Intensive Fishpond Research Articles

Experimental Biology in Conflict Resolutions: The Case of Pelicans and Cormorants in Israel

In Israel, which is a bottleneck for some six hundred million migrating birds, the drainage of the Hula Lake in the north resulted in serious conflicts between fish-eating birds and the intensive fish farming and agriculture that became established on the reclaimed land. Implementation of various deterrence methods, including lethal control, failed to solve these conflicts. We followed the concept that only by understanding the biology of the organism in question could the tools (indications) for effective and sustainable management be devised that would solve such conflicts while helping the preservation of natural assets such as wetlands and their inhabitants. We demonstrated this concept in the solutions reached in the case studies of pelicans and cormorants and their interactions with intensive commercial fish ponds. We studied the physiological condition, food preference and energy demands, and ecological constraints of Great White Pelican Pelecanus onocrotalus, Great Cormorant Phalacrocorax carbo and Pygmy Cormorant Microcarbo pygmeus. As a result, we suggested different management solutions that are currently implemented with the full cooperation of the fishermen and the nature preservation authorities. Based on assessment of visual acuity to detect and catch fish under water Great Cormorants were effectively pushed towards Lake Kinneret where they could hunt more profitable fish than in the turbid fish ponds. The established roosts there were not controlled such as to lead the birds away from the fishponds. In case of the pelicans, part of the drained Hula valley was reflooded and extra fish was provided. Both measures effectively reduced the damage at the fish farms. We have shown that such solutions are economically helpful for fishermen and enable the preservation of the wetland habitat.

Sediment microbiota in polyculture of shrimp and fish pattern is distinctive from those in monoculture intensive shrimp or fish ponds

Sediment microbial community plays a crucial role in aquaculture ecosystem. In aquaculture practice, rather than monoculture intensive shrimp (IS) or intensive fish (IF) patterns, polyculture of shrimp and fish (PolySF) pattern leads to a more reliable production. However, knowledge is still limited about the characteristics of sediment microbiota and its potential functions in the PolySF ponds compared to monoculture patterns (IS and IF). Herein, we collected sediment samples from these three patterns in seven cities to evaluate microbial variations among patterns. The highest oxidation reduction potential (ORP), total phosphate (TP) and total organic carbon (TOC) were detected in the PolySF pattern, representing a relatively less anoxic environment, while the highest iron (Fe) was detected in IS pattern. Proteobacteria was the most abundant phylum among three patterns, followed by Bacteroidetes and Chloroflexi. The microbial alpha diversity in the PolySF was higher than those in the IF, but lower than those in the IS. Microbial communities of these three patterns were significantly distinct from each other, and 23 distinguished taxa for each pattern were further characterized. In additional, the relative abundances of genes involved in nitrogen metabolism, fatty acid biosynthesis and carbon fixation pathways were markedly shifted. Moreover, ORP, TOC and Fe were the shaping factors for sediment microbiota, which significantly varied among three patterns. Collectively, these findings demonstrated that sediment microbial communities in the PolySF were distinctive from those in the IS and IF, which enlarged our understanding for the underlying mechanism of advances in the PolySF pattern from ecological perspective.

Status of Water Quality in Fishponds Surrounding Manila Bay

Fishponds around Manila Bay contributed an average of 41.19% of the total aquaculture production in the country. However, massive productions entail the intensification of ponds, which resulted in water quality deterioration. In 2016, Opinion et al. reported water quality in the aquaculture farms around the bay but does not include the other significant parameters required to be monitored, as stated in the DENR AO (2016). Thus, this study investigated the status of water quality in different pond systems surrounding Manila Bay. Extensive, semi-intensive, and intensive fishponds from adjoining provinces of Cavite, Pampanga, Bataan, and Bulacan were monitored throughout the rearing period. Results showed that levels of NH3-N (0.90 mg/L – 2.35 mg/L) and PO4-3 (1.02 mg/L – 2.42 mg/L) were not suitable for the culture of fish. Nevertheless, NO3-N, NO2-N BOD, TSS, DO, pH, and temperature were within the safe levels. Furthermore, results suggested that there should be a regular monitoring of water quality to regulate and manage fishponds surrounding the bay. Finally, strict compliance of the Code of Good Aquaculture Practices (GAqP) must be imposed to achieve water quality standards.

