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.     

Estimation of gut contents of freshwater mussel, Lamellidens marginalis L.

This study examined the food organisms found in the gut of freshwater mussels, Lamellidens marginalis L. A total of 34 taxa of food organisms were recorded, out of which 30 taxa belonged to phytoplankton and four taxa to zooplankton. Both the groups comprised three families each: Cyanophyceae (blue‐green algae), Chlorophycea (green algae) and Bacillariophyceae (diatoms) constituted phytoplankton, whereas Euglenaceae, Chlamydodontidae and Brachionidae belonged to zooplankton. The total number of frequencies of phytoplankton (n=537) were almost nine times more than that of zooplankton (n=60). When blue‐green algae, green algae, diatoms and zooplankton (all the three families together) were tested for significant difference (P<0.05) following Duncan's multiple range test, the result showed only two groups. Blue‐green algae, green algae and zooplankton were not significantly different (P<0.05), forming group A, whereas diatoms were significantly different from others, forming group B. The present study showed that the maximum number of organisms that mussels feed upon belong to green algae, followed by diatoms, blue‐green algae and few taxa of zooplankton.     

Water and Sediment Quality,Phytoplankton Communities,and Channel Catfish Production in Sodium Nitrate-Treated Ponds

Three channel catfish (Ictalurus punctatus) ponds were treated at two-week intervals with sodium nitrate at 2 mg NO₃ ^?-N/L per application and three ponds served as controls. Average concentration of nitrite-nitrogen measured midway between application dates never exceeded 1.2 mg/L in treated ponds, but on most sampling dates, nitrate concentrations were greater than those in control ponds (P < 0.1). Disappearance of nitrate-nitrogen from waters of treated ponds resulted primarily from nitrate reduction to free nitrogen gas. Soluble reactive and total phosphorus concentrations tended to be higher (P < 0.1) in treated ponds than in control ponds. There were no differences (P > 0.1) in pH and concentrations of total alkalinity, total ammonia nitrogen, and dissolved oxygen between treated and control ponds. The higher chlorophyll a concentration (P < 0.1) suggested that greater availability of nutrients in treated ponds resulted in more phytoplankton growth than in control ponds. Because of greater phytoplankton biomass, turbidity was higher and Secchi disk visibility less in treated ponds as compared to control ponds (P < 0.1). There were no obvious differences in phytoplankton community composition with respect to treatment—blue-green algae dominated the phytoplankton community in both treated and control ponds. Redox potential in sediment during crops was higher in ponds treated with sodium nitrate than in control ponds, indicating less anaerobic conditions. However, catfish survival, production, and feed conversion ratio did not differ (P > 0.1) between treatment and control.     

Ecology of Blue-Green Algae in Aquaculture Ponds

Cyanobacteria (blue-green algae) in the genera Anabaena, Aphanizomenon, Microcystis, and Oscillatoria often form extensive and persistent blooms in freshwater aquaculture ponds. Bloom-forming cyanobacteria are undesirable in aquaculture ponds because: 1) they are a relatively poor base for aquatic food chains; 2) they are poor oxygenators of the water and have undesirable growth habits; 3) some species produce odorous metabolites that impart undesirable flavors to the cultured animal; and 4) some species may produce compounds that are toxic to aquatic animals. Development of cyanobacterial blooms is favored under conditions of high nutrient loading rates (particularly if the availability of nitrogen is limited relative to phosphorus), low rates of vertical mixing, and warm water temperatures. Under those conditions, dominance of phytoplankton communities by cyanobacteria is the result of certain unique physiological attributes (in particular, N₂ fixation and buoyancy regulation) that allow cyanobacteria to compete effectively with other phytoplankton. The ability to fix N₂ provides a competitive advantage under severe nitrogen limitation because it allows certain cyanobacterial species to make use of a source of nitrogen unavailable to other phytoplankton. The ability to regulate cell buoyancy through environmentally-controlled collapse ad reformation of intracellular gas vacuoles is perhaps the primary reason for the frequent dominance of aquaculture pond phytoplankton communities by cyanobacteria. Cyanobacteria that can regulate their position in the water column gain a distinct advantage over other phototrophs in poorly mixed bodies of water. In addition to the physicochemical interactions that influence phytoplankton community dynamics, cyanobacterial-microbial associations may play an important regulatory role in determining community structure. Cyanobacteria are always found in close association with a diverse array of microorganisms, including eubacteria, fungi, and protozoans. These associations, which in the past have often been viewed as antagonistic, are increasingly seen as mutualistic and may function in a positive manner during bloom development.     

