Organic flocculants for the removal of phytoplankton biomass

The formation of noxious phytoplankton blooms causes deterioration of water quality in aquaculture ponds and reservoirs, but also in swimming pools and aquaria. We have studied the effects of selected cationic polyacrylamides on natural phytoplankton community, which was investigated by a decrease of chlorophyll a content in the water column and photosynthetic activity of phytoplankton floccules. Results indicate that cationic polyacrylamides are able to remove more than 80% of phytoplankton biomass. Moreover, no cell damage or lysis was observed by microscopic observation after flocculation. To our knowledge, this is the first report suggesting the removal of cyanobacterial blooms by organic flocculants. Cationic polyacrylamides are biodegradable organic flocculants with low toxicity to aquatic organisms, and seem to be a prospective tool with a possibility for algal or cyanobacterial bloom management in aquaculture.     

Phytoplankton succession in intensive marine shrimp culture ponds treated with a commercial bacterial product

Succession of phytoplankton dominance was studied in shrimp culture ponds treated with commercial bacterial products. Diatoms were dominant and the cyanobacteria were absent in both treated and control ponds at the beginning of the culture period. After 34 days, the diatoms significantly decreased whereas cyanobacteria increased in both ponds. Chlorophyll a increased from a mean of 35.56 mg m^?3 in the first phase to 186.00 mg m^?3 in the final phase, and from 42.12 mg m^?3 to 242.81 mg m^?3 in the treated and control ponds respectively. Cyanobacteria were significantly higher in the control compared with the treated ponds during the final phase of the culture. Algal bioassay showed that the addition of nitrogen either alone or with silica to pond water significantly increased the specific growth rate of Chaetoceros calcitrans. The specific growth rate of Oscillatoria sp. significantly increased when a combination of nitrogen, phosphorus and carbon was added to the pond water. Addition of silica seemed to depress the growth rate of Oscillatoria sp. Nutrient enrichment should be minimized and the supply of nitrogen and silica should be adequate for promoting the growth of beneficial phytoplankton in aquaculture systems.     

春季不同营养类型池塘浮游植物群落结构特征的研究

为了积累池塘浮游植物群落结构的数据,以利于有效调控池塘藻相,2013年春季研究了3口不同富营养池塘的浮游植物和氮、磷营养盐：室外池I、室外池II以及大棚池。结果表明,根据氮、磷营养盐水平,室外池I和大棚池均属超富营养水体,而室外池II属于富营养水体。室外池I的浮游植物种类最多,优势种类是绿藻门和硅藻门,蓝藻门种类和数量均很少,比较适合养殖。而室外池II只有蓝藻门,且种类非常少,仅2种,以蓝藻门隐球藻属（Aphanocapsa）占绝对优势,已经明显形成了隐球藻属水华。大棚池藻类种类比室外池II多,但是也以蓝藻门的隐球藻属为优势。室外池II和大棚池的浮游植物多样性评价等级均为I级,多样性差,而室外池I为II级,多样性一般。本研究表明,春季不同富营养程度的池塘出现不同的浮游植物群落结构,富营养池塘在低温的春季可以形成蓝藻门优势;建立氮磷营养水平与池塘藻相之间的可靠关系需要更多的数据资料支撑。     

富藻养殖水体中金鱼藻和篦齿眼子菜的抑藻效果研究

夏季高温时,养殖水体水华现象频繁发生,给养殖业带来巨大的损失。常见水生植物释放的活性物质在低浓度下可以起到抑藻作用,对藻类调控具有重要意义。本研究采用实验室静态模拟方法,取养殖池塘暴发蓝藻水华的水体,与沉水植物金鱼藻(Ceratophyllum demersum)及篦齿眼子菜(Potamogeton pectinatus)进行共培养,研究这2种沉水植物对养殖水华水体营养水平、藻类生长、藻类结构及浮游藻类生物多样性的影响。结果显示,金鱼藻和篦齿眼子菜可显著降低水华水体氮、磷等营养水平(P<0.05);金鱼藻和篦齿眼子菜可有效抑制水华蓝藻(Cyanobacteria)生长,尤其对颤藻和微囊藻(Microcystis sp.)效果显著(P<0.05),且篦齿眼子菜对水华蓝藻抑制效果更为显著。实验结束时,篦齿眼子菜培养组藻密度下降93.6%,生物量下降98.9%,叶绿素a含量下降60.5%;金鱼藻培养组藻密度下降72.5%,生物量下降86.8%,叶绿素a含量下降54.3%;金鱼藻和篦齿眼子菜的存在可促进养殖水体浮游藻类生物多样性增加,且金鱼藻提高浮游藻类生物多样性效果更显著。金鱼藻培养组浮游藻类生物多样性升高98.4%,篦齿眼子菜培养组浮游藻类生物多样性升高50.3%。本研究结果可为未来生态养殖提供理论依据和参考。     

