreated control group. Foam fractionation by itself lead to significant reductions in particle numbers and volume (58% and 62%, respectively), turbidity (62%), bacterial activity (54%) and total BOD₅ (51%). A combination of both treatments resulted in a significant additional improvement of important water quality variables, including a 75% reduction in total BOD₅, 79% reduction in turbidity, 89% reduction in particle numbers and 90% reduction in bacterial activity compared to the control. The removal efficiencies were within the same range as those observed in previous studies conducted with foam fractionators in saltwater systems (with or without ozone), corroborating that foam fractionation may become a useful tool for controlling organic matter build-up and bacterial loads in freshwater RAS.     

Review of climate change impacts on marine aquaculture in the UK and Ireland

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Nutrient discharge,sludge quantity and characteristics in biofloc shrimp culture using two methods of carbohydrate fertilization

The aim of this study was to evaluate the effect of two methodologies of carbohydrate fertilization on the volume and characteristics of effluent from intensive biofloc shrimp cultivation. Six fiberglass circular tanks (50 m² each) were divided into two treatments. In the treatment called continuous (CONT), the tanks received daily molasses fertilization throughout the entire rearing period. In the treatment named initial (INI), molasses was used only in the early weeks of cultivation. Juvenile Litopenaeus vannamei (0.87 ± 0.10 g) were stocked at a density of 180 animals m⁻² and cultured during 12 weeks until they reached an average weight of 12 g. The tanks were operated with no water exchange and the total suspended solids concentration were kept between 300 and 400 mg L⁻¹ using settling chambers. The sludge produced and the wastewater at harvest were quantified and their characteristics were determined. The production of TSS in the CONT treatment was higher (0.25 kg of solids per kg of applied feed) than in the INI treatment (0.16 kg kg⁻¹) (P < 0.05). The analysis of the sludge revealed a high amount of volatile solids in both treatments, between 636 and 702 g kg⁻¹. However, due to the elevated sludge nitrogen content, the carbon to nitrogen (C:N) ratio was low, with values of 6.4 ± 1.4 and 7.5 ± 1.6 for INI and CONT respectively. The BOD:TSS ratio was also low in both treatments, but the INI showed lower values (10.3 ± 0.6%) than the CONT (14.9 ± 0.0%) (P < 0.05). Both fertilization strategies were able to modify the characteristics of sludge produced during cultivation. Moreover, the high nitrogen and sulfate content of the sludge in both treatments indicated that it may be difficult to use an anaerobic digestion process to treat sludge. In the INI treatment tanks, the sludge is partially stabilized, while in the CONT there was a greater need for stabilization.     

生物絮团在斑节对虾养殖系统中的形成条件及作用效果

试验以生物絮团技术 (Biofloc technology, BFT) 养殖30 d的凡纳滨对虾 (Litopenaeus vannamei) 及其池塘水体为基础,设定红糖持续添加组 (BS-组) 和不添加红糖组 (NBS-组),探究在稳定的凡纳滨对虾生物絮团 (Bioflic, BF) 养殖系统中,适时停止添加红糖对养殖水质和氮收支的影响。在28 d内监测总氨氮 (TAN)、亚硝酸盐氮 (NO₂ ^– -N) 等,并测定试验前后虾体和投喂饲料的总氮 (TN)。结果显示,BS组和NBS组的TAN、NO₂ ^– -N均处于较低水平,试验期间两组TAN质量浓度维持在0.02~0.06 mg·L⁻¹,试验第7天后两组NO₂ ⁻-N质量浓度在1.00 mg·L⁻¹以下。研究发现：1) 氮收入主要为饲料,占比78.8%;氮输出主要为水体TN,BS组和NBS组的水体TN分别占45.06%和52.55%;2) 收获虾体的氮输出分别占21.49%和25.43%,两组的饲料氮利用效率分别为18.14%和23.14%。可见,在稳定的BF养殖系统中适时停止添加红糖,对水体微生物去除TAN和NO₂ ^– -N的效果不会产生影响。

     