Diet and food utilization in Oreochromis esculentus (Graham) in Lake Kanyaboli, Kenya

Abstract  Blue-green algae (Cyanophyta) and green algae (Chlorophyta) were the principal food items ingested by Oreochromis esculentus (Graham) in Lake Kanyaboli. Diatoms (Bacillariophyta), euglenoids (Euglenophyta) and zooplankton were also consistently present in the diet in small quantities. O. esculentus of different sizes fed on similar food items in the lake. The species fed actively during the day, from 0700 h until 1700 h when peak feeding activity occurred. Thereafter, digestion took place steadily until 0600 h, when 90% of the fish had empty stomachs. The diet composition remained the same throughout the year, as did the composition of phytoplankton in the lake. O. esculentus tended to select and digest the diatoms and zooplankton and, to some extent, the euglenoids. Blue-green and green algae were the least utilized food items and passed through the gut undigested.     

Effects of Feeding Rate on Habitat Quality in Fish Rearing Ponds

Manufactured feeds are commonly added to earthen ponds to enhance growth and survival of juvenile fish. However, excessive feeding may decrease fish production efficiency and yields by causing hypoxia (dissolved oxygen, DO < 2 mg/L) and stimulating excessive phytoplankton, filamentous green algae, and vascular plant growth. In this study, we quantified the effects of manufactured feed addition (no feeding, 1%, or 3% body‐weight/day, BW/d) on DO and inorganic phosphorus (P) and nitrogen (N) concentrations, plant abundance, and invertebrate prey production in ponds stocked with age‐0 channel catfish, Ictalurus punctatus. We found that the 3% BW/d ponds had lower DO concentrations and greater infestation by filamentous green algae (Rhizoclonium spp.) as compared to the 1% BW/d and no‐feeding ponds. Using stable N and carbon (C) isotopes to trace the fate of feed‐derived N and C in ponds, as well as analysis of zooplankton abundance, we determined that the supplied feed did not support or enhance production of natural invertebrate prey. To improve fish production efficiency, we recommend that managers leverage natural prey support of growth during early life, then adjust feeding levels to enhance growth of older fish and maintain suitable habitat quality.     

Comparison of polyphosphate and orthophosphate as fertilizers for fish ponds

Sodium polyphosphate and triple superphosphate were used as sources of polyphosphate and orthophosphate, respectively, at equal P₂O₅ application rates in sunfish (Lepomis spp.) ponds. Filtrable orthophosphate and total phosphorus concentrations were generally higher in ponds treated with polyphosphate. However, differences between chlorophyll a concentration and net sunfish production did not differ between treatments (P > 0.05).     

养殖池塘青苔(Filamentous algae)发生关键因子调查

以水绵和刚毛藻为代表的青苔广泛存在于各种自然水体和养殖水体,其过度生长对水体环境和养殖动物构成威胁。为探究青苔发生的关键因子,本文通过走访调查,筛选了5组环境相同且隶属同一家养殖户的有青苔池塘和无青苔池塘,重点对水质、底泥生物可利用性氮磷含量及青苔繁殖体进行了检测分析。结果发现,5组有青苔塘、无青苔塘整体水体氮磷水平无显著差异（P > 0.05）,而有4组无青苔塘叶绿素a含量显著高于有青苔塘（P < 0.05）。5组有青苔塘底泥平均生物可利用性氮含量为15.72 ± 3.60 mg/kg,而无青苔塘底泥平均生物可利用性氮为13.22 ± 1.97 mg/kg,较前者低2.50 mg/kg。5组有青苔塘底泥平均生物可利用性磷含量为72.26 ± 10.57 mg/kg,无青苔塘底泥平均生物可利用性磷含量为50.33 ± 12.62 mg/kg,较前者低21.93 mg/kg。底泥生物可利用性氮磷比在5组中均小于0.5,而无青苔塘平均较有青苔塘高26.32%。低氮磷比会抑制浮游藻类的繁殖,而青苔则对低氮及低氮磷比环境具有较强的适应能力,因此,在养殖开始时,底泥低氮及低氮磷比的条件使得浮游藻类在与青苔的初期生态位竞争中处于劣势,即使检测到的浮游藻类OTUs数量高于青苔繁殖体,也不能使其在上述条件下成为优势种。另外,对青苔繁殖体的检测发现,其广泛存在于有青苔塘、无青苔塘及水源的水体和底泥中,即使清塘、晒塘依然检测到繁殖体的存在,但清塘、晒塘能够减少青苔繁殖体的数量。因此,单独依靠生石灰或漂白粉清塘并不能完全杜绝青苔的发生,但可以作为一个辅助防控措施,而通过调控养殖系统的生物可利用氮含量及氮磷比左右种间生态位竞争则是一个值得深入研究的、有前景的青苔防控方向。     