Screening of a high bioflocculant‐producing bacterial strain from an intensive fish pond and comparison of the bioflocculation effects withRhodococcus erythropolis

A high bioflocculant-producing bacterial strain BX-13 isolated from an intensive fish pond by multiple subcultures and measured through primary screening and rescreening using kaolin. The strain BX-13 was identified to belong to the same branch as Bacillus subtilis by morphological, physiological and biochemical, 16S rDNA gene sequencing, Blast homology search and multiple sequence alignments. The bioflocculation potential of BX-13 and Rhodococcus erythropolis was compared, using water from the intensive pond where BX-13 was isolated. The results showed the number of colonies in the BX-13 treatment was higher than that of the R. erythropolis treatment from day 10 to the end of the experiment (p < 0.05). The numbers of both BX-13 and R. erythropolis in the water body peaked on day 15, with 2.23 × 107 cfu/L and 9.90 × 106 cfu/L respectively. The bioflocculation volume (BFV) in water increased and then stabilized in both BX-13 and R. erythropolis treatments. The BFV in BX-13 peaked on day 25 (52.13 ml/L) and R. erythropolis peaked on day 30 (22.63 ml/L). At the end of the experiment, the BFV of the BX-13 treatment was higher than the R. erythropolis treatment (p < 0.05). In conclusion, B. subtilis BX-13 has a very strong flocculation effect, and merits further research into its application for water quality regulation in aquaculture systems.

Design and performance of a novel rice hydroponic biofilter in a pond-scale aquaponic recirculating system

Aquaponics is the integration of recirculating aquaculture and hydroponic systems which is considered to be an innovative, eco-friendly and sustainable food production technology. In this study, a special design of hydroponic biofilter that integrated constructed wetlands and floating-raft rice hydroponics was constructed to treat the nutrient rich effluents from the intensive fishpond and to establish an aquaponic system on pond scale. The treatment efficiencies and food production potential of the new rice hydroponic biofilter was evaluated after determining the key operating parameters. As the results, overall nutrient removal efficiency was optimized at hydraulic load rate (HLR) of 0.58 m.d−1 and air-to-water ratio of 2:1. The average removal efficiencies of total ammonia nitrogen (TAN), total nitrogen (TN), total phosphorus (TP) and chemical oxygen demand (CODMn) from fishpond wastewater were in the range of 33.75–34.31%, 59.21–64.53%, 68.43–73.75% and 71.66–74.37%, respectively. Meanwhile, hydroponic rice grew well in the biofilter and gained a yield of 7 127 kg.ha−1. These results probably implied that the novel rice hydroponic biofilter exhibited efficient effluent treatment and presented as a viable alternative for the food production in a pond-scale aquaponics recirculating system.

Intensive fish ponds as ecological traps for dragonflies: an imminent threat to the endangered species Sympetrum depressiusculum (Odonata: Libellulidae)

The concept of ecological traps, in which animals settle in low-quality habitats, is well-established. Dragonflies are a good model for investigating the effects of ecological traps because their habitat selection process can be directly observed. Unfortunately, most such studies focus on oviposition on artificial materials, such as car surfaces, gravestones, and plastic foils, which results in complete mortality of the clutch. It remains unclear to what extent intensive fish ponds, ubiquitous in the European agricultural landscape, act as ecological traps for some dragonfly species and how they influence their vulnerability. We investigated the effects of putative ecological traps on the threatened dragonfly Sympetrum depressiusculum and the common closely related species S. sanguineum in a Central European agricultural landscape. Observations of adult behavior were used to parameterize GLMs examining the attractiveness of five fish ponds (three fish breeding and two intensive) to each species. We also counted exuviae at each pond as a measure of each species’ survival. We used GLMMs to determine which factors affected selection of oviposition sites and the environmental factors resulting in ecological traps for each species. All five ponds were attractive to ovipositing pairs of both species, although they were largely unsuitable for subsequent development (four for S. depressiusculum and two for S. sanguineum). Our results provide evidence that intensive fish ponds act as ecological traps for both species. We believe that cutting of the vegetation surrounding trap habitats could be an effective way to decrease their attractiveness to a wide range of dragonfly species.