Phytoplankton Community Structure, Biomass, and Off-flavor: Pond Size Relationships in Louisiana Catfish Ponds

Abstract.— Many aquaculture studies are conducted in relatively small research ponds and the results are then extrapolated to larger commercial ponds. Implicit in this research is the assumption that there is no relationship between pond size and phytoplankton composition. Study objectives were to assess phytoplankton composition and biomass by several methods in 17 channel catfish Ictalurus punctatus ponds at the Aqua‐culture Research Station, Louisiana Agricultural Experiment Station in Baton Rouge, Louisiana, USA. Pond size ranged from 0.04–0.60 ha. Sampling occurred weekly from 10 September – 1 October 1997. Water temperatures coincided with a transition from summer to fall‐winter conditions. Biomass was assessed by cell counts and quantification of photopigments. Concentrations of dissolved off‐flavor compounds (2‐methylisoborneol and geosmin) were assessed by gas chromatography/mass spectroscopy of water column samples. Cell count data showed differences in dominant species, biovolume, and diagnostic pigment signatures among ponds. The smaller ponds had more diverse phytoplankton composition compared to the larger ponds, whereas chlorophyll levels were nearly an order of magnitude lower in the smaller ponds. Ultraplanktonic (2–20 μm) unicellular cyanobacteria dominated the numerical counts on most sampling dates; however, biovolume transformations of cell count data reduced the dominance of this component relative to cryptophytes, diatoms, and filamentous cyanobacteria. Pigment and microscopic analyses were well correlated. Unialgal isolates of dominant taxa from these samples indicated the presence of at least five genera of off‐flavor producers in these ponds; these taxa included Anabaena, Aphanizomenon, Pseudanabaena, as well as two species of Oscillatoria. Care in extrapolating results from smaller‐sized research ponds to larger commercial ponds is warranted, as is the potential for taxa other than Oscillatoria and Anabaena in forming off‐flavor compounds.     

Channel Catfish Polyculture with Fathead Minnows or Threadfin Shad: Effects on Pond Plankton Communities and Catfish Fillet Flavor,Color, and Fatty Acid Composition

Threadfin shad, Dorosoma petenense, or fathead minnows, Pimephales promelas, were co‐cultured with channel catfish, Ictalurus punctatus, in earthen ponds to determine the effects of planktivory on plankton community dynamics and catfish fillet quality. Fathead minnows had no effect on the plankton community structure or catfish fillet flavor, color, and fatty acid composition. Fillet color was also unaffected by the presence of threadfin shad. Small differences were found in fillet fatty acid composition for catfish from ponds with shad, but these differences probably have no biological significance. Threadfin shad did, however, have important impacts on the plankton community structure and catfish flavor. Size‐selective filter‐feeding by shad reduced cyanobacterial abundance relative to ponds with catfish‐only and fathead minnows. Relative abundance of smaller phytoplankton in the groups Chlorophyta, Cryptophyta, Bacillariophyceae, and Euglenophyta increased in ponds with shad. Relative abundance of small zooplankton (rotifers) also increased in shad ponds. Reduced abundance of large, colonial cyanobacteria that are known to produce odorous metabolites caused a corresponding reduction in off‐flavor prevalence and intensity in catfish from ponds with threadfin shad when sampled in September. Although threadfin shad dramatically reduced catfish off‐flavor prevalence during the warm season, they apparently caused a high prevalence of “fishy” off‐flavors in the February sample. This undesirable flavor appeared to be caused by catfish foraging on shad killed during a preceding period of exceptionally cold water temperatures. Use of threadfin shad for phytoplankton biomanipulation therefore presents a dilemma: catfish–shad polyculture reduces prevalence of cyanobacteria‐related off‐flavors in warm months but may cause undesirable forage‐related off‐flavors in the colder months. Catfish farmers must consider these benefits and risks when deciding to use threadfin shad as a management tool.     