宁夏地区不同模式养殖池塘夏季浮游微藻群落特征

为研究宁夏地区夏季不同模式养殖池塘的浮游微藻群落结构特征,采集了当地棚塘接力养殖(PT)、稻渔种养(DY)、土池养殖(TC) 3种模式的池塘水体样品,分析了其浮游微藻群落组成及其与水质因子的相关性。结果显示,共检出浮游微藻5门27属,总数量为1.52×104~2.39×108 ind./L,生物量为0.16~97.78 mg/L,数量多样性为0.03~3.31,生物量多样性为0.29~3.58。不同模式池塘的浮游微藻群落结构差异显著。PT模式池塘的微藻群落无明显共性特征,蓝藻(Cyanophyta)、绿藻(Chlorophyta)和硅藻(Bacillariophyta)占优势情况均有出现,如拟鱼腥藻(Anabaenopsis sp.)、鱼腥藻(Anabaena sp.)、颤藻(Oscillatoria sp.)、盘星藻(Pediastrum sp.)、卵囊藻(Oocystis sp.)、小环藻(Cyclotella sp.)等;TC模式池塘的微藻优势属单一,分别以盘星藻、小球藻(Chlorella sp.)和微囊藻(Microcystis sp.)占优势;DY模式池塘的微藻多样性丰富,以小球藻、栅藻(Scenedesmus sp.)、盘星藻、卵囊藻、刚毛藻(Cladophora sp.)等绿藻和小环藻、菱形藻(Nitzschia sp.)等硅藻为优势藻。蓝藻生物量与水体中硝酸盐氮(NO3–-N)、亚硝酸盐氮(NO2–-N)、化学需氧量(COD)浓度呈显著正相关(P<0.05)。研究表明,宁夏地区夏季温度高、光照时间长,池塘水体中C、N营养高,易形成以微囊藻、拟鱼腥藻等有害蓝藻优势种群;调控池塘水质时应将其作为关键控制点之一,防控有害藻华暴发而导致减产降效的不良状况发生。     

An integrated recirculating aquaculture system (RAS) for land-based fish farming: The effects on water quality and fish production

To mitigate the serious water pollution caused by the rapid expansion of the aquaculture industry in recent years, the development of improved aquaculture systems with more efficient water usage and less environmental impact has become essential. In this study, a land-based recirculating aquaculture system (RAS) was established that consisted of purification units (i.e., a primary biological pond, two parallel horizontal subsurface flow constructed wetlands [CWs], and a long ecological ditch) and 4-5 series-connected recirculating ponds. This system was mainly designed to stock channel catfish (Ictalurus punctatus), fifteen spine stickleback (Spinibarbus sinensis) and yellow catfish (Pelteobagrus fulvidraco), and the culture efficacy was evaluated based on a 2-year field experiment covering two growing seasons. According to the results, the primary biological pond played a role in sedimentation or nutrient retention, although this was not as evident when the CWs were functioning. The water flowing through the wetland system at a hydraulic loading rate (HLR) of 600 mm/day displayed lower values for the temperature, pH, dissolved oxygen (DO), suspended solids, organic matter and nutrients, whereas the electrical conductivity (EC) was higher, suggesting the accumulation of dissolved solids in the system. Due to the recirculation treatment, the trophic status of the recirculating ponds increased gradually along the direction of the flow and was notably lower in comparison to the control. As a result, the fish production responded to the variation of the water quality, which was reflected in the measurements of culture efficacy (final weight, survival rate, SGR and yield). The three main rearing species showed a decreasing trend along the direction of the flow, which was higher compared to the control, whereas an opposite trend was observed for filter-feeding fish. A Pearson correlation analysis revealed that the main culture species were inclined to live in meso- or oligotrophic conditions, and the silver carp adapted to more eutrophic conditions. Because RAS can provide better environmental conditions year-round, the present culture method could be more suitable for species that are sensitive to water quality in typical subtropical areas.     