华中地区4座不同类型水库浮游植物的群落结构和多样性

2006-2008年对湖北境内4座水库的大型浮游植物群落结构和多样性进行周年研究。4座水库共鉴定出浮游植物215种,从组成来看,均属于硅藻-绿藻型,蓝藻含量居第3位。蓝藻主要分布在1倍透明度(SD)以上的水层,硅藻主要分布在1SD~2SD之间水层,其余各门藻类基本上集中分布在2SD以上水层,绿藻门中的栅藻(Scenedesmus),裸藻门中囊裸藻(Trachelomonas)则广泛分布于深水层中。不同水层的浮游植物密度差异很大,表层与底层的差异可达2倍以上。各水库浮游植物年平均密度和生物量分别为:金沙河123.2×104 cells.L-1,1.283 mg.L-1;道观河258.6×104 cells.L-1,3.335 mg.L-1;徐家河210.5×104 cells.L-1,2.740 mg.L-1;桃园河221.3×104 cells.L-1,3.088 mg.L-1。浮游植物生物量的水层分布除道观河为表层>SD>2SD>3SD>底层,其余3座水库均为SD>表层>2SD>3SD>底层。从水库之间来看,金沙河的Shannon-Wiener多样性指数(H)、Pielou均匀度指数(J)与其他3座水库各指数之间的差异均达到了极显著水平(P<0.01),而道观河、徐家河、桃园河两两之间差异不明显。TN与浮游植物呈负相关,而TP与浮游植物呈正相关,但未达到显著水平(P>0.05)。水体的营养水平不同是4座水库浮游植物群落结构差异的主要原因。本研究旨在为水库渔业资源的合理利用,以及水库环境保护与水质评价等相关研究积累基础资料。     

Principal component analysis of interactions between fish species and the ecological conditions in fish ponds: I. Phytoplankton*

Abstract. Interactions between fish species and their effect on the ecological conditions in the fish pond were studied in ten ponds of 0.1 ha each. The ponds were stocked with bottom-feeding fish: common carp, Cyprinus carpio L., and male hybrid tilapia Oreochromis niioticus (L.) x O. aureus (Steindachner). and a filter-feeder: silver carp, Hypophthalmichtys molitrix (Valenciennes), in various combinations. This paper deals with the effect of different assemblages of these fishes on the phytoplankton populations in the ponds. A Principal Component Analysis of the data showed that only 20% of the phytoplanktonic variability is accounted for by the fish combination present in the pond (treatment). The first principal component (PCI) groups the species of phytoplankton which responded to treatment. This component is formed by small size species; Scenedesmus spp., small Chlorophytes (mainly Chlorella), Selenastrum minutum, Ankistrodesmus setigerus, Merismopedia minima and Diatoms of the order Pennales. The presence of silver carp led to an increase in total phytoplankton numbers, concurrently with a decrease in their dominant size. This was due to the predominance in the water of the small size species of the PCI group, which could not be retained by the gill filtering apparatus of the fish. Reduction in zooplankton abundance by silver carp also contributed to this situation. The presence of bottom-feeding fish resulted in a decrease in total phytoplankton numbers, and in the importance of the small-size species of the PCI group, and hence in the dominance of larger algae. The interactions between these two trophic types of fish and algae size are discussed.     

Nutrient dynamics and plankton cycles in artificial ponds used in the production of oyster Ostrea edulis L. spat

The European flat oyster, Ostrea edulis L., has been successfully cultured in Cork Harbour on the south coast of Ireland, using non-tidal, man-made ponds for over 20 years. Broodstock placed in ponds spawn and the released larvae grow and settle on mussel shell cultch. This study investigates the nutrient dynamics and plankton cycles that occur from the time the ponds are filled. The incoming water to the ponds, when filled in May-June, is usually nutrient rich, with high numbers of diatoms. The nutrients become depleted quickly and the phytoplankton becomes dominated by smaller algal species, particularly flagellates and by dinoflagellates. Following mussel shell addition, orthophosphate levels increase and this pulse in nutrients is generally followed by an increase in microplankton, particularly Chlorella species. This increase often reaches bloom proportions and, if so, ponds are flushed. This addition of water increases the nutrient level and changes the phytoplankton composition, usually by introducing new dinoflagellate and diatom species.     