东莞市25座水库的营养现状与水质管理对策

为了解东莞市水库富营养化现状并为水质管理提出合理建议,于2011-2012年的丰水期、平水期和枯水期,对东莞市25座水库的营养状态和浮游植物主要参数进行分析。结果显示,中营养水库5座,富营养水库16座,超富营养水库4座,整体富营养化水平较高。水库浮游植物丰度1.07×105~7.67×108个/L,且枯水期高于丰水期;有20座水库的浮游植物丰度中蓝藻比例超过50%,部分水库出现了蓝藻水华现象,其营养状态与人类活动强度、流域内土地利用类型、水库功能及补水方式密切相关。削减外源污染,尤其是控制磷排放是当前遏制水库富营养化的根本途径;对于即将联网调水的5座水库而言,利用联网形成的调度能力进行合理的水库调度是缓解其富营养化的可行措施。     

Low-density silver carp Hypophthalmichthys molitrix (Valenciennes) polyculture does not prevent cyanobacterial off-flavours in channel catfish Ictalurus punctatus (Rafinesque)

Silver carp Hypophthalmichthys molitrix (Valenciennes) were co‐cultured with channel catfish Ictalurus punctatus (Rafinesque) in 0.4 ha earthen ponds to determine the impacts of carp grazing on pond phytoplankton communities and cyanobacterial off‐flavours in catfish. Carp were stocked at densities of 0, 75, or 250 fish ha^?1 in seven replicate ponds per treatment. The mean chlorophyll a concentrations (a measure of phytoplankton standing crop) steadily increased in all treatments from about 100 μg L^?1 in April to more than 400 μg L^?1 by mid‐October. Silver carp had no affect (P>0.1) on chlorophyll a concentrations across all sampling dates (April though October) or for sampling dates late in the growing season (August–October) when the prevalence of cyanobacterial off‐flavours among catfish populations is usually greatest. Silver carp did not eliminate odour‐producing cyanobacteria from pond phytoplankton communities: on sampling dates in September and October, three to six ponds in all treatments contained populations of the odour‐producing cyanobacteria Oscillatoria perornata, Anabaena spp., or both. Failure of silver carp to eliminate odour‐producing cyanobacteria resulted in a relatively high incidence in all treatments of ponds with off‐flavoured catfish. On sampling dates in September and October, catfish in three to five ponds in each treatment were tainted with either musty (2‐methylisoborneol) or earthy (geosmin) off‐flavours. The presence of silver carp had no obvious effect on off‐flavour intensity: on each sampling date, at least three ponds in each treatment contained catfish described as distinctly to extremely off‐flavored. Apparently, hypertrophic conditions in catfish ponds overwhelm the effect of silver carp grazing at the low carp densities used in this study.     

过氧化钙对武汉东湖浮游植物群落及水环境的影响

为探讨过氧化钙作为化学除藻剂对浮游植物群落和水质的影响,于2020年10月采集武汉东湖原水,在深度为2m的水柱中使用不同剂量的过氧化钙进行处理。结果显示：40 mg/L、60 mg/L、80 mg/L的过氧化钙在东湖原水中释放的过氧化氢最高浓度分别为17.04±0.82mg/L、22.21±0.81 mg/L和31.67±2.47mg/L;水柱0~1.0 m水层的过氧化氢含量显著高于1.0-2.0m水层,持续释放时间可达36h~48h;过氧化钙的使用能显著减少底层水体的正磷酸盐含量;同时,过氧化钙在处理12h后可显著降低水柱中叶绿素 a含量和蓝藻的相对丰度（P<0.05）,同时提高了绿藻相对丰度28.06%,将硅藻相对丰度提高了27.25%,改变浮游植物群落的物种优势度,具有选择性杀灭蓝藻的效果。本研究可为过氧化钙在蓝藻水华处置、水体富营养化治理等方面的应用提供参考依据。     

The effects of phosphorus and nitrogen on phytoplankton dominance in tropical fish ponds