生物絮团在凡纳滨对虾封闭养殖试验中的形成条件及作用效果

为探讨生物絮团技术应用于龟鳖类养殖中的可行性,并确定其最佳添加量,通过调控中华草龟 (Chinemys reevesii) 养殖水体中的碳氮比（质量比）,分析生物絮团形成及其对水质和菌落的影响。实验以添加蔗糖设计碳氮比为10∶1 (CN-10)、15∶1 (CN-15)、20∶1 (CN-20) 的实验组和对照组 (CG),进行为期40 d的养殖。结果显示,各组生物絮团体积指数 (FVI) 随碳氮比的增加而增大,在28 d后趋于稳定;碳氮比≥10时氨氮和亚硝酸盐处理效果显著,其中CN-15组40 d后氨氮和亚硝酸盐的去除率分别为76.7%和64.4%。碳氮比为15∶1时能促进龟池生物絮团的形成,并可有效降低水中氨氮、亚硝酸盐水平。对实验组 (CN-15) 与对照组的生物絮团进行高通量测序,发现2种水体中生物絮团的优势菌门均为变形菌门、拟杆菌门、放线菌门,但各优势菌门占比有所差异。研究表明,添加不同碳氮比可影响中华草龟养殖水体生物絮团的形成、水质和菌群结构。碳氮比为15∶1是形成生物絮团的最适比例,在促进生物絮团形成的同时,对水质也具有较强的调节能力。     

国外发展中国家水产养殖中的环境问题

对调查所获的亚洲、非洲和南美洲的20个国外发展中国家最常见的水产养殖状况、所产生的不利影响和急需的对策支持等数据进行了分析。结果显示,目前的养殖品种至少有90种,表现出较高的多样性。亚洲的水产养殖活动最为明显。除泰国外,所有国家的食粮型养殖品种均高于商业型养殖品种。水产养殖带来的对环境最主要的不利影响为废水污染、环境破坏、药物残留和亲苗掠夺;逃逸灾害、疾病扩散、饵鱼滥捕和生物误捕次之。为消除这些不利影响,这些发展中国家迫切需要在技术更新、科学研究、教育培训和政策扶持等对策方面得到有效的支持。     

Potential and limitations of ozone for the removal of ammonia, nitrite, and yellow substances in marine recirculating aquaculture systems

The high levels of water-reuse in intensive recirculating aquaculture systems (RAS) require an effective water treatment in order to maintain good water quality. In order to reveal the potential and limitations of ozonation for water quality improvement in marine RAS, we tested ozone's ability to remove nitrite, ammonia, yellow substances and total bacterial biomass in seawater, considering aspects such as efficiency, pH-dependency as well as the formation of toxic ozone-produced oxidants (OPO). Our results demonstrate that ozone can be efficiently utilized to simultaneously remove nitrite and yellow substances from process water in RAS without risking the formation of toxic OPO concentrations. Contemporaneously, an effective reduction of bacterial biomass was achieved by ozonation in combination with foam fractionation. In contrast, ammonia is not oxidized by ozone so long as nitrite and yellow substances are present in the water, as the dominant reaction of the ozone-based ammonia-oxidation in seawater requires the previous formation of OPO as intermediates. The oxidation of ammonia in seawater by ozone is basically a bromide-catalyzed reaction with nitrogen gas as end product, enabling an almost complete removal of ammonia-nitrogen from the aquaculture system. Results further show that pH has no effect on the ozone-based ammonia oxidation in seawater. Unlike in freshwater, an effective removal of ammonia even at pH-values as low as 6.5 has been shown to be feasible in seawater. However, as the predominant reaction pathway involves an initial accumulation of OPO to toxic amounts, we consider the ozone-based removal of ammonia in marine RAS as risky for animal health and economically unviable.     

Enhancing water use efficiency in monoculture of Litopenaeus vannamei: Impacts on pond water quality,waste production,water footprint and production performance

We studied the effect of rearing densities of Pacific white shrimp, Litopenaeus vannamei in three densities with three replicate treatments [T₁: 0.4 million post-larvae (PL) ha⁻¹, T₂: 0.5 million PL ha⁻¹, T₃: 0.6 million PL ha⁻¹] and water cutback approach on rearing environment, water use efficiency, water footprint and production performance. Conditional water exchange was carried out based on water quality parameters. Water quality suitability index was very good (7.5–9.0) up to 13th, 10th and 5th week of culture in T₁, T₂ and T₃, respectively; which was attributed to rearing density, smaller-sized shrimp and low early feed input. Optimum rearing density of 50 PL m^-2 (T₂) led to total water use of 3.25 × 10⁴ m³. It was seeming as a way to improve shrimp productivity (10.58 t ha⁻¹ 120 d⁻¹), consumptive water use index (1.72 m³ kg^-1 biomass), total water footprint (1229 m³ t⁻¹ biomass) and net consumptive water productivity (USD 1.28 m^-3). L. vannamei culture with low to moderate water exchange as in T₂, helped uphold water quality suitable for the shrimp growth, improved water use efficiency (0.58 kg biomass m^-3 water), minimized sediment load (45.3 m³ t^-1 biomass), effluent outputs (0.63 × 10⁴ m³), pumping cost (USD 30.1 t⁻¹ biomass produced), and ratio of output value to the cost of cultivation (1.97). The findings and advancement in knowledge would offer the basis to augment shrimp rearing efforts and the water management approaches will help in preventing the production of waste and effluent while increasing water use efficiency and production performance.     