Effects of tilapia (Oreochromis niloticus L.) stocking and artificial feeding on water quality and production in rohu–common carp bi‐culture ponds

Previous research showed that stocking 1.5 rohu (Labeo rohita) and 0.5 common carp (Cyprinus carpio) m⁻² yields the highest production in small holder ponds in Bangladesh. The present study looked into the effects of additional stocking of Nile tilapia (Oreochromis nilotica) in fed or non‐fed ponds on water quality and fish production. A low, additional stocking density of 0.2 Nile tilapia m⁻² was tested. All treatments were executed in triplicate in 100 m² ponds and the duration of the experiment was 4.5 months. The results showed that tilapia addition increased nutrient concentrations and reduced total suspended solid concentration and phytoplankton biomass (P<0.05). Tilapia stocking resulted in additional production without affecting the growth and production of rohu and common carp. Supplemental feeding increased the nitrogen and phosphorus concentrations, phytoplankton availability and the growth and production of rohu and common carp (P<0.01). The combination of supplemental feeding and tilapia stocking resulted in a higher net yield than the other treatments (P<0.05). Stocking 1.5 rohu, 0.5 common carp and 0.2 tilapia m⁻² in fed‐ponds is a good culture combination for polyculture farmers in South Asia.     

绍兴市凡纳滨对虾围垦滩涂养殖池塘的理化环境和浮游植物

2016年和2017年分别调查了位于浙江省绍兴市滨海新区的12口凡纳滨对虾围垦滩涂养殖池塘内的理化环境和浮游植物。结果显示:池塘内盐度变化范围为0~2,溶氧为6.2~13.9 mg/L,pH为7.5~9.8,总氨氮(TAN)为0.00~0.72 mg/L,亚硝酸盐氮(NO_2~--N)为0.00~1.70 mg/L,硝酸盐氮(NO_3~--N)为0.18~4.77 mg/L,总氮为1.74~6.08 mg/L,总磷为0.20~2.72 mg/L,总有机碳为1.88~42.57 mg/L,C/N为10~39。池塘内浮游植物种类隶属6门、24科、42属,其中蓝藻和绿藻为优势种。浮游植物生物量为(0.15~2.30)×107cell/L,叶绿素a(Chl.a)为2.62~37.24μg/L。Chl.a与蓝藻生物量显著正相关。NO_2~--N和NO3--N均与pH显著负相关。初步分析认为高pH可能是导致2016年池塘养殖凡纳滨对虾死亡率较高的重要原因,因此采取措施控制蓝藻生物量和水体的p H应有助于提高对虾养殖的存活率。     

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。     

池塘底泥生物组成的季节性变化对刺参食物来源的影响

为分析刺参养殖池塘底泥生物组成的季节变化及其对刺参食物来源的影响,本研究于2012年5—12月以16:1(n-7)/16:0及EPA作为硅藻的特征脂肪酸标志,20:4(n-6)作为褐藻的特征脂肪酸标志,DHA及DHA/EPA作为鞭毛藻或原生动物的特征脂肪酸标志,18:1(n-7)及奇数碳和支链脂肪酸(oddbr FAs)作为细菌的特征脂肪酸标志调查了荣成靖海湾刺参养殖池塘底泥和刺参脂肪酸组成的季节性变化特征。结果显示,硅藻、褐藻、多种异养细菌及鞭毛藻或原生动物为底泥的主要组成生物,且各类生物组成的季节变化显著,其中硅藻的特征脂肪酸16:1(n-7)/16:0及EPA最高值出现在冬季,褐藻的特征脂肪酸20:4(n-6)含量为秋季最高,细菌的特征脂肪酸18:1(n-7)及(oddbr FAs)最高值出现在夏季,鞭毛藻或原生动物的特征脂肪酸DHA含量为冬季最高。相关性分析显示,刺参食物中的硅藻、鞭毛藻或原生动物和细菌主要来源于底泥。研究表明,刺参养殖池塘底泥中主要生物组成季节性变化显著,进而引起刺参食物来源的季节性变化。     

Inorganic nitrogen addition in a semi‐intensive turbot larval aquaculture system: effects on phytoplankton and zooplankton composition