Nine ponds were used to determine the effects of phosphorus (P) and nitrogen (N) loading on the phytoplankton dominance in tropical fish ponds. Three ponds received triple superphosphate (TSP), three received triple superphosphate plus urea (TSP-Urea) and the rest served as the control. Addition of both phosphorus and nitrogen (TSP-Urea treatment) resulted in higher total phytoplankton than the TSP treatment and the control (P < 0.05). In general, blue-green algae formed the dominant group in TSP-Urea treatment ponds, followed by dinoflagellates, green algae, euglenoids and diatoms. In TSP-Urea treatment ponds, green algae was the most abundant group followed by blue-green, dinoflagellates, euglenoids and diatoms. Addition of combined nitrogen and phosphorus to the ponds not only significantly increased (P < 0.05) total phytoplankton densities, but also caused a shift from blue-green algal dominance to green algae. TSP treatment ponds showed significantly higher blue-green algae than TSP-Urea treatment in the early culture cycle. However, as the ponds became more productive with time, blue-green algae also appeared to be common in TSP-Urea treatment in spite of high N : P ratios. The blue-green algae increased linearly with the increase of total phytoplankton in all treatments (r²= 0.58, P < 0.01).     

Impact of farming intensity and water management on nitrogen dynamics in intensive pond culture: a mathematical model applied to Thai commercial shrimp farms

A mathematical model is used to investigate the impact of farming intensity and water management on nitrogen dynamics in the water column of intensive aquaculture ponds. The model describes the input of ammonia, its assimilation by phytoplankton or nitrification, and the loss of nitrogen through sedimentation, volatilization, and discharge. The model is calibrated for two commercial shrimp (Penaeus monodon Fabricius) farms in Thailand. Assimilation by phytoplankton with subsequent sedimentation or discharge is the principal process of ammonia removal. When inputs of ammonia exceed the algal assimilation capacity (carrying capacity), nitrification and volatilization of excess ammonia become significant. Carrying capacity is negatively affected by non-chlorophyll turbidity, and was estimated as 6 t ha^?1 cycle^?1 at a non-chlorophyll extinction of 2.6 m^?1. In ponds managed within their carrying capacity, ammonia concentrations are lowest at no water exchange, reach a maximum at exchange rates between 0.2 and 0.4 day^?1, and decline again at higher rates. When the carrying capacity is exceeded, excess ammonia concentrations decline continuously with increasing water exchange. Average exchange rates used in intensive shrimp farms (up to 0.2 day^?1) reduce phytoplankton abundance and sedimentation within ponds, but not ammonia concentrations. Discharges are high in particulate nitrogen at water exchange rates up to 0.3 day^?1, but contain mainly dissolved nitrogen at higher rates.     

主养草鱼与主养黄颡鱼池塘沉积物—水界面氮磷营养盐通量变化及与环境因子的关系

为了探讨不同主养模式池塘养殖期间沉积物—水界面氮磷营养盐通量变化特征以及与环境因子之间的相互关系,利用沉积物—水界面营养盐扩散通量的原位观测装置,分析了2013年4—10月主养草鱼和主养黄颡鱼池塘沉积物—水界面营养盐交换通量,并探讨了影响营养盐交换通量的因素。结果发现:(1)在养殖初期,各种形态氮磷在养殖池塘沉积物—水界面主要表现为从上覆水向沉积物的沉积,养殖中后期,由于温度升高以及池塘沉积物中营养物质的大量累积,各种形态氮磷表现为以沉积物向上覆水扩散为主,表明池塘沉积物是氮磷营养盐的源与汇;(2)两种不同主养模式池塘氮磷通量的统计结果表明,沉积物—水界面-N、-N和-P通量变化无显著差异,而-N、TN和TP通量有显著差异;(3)上覆水中DO含量的升高显著促进界面间-N和-N释放通量,而-N和-P释放通量与上覆水DO浓度成显著负相关;温度的升高对各种无机形态的氮磷通量有显著的促进作用。     

A review of cyanobacterial odorous and bioactive metabolites: Impacts and management alternatives in aquaculture