Design and performance of recirculating aquaculture system for marine finfish broodstock development

Tropical and subtropical climatic conditions in India present an ideal and unique opportunity for being the leader in tropical marine finfish aquaculture. However, the problem persist due to non-availability of marine finfish seed for the culture. In response to this problem, broodstock development of different tropical marine finfishes for seed production was started. The present study was undertaken to design a recirculating aquaculture system (RAS) and studying their performance in managing the various water quality required for the marine finfish broodstock development and breeding. The design of RAS, developed in the present study, included a broodstock tank, egg collection chamber, electrical pump, rapid sand filter, venturi type protein skimmer and biological filter. Two RAS were designed, one was stocked with a demersal fish species, orange spotted grouper (Epinephelus coioides) and the other was stocked with a pelagic fish species, Indian pompano (Trachinotus mookalee) at the rate 1 and 0.5 kg/m³ with a sex ratio of 1:1 and 1:2 (female: male) respectively. Various physio-chemical parameters, viz, total ammonia nitrogen (TAN), nitrite, nitrate, pH, alkalinity, temperature, free carbon dioxide (CO₂) and dissolved oxygen (DO) of both tank water were analyzed to assess the performance of recirculating aquaculture system in maintaining the water quality. Gonadal development of the fishes was assessed and the spawning performance was recorded and finally, economic performance of the system was also evaluated. During the entire experimental period, mean monthly total ammonia nitrogen was less than 0.07 and 0.06 mg L⁻¹ and mean monthly nitrite was less than 0.02 and 0.01 mg L⁻¹ in orange spotted grouper and Indian pompano RAS tanks respectively. The pH (7.8–8.2), DO (>4 mg/L) and alkalinity (100–120 mg/L) were found to be in optimum range in both recirculating aquaculture systems. Carbon dioxide was found to be nil during the entire experimental period in both the systems. In fact these levels were comparable or less than that is reported as the permissible limits for broodstock development. Indian pompano and Orange spotted grouper matured and spawning was obtained with production of fertilized eggs round the year. Economic evaluation showed the price of 10,000 fertilized eggs of orange spotted grouper to be US $ 1.33. The design of RAS devised in the present study is efficient in controlling and maintaining optimum water quality for broodstock development of both demersal and pelagic finfishes. The fishes stocked in RAS attained final maturation and round the year spawning was obtained.     

Water quality upstream and downstream of a commercial oyster aquaculture facility in Chesapeake Bay,USA

Oyster aquaculture is an expanding industry in the Chesapeake Bay. Oysters remove nitrogen (N) and phosphorus (P) from the water column through filtration and conversion of phytoplankton into shell and tissue, but also continuously excrete these same nutrients back into the water column as inorganic compounds readily available for plant or algal uptake. The objective of this study was to assess multiple water quality parameters upstream and downstream of a commercial oyster aquaculture facility in the mesohaline region of the Chesapeake Bay. Results of the study indicated a 78.4% average increase in total ammonia nitrogen (TAN) concentration and a 19.4% decrease in chlorophyll-a (Chl-a) concentration downstream of the facility. There was no significant change in the concentration of reactive phosphate (RP), nitrate–nitrogen (NO₃⁻–N), or nitrite–nitrogen (NO₂⁻–N) as water passed through the facility. It was determined that velocity of water through the facility had no influence on the change in TAN or Chl-a concentration from upstream to downstream of the facility. Increased reduction in Chl-a concentration from upstream to downstream was related to higher upstream concentrations of Chl-a. There was no correlation between increased rates of Chl-a removal and downstream TAN. Results of this study suggest that oyster aquaculture can significantly increase the amount of available inorganic nitrogen in the water column immediately downstream of a facility, independent of upstream availability of phytoplankton and flow velocity of water through the facility.