The unnatural history of Kāne'ohe Bay: coral reef resilience in the face of centuries of anthropogenic impacts.

Kāneʻohe Bay, which is located on the on the NE coast of Oʻahu, Hawaiʻi, represents one of the most intensively studied estuarine coral reef ecosystems in the world. Despite a long history of anthropogenic disturbance, from early settlement to post European contact, the coral reef ecosystem of Kāneʻohe Bay appears to be in better condition in comparison to other reefs around the world. The island of Moku o Loʻe (Coconut Island) in the southern region of the bay became home to the Hawaiʻi Institute of Marine Biology in 1947, where researchers have since documented the various aspects of the unique physical, chemical, and biological features of this coral reef ecosystem. The first human contact by voyaging Polynesians occurred at least 700 years ago. By A.D. 1250 Polynesians voyagers had settled inhabitable islands in the region which led to development of an intensive agricultural, fish pond and ocean resource system that supported a large human population. Anthropogenic disturbance initially involved clearing of land for agriculture, intentional or accidental introduction of alien species, modification of streams to supply water for taro culture, and construction of massive shoreline fish pond enclosures and extensive terraces in the valleys that were used for taro culture. The arrival by the first Europeans in 1778 led to further introductions of plants and animals that radically changed the landscape. Subsequent development of a plantation agricultural system led to increased human immigration, population growth and an end to traditional land and water management practices. The reefs were devastated by extensive dredge and fill operations as well as rapid growth of human population, which led to extensive urbanization of the watershed. By the 1960’s the bay was severely impacted by increased sewage discharge along with increased sedimentation due to improper grading practices and stream channelization, resulting in extensive loss of coral cover. The reefs of Kāneʻohe Bay developed under estuarine conditions and thus have been subjected to multiple natural stresses. These include storm floods, a more extreme temperature range than more oceanic reefs, high rates of sedimentation, and exposure at extreme low tides. Deposition and degradation of organic materials carried into the bay from the watershed results in low pH conditions such that according to some ocean acidification projections the rich coral reefs in the bay should not exist. Increased global temperature due to anthropogenic fossil fuel emmisions is now impacting these reefs with the first “bleaching event” in 1996 and a second more severe event in 2014. The reefs of Kāneʻohe Bay have developed and persist under rather severe natural and anthropogenic perturbations. To date, these reefs have proved to be very resilient once the stressor has been removed. A major question remains to be answered concerning the limits of Kāneʻohe Bay reef resilience in the face of global climate change.

Effect of water aeration and nutrient load level on biomass yield, N uptake and protein content of the seaweed Ulva lactuca cultured in seawater tanks

The effects of 16 different combinations of nutrient load and agitation on yield, nutrient uptake and proximate chemical composition of the seaweed Ulva lactuca cultured in tanks were evaluated. Intensive fishpond outflow passed through seaweed tanks at four nutrient loading levels and four water agitation combinations of water exchange, bottom aeration and frequently changing water levels (an accelerated tide regime). Specific results from these outdoor experiments were examined further under controlled conditions in laboratory experiments. Agitation treatments affected the performance of U. lactuca only under TAN (\({\text{NH}}_{3} + {\text{NH}}^{ + }_{4} \)) load levels below 4 g N m−2 day−1; biofiltration of TAN was the parameter most affected. Biomass yields at each of the four nutrient loading levels were not significantly different between the agitation treatments. Protein content increased significantly with increasing nutrient loading. The agitation treatments had a slight effect on seaweed protein content only at the lowest nutrient loading levels. There were no significant differences in dissolved oxygen concentration, pH, and temperature among the agitation treatments at all nutrient loading levels. Under laboratory conditions, growth rates, protein content, and photosynthetic and biomass yield of the seaweed were affected by water velocity under low nutrient concentrations. It is concluded that the effect of air agitation under the conditions of these experiments was not directly related to photosynthesis, excess dissolved oxygen, or carbon limitation, but to the diffusion of macro nutrients from the water to the seaweed. Therefore, once nutrient concentrations are high enough (above about 4 μM of TAN with the other nutrients in their corresponding proportions), aeration per se is not essential for effective growth and biofiltration by seaweeds.