Increased demand has pushed extensive aquaculture towards intensively operated production systems, commonly resulting in eutrophic conditions and cyanobacterial blooms. This review summarizes those cyanobacterial secondary metabolites that can cause undesirable tastes and odors (odorous metabolites) or are biochemically active (bioactive metabolites) in marine and freshwater, extensive and intensive aquaculture systems. For the scope of this paper, biochemically active metabolites include (1) toxins that can cause mortality in aquaculture organisms or have the potential to harm consumers via accumulation in the product (hepatotoxins, cytotoxins, neurotoxins, dermatoxins, and brine shrimp/molluskal toxins), (2) metabolites that may degrade the nutritional status of aquaculture species (inhibitors of proteases and grazer deterrents) or (3) metabolites that have the potential to negatively affect the general health of aquaculture species or aquaculture laborers (dermatoxins, irritant toxins, hepatotoxins, cytotoxins). Suggestions are made as to future management practices in intensive and extensive aquaculture and the potential exposure pathways to aquaculture species and human consumers are identified.     

Controlling the growth of a cyanobacterial contaminant, Synechoccus sp., in a culture of Tetraselmis chui (PLY429) by varying pH: Implications for outdoor aquaculture production

In aquaculture, large volumes of phytoplankton are often grown outdoors to reduce costs. However, growing microalgae in an environment not as well-controlled as in the laboratory can lead to unwanted phytoplankton, including cyanobacteria, contaminating a culture. A cyanobacterial contaminant was isolated from an outdoor culture of Tetraselmis chui (PLY429) at the Milford Laboratory. This study investigated the growth of PLY429 and the cyanobacterium in pure cultures and a mixed culture in a pH range of 6.5-9.5. The division of PLY429 was greater at a pH range of 7.0-8.0; whereas, for the cyanobacterium, higher growth was obtained at pH 8.0-9.0. Results from combined cultures of PLY429 and the cyanobacterium grown at various pHs indicated that maintaining pH near 7.1 yields higher growth of PLY429 than those of the cyanobacterium. These findings suggest that controlling pH may reduce the population of a cyanobacterial contaminant in an aquaculture feed culture.     

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。     

环境条件变化下滇池冬春季节浮游植物的演替特征

富营养化和气候变暖是影响浮游藻类结构组成以及物候学等特征的两大重要环境条件。为探讨在人为干预和全球变化影响下富营养化湖泊滇池浮游植物的演替特征,2017-2019年2个冬春季在滇池选择北(D1)、中(D2)、南(D3)3个采样点对浮游植物群落进行监测。研究结果表明,滇池浮游植物在冬春季呈现与以往不同的演替特征。第一、滇池在冬春季仍以蓝藻占优势,但优势种组成发生了变化。蓝藻中占主要生物量的是微囊藻,而且,惠氏微囊藻(Microcystis wesenbergii)取代铜绿微囊藻(Microcystis aeruginosa)占绝对优势。近20年来(2001-2019年),滇池冬春季微囊藻优势种经历了从铜绿微囊藻到绿色微囊藻(Microcystis viridis)再到惠氏微囊藻的转变。在水温较低的2-3月份,蓝藻生物量比例下降,绿藻和硅藻生物量比例上升,在此时期,香农威纳指数也相对升高。第二,束丝藻(Aphanizomenon)和鱼腥藻(Anabaena)的物候特征发生了改变。曾经春季的优势水华藻种束丝藻提前在秋季出现,且2018年秋季峰值较2017年约提前2周。2018年春季鱼腥藻在滇池北部发生了小型的水华,取代了往年发生束丝藻水华的现象,2019年春季鱼腥藻没有出现较高的生物量,但仍在春季达到峰值,其峰值约提前1周出现。本研究结果为揭示在全球变化和人为干预影响下湖泊冬春季节浮游植物群落演替特征及响应策略提供了基础数据支撑。     

The timing of inorganic fertilization of sunfish ponds

Fertilization with diammonium phosphate (20 kg/ha per application) was initiated at different dates in each of four treatments replicated three times in 0.04-ha ponds. Although there were some differences in averages of total and filtrable orthophosphate concentrations and phytoplankton abundance among treatments (P < 0.05), sunfish production was not influenced by the timing of fertilization (P > 0.05). Phytoplankton blooms did not develop in any of the treatments until late spring or early summer. The failure of phytoplankton to respond to fertilization in late winter and early spring was apparently related to low water temperature and competition by macrophytes. In larger, deeper ponds (> 0.5 ha), inorganic fertilization will cause phytoplankton blooms in early spring even when water temperatures are low.     