A nitrogen manipulation experiment was conducted in a semi‐intensive outdoor system where turbot larvae feed on copepods. Nitrogen addition is hypothesized to stimulate a cascade reaction increasing phytoplankton biomass, copepods’ productivity and larval fish survival. Triplicates were established for three treatments: a control with no additional nitrogen, a pulsed dose where nitrogen was added in three doses over time and a full dose where all nitrogen, equal to the total of the pulse dose treatment, was added initially. In the control, chlorophyll a averaged 3.3 ± 1.5 μg L^?1 and phytoplankton was dominated by diatoms, while the pulsed and full dose treatments showed chlorophyll a at 28.6 ± 9.9 and 47.7 ± 10.0 μg L^?1, respectively, with dinoflagellates as the main phytoplankton group. Due to photosynthesis, pH increased >9 in both the nitrogen treatments compared to the control (8.5). Potential toxic dinoflagellates, including Alexandrium pseudogonyaulax and Prorocentrum spp., became dominant in the nitrogen treatments and might have arrested zooplankton recruitment. Laboratory experiments with a toxic strain of A. pseudogonyaulax proved that Acartia tonsa reproduction and naupliar survival were affected negatively at realistic fish tank concentrations of 100 and 20 cells mL^?1, respectively. Compared to the control, pulsed and full dose treatments reached higher copepod biomass and showed a shift over time in species composition from Centropages hamatus to Acartia spp. However, high pH levels and dinoflagellate blooms had a negative effect on larval fish survival, suggesting management improvements on water quality and separation between copepods and fish production tanks.     

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.     

Physical and chemical characteristics of sediments in catfish, freshwater prawn and carp ponds in Thailand

Sediment samples were collected from 42 catfish (Clarias hybrid) ponds, 40 freshwater prawn (Macrobrachium rosenbergii) ponds and 18 carp (Puntius spp.) ponds in Thailand. Regression analysis revealed that pond age (1–30 years) was not a major factor influencing the physical and chemical composition of pond sediments. Sediment depth, F+S horizon thickness and bulk density of S horizon were greater (P<0.05) in carp ponds than in catfish and prawn ponds. This occurred because sediment was removed from catfish and prawn ponds more frequently than from carp ponds. Total carbon, organic carbon and total nitrogen concentrations were greater (P<0.05) in carp ponds than prawn and catfish ponds. Few ponds had sediment organic carbon concentrations above 3%, and carbon:nitrogen ratio values did not differ (P>0.05) among ponds for the three species. Total phosphorus and other sediment phosphorus fractions increased in the order prawn ponds, carp ponds and catfish ponds. Sediment sulphur concentrations also increased in the same order. There were no differences in major or minor nutrient concentrations in sediment that would influence aquacultural production. Although there were significant correlations (P<0.05) between various sediment quality variables, no single variable or group of variables would be useful in estimating sediment quality. Pond bottom management practices used by producers in Thailand included drying of pond bottoms between crops, liming, tilling and periodic sediment removal. These practices have maintained relatively good bottom quality. They should be continued in Thailand and adopted in other places.     

Determination of the phosphorus fertilization rate for bluegill ponds using regression analysis

Pond fertilization studies usually are restricted by availability of ponds forcing researchers to limit treatments to maintain adequate replicates for statistical analysis. Data from a wide range of fertilizer rates applied over a single season in un‐replicated ponds were treated using regression analysis to establish the optimum phosphorus application rate for bluegill (Lepomis macrochirus) ponds. The response to phosphorus fertilization conformed to a saturation model (R²=0.92). Bluegill production increased with greater fertilization rate up to 3 kg P₂O₅ ha^?1, but production was similar (501–558 kg ha^?1) at rates of 3–7 kg P₂O₅ ha^?1. The observation that 3 kg P₂O₅ ha^?1 per application was adequate phosphorus fertilization for bluegill ponds with sufficient nitrogen agrees closely with the usual recommendation of 4 kg P₂O₅ ha^?1 per application. Results of this research also revealed that nutrient assessment in bluegill ponds can be based on total nitrogen and total phosphorus analyses, and Secchi disk visibility may be used as an index of plankton abundance.     

The use of high rate algal ponds for the treatment of marine effluent from a recirculating fish rearing system

A high rate algal pond (HRAP) system was used to treat effluent from a recirculating sea water aquaculture system in southern France. Dicentrarchus labrax L. were farmed at a high density, with effluents containing an average of 10 mg L^?1 dissolved inorganic nitrogen (DIN) and 1.3 mg L^?1 reactive phosphorus (RP). On a yearly basis, the algal pond removed 59% of the dissolved nitrogen and 56% of the phosphorus input, which was converted into 3.3 kg DW m^?2 algae. Green macroalgae were dominant throughout the year and the algal biomass mirrored the seasonal changes in daily irradiance and temperature. This first year study supports the possibility of treating marine aquaculture wastes using HPAPs, although conditions will have to be found to mitigate the strong influence of climate on the algal community during winter. During the more temperate season, only 150 m² of treatment ponds would be necessary to remove the nutrients produced by 1 ton of fish. Treated water was characterized by a high pH, elevated levels of dissolved oxygen (midday value) and low concentrations of nutrients and suspended solids. The absence of toxic phytoplankton meant that the water could be recycled through the farm tanks.