Phytoplankton community structure and diversity in the indoor industrial aquaculture system for Litopenaeus vannamei revealed by high‐throughput sequencing and morphological identification

The explosive multiplication of phytoplankton caused by water eutrophication often occur in the intensive shrimp aquaculture. To comprehensively assess the diversity and community structure of phytoplankton in the waters of typical indoor industrial aquaculture system for Litopenaeus vannamei, a combination of high‐throughput sequencing and morphological identification methods were used in the present study. A total of 41 genera belong to nine phyla were detected by both methods. Chlorophyta, Cyanophyta and Bacillariophyta were found to be three dominant phyla. The high‐throughput sequencing revealed that green algae and cyanobacteria were the most dominant phytoplankton; however, diatoms were the first dominant phytoplankton by using the morphological identification. At the genus level, Picochlorum and Synechococcus were dominant, accounting for 20.94%–97.19% and 0.01%–52.81% of total phytoplankton, revealed by the high‐throughput sequencing. Therefore, more attention should be paid to their ecological impacts on the surrounding sea areas or potential toxicity to shrimp. Cyclotella was the most dominant genus revealed by the morphological identification. High‐throughput sequencing revealed a high diversity and small‐sized phytoplankton which were undetected by microscopy. Both methods provide similar information on the environmental drivers of phytoplankton community. NO₃^?, NH₄⁺, DIP, DSi, DON and DOP concentrations were the main factors influencing the phytoplankton community structure and diversity.     

The use of model ponds to evaluate phytoplankton blooms and benthic algal mats for Penaeus monodon Fabricius culture

Abstract. Fibreglass pools (3·5m diameter, 1·2m high) were evaluated as model ponds and used to compare the effects of fertilization strategies, designed to promote either phytoplankton blooms or benthic algal mats, on production of Penaeus monodon Fabricius and water quality over 8 weeks. As production results were similar to those reported from commercial ponds in Australia and Taiwan, the pools were considered appropriate experimental units for assessing pond management strategies. Large blooms of filamentous algae developed in four of the eight pools with benthic algae. In these, individual prawn growth (weight gain), biomass gain, food conversion efficiency and drain harvest efficiency were all lower ( P < 0·05) than in pools with phytoplankton. Abundance of filamentous algae was negatively correlated ( P < 0·05) with prawn weight gain (r =−0·80) and drain harvest efficiency (r =−0·76). Differences in water quality arising from alternative fertilization strategies occurred but did not explain differences in prawn production indices. The results indicate that ponds used for monoculture of P. monodon should be fertilized so as to stimulate and maintain phytoplankton blooms and to discourage blooms of filamentous algae.     

Photosynthetic suspended-growth systems in aquaculture

Standardized evaluation and rating of biofilters for aquaculture should be assessed in the context of the economic efficiency of ecological services (waste assimilation, nutrient recycling, and internal food production) provided by earthen ponds, and the availability and cost of land, water, and electrical energy resources required to support particular classes of production systems. In photosynthetic suspended-growth systems, water quality control is achieved by a combination of natural and mechanical processes. Natural processes include photosynthesis of oxygen, algal nutrient uptake, coupled nitrification–denitrification, and organic matter oxidation; mechanical processes include aeration and water circulation. Ammonia is controlled by a combination of phytoplankton uptake, nitrification, and immobilization by bacteria. Unlike biofilters for recirculating aquaculture systems, unit processes are combined and are an integral part of the culture unit. The important design and operational considerations for photosynthetic suspended-growth systems include temperature effects, aeration and mixing, quantity and quality of loaded organic matter, and fish water quality tolerance limits. The principle advantages of photosynthetic suspended-growth systems are lower capital costs relative to other recirculating aquaculture systems and increased control over stock management relative to conventional static ponds. The main disadvantage is the relatively low degree of control over water quality and phytoplankton density, metabolism, and community composition relative to other recirculating aquaculture systems. Examples of photosynthetic suspended-growth systems include semi-intensive ponds, intensively aerated outdoor lined ponds, combined intensive–extensive ponds, partitioned aquaculture systems, greenwater tanks, greenwater tanks with solids removal, and greenwater recirculating aquaculture systems.