Experiments on the Nutrient Removal and Retention of an Integrated Pond System

A combined intensive-extensive fishpond system developed for the purification and re-use of intensive fishpond effluent water was studied during a three-year experimental period. The investigated pond system consists of five small-size intensive culture ponds of 1 ha total water surface area with 1.5 m water depth and a 20 ha extensive culture pond with 1.0 m average water depth. The water was recirculated between the intensive and extensive ponds with around 60 days retention time in the extensive treatment pond.Carbon, nitrogen and phosphorus budget and water purifying capacity were described and evaluated by means of regular measurements of nutrient concentrations in the water and sediment. During the three-year test period, 81.5% of organic carbon, 54.7% of nitrogen and 72.2% of phosphorus were retained by the system as a percentage of the total input of each nutrient. A significant amount of the total nitrogen input was removed by the harvested fish, which was much higher than in traditional fishponds or intensive fish culture systems. The efficiency of nutrient removal is clearly indicated by the 27.3% nitrogen assimilation.Only a small percentage of the total nutrient input was discharged into the environment during fish harvest, which was 9.0% for organic carbon, 13.2% for nitrogen and 12.1% for phosphorus. The combination of intensive and extensive fishponds with water recirculation resulted in significant reduction of nutrient discharge into the surrounding aquatic environment, primarily due to the high nutrient processing and retention capacity of the extensive fishpond ecosystem.

A novel three-stage seaweed (Ulva lactuca) biofilter design for integrated mariculture

Seaweed biofilters have proven their usefulness in the treatment of fishpond effluents. However, their performance poses a dilemma: TAN (Total Ammonia N) uptake rate – and with it seaweed yield and protein content – is inversely proportional to TAN uptake efficiency. The ideal for a seaweed biofilter performance would be a high uptake rate together with high uptake efficiency. The novel three-stage seaweed biofilter design described here has solved this dilemma. The design used the finding that the performance of seaweed ponds depended on the flux of TAN through them, and that therefore effluents with reduced TAN concentration could provide the seaweed with a high TAN flux if the water flow increased proportionally. Effluents from a seabream fishpond were passed through a series of three successively smaller (25, 12.5 and 6.25 m2, respectively) air-agitated Ulva lactuca ponds. The diminished inflow TAN concentrations to the second and third ponds of the biofilter system were compensated for by the increased water exchange rates, inversely proportional to their sizes. The biofilter performance was evaluated under several TAN loads. TAN was efficiently removed (85–90%), at a high areal rate (up to 2.9 g N m-2 d-1) while producing high protein U. lactuca (up to 44% dw) in all three stages, although with mediocre yields (up to 189 g fresh m-2 d-1). Performance of each seaweed biofilter pond correlated not with TAN concentration, but with areal TAN loads. The novel three-stage design provides significant functional and economic improvements in seaweed biofiltration of intensive fishpond water.

A semi-recirculating, integrated system for the culture of fish and seaweed

Abstract Biofiltration allows for environmentally sustainable mariculture. An intensive, biofiltered recirculating integrated system producing fish and seaweed on a semi-commercial scale was evaluated with respect to production and to nutrient and heat budgets. The system consisted of abalone (Haliotis discus hannai) and sea urchin (Paracentrotus lividus) tanks, an intensive fishpond (Sparus aurata), and a three-stage Ulva lactuca biofilter, which cleaned and recirculated 50% of the effluent back to the fishpond. To preserve water heat, the shellfish and fishpond units were both covered with greenhouses; the biofilter unit was covered with a greenhouse only during winter. Seaweed yield was variable and averaged 94 and 117 g m−2 day−1 (fresh weight) in periods with and without greenhouse cover, respectively. Protein content of U. lactuca averaged above 34% of dry weight. The biofiltration of only 50% of the water through the seaweed biofilter reduced the export of dissolved nutrients to the environment by nearly 30%. Peak ammonia excretion by the morning-fed fish coincided with maximum seaweed light-dependent ammonia uptake and concentrations of ammonia in the fishpond remained within nontoxic limits. Also, daytime photosynthesis of U. lactuca (uptake of CO2) met fish respiration (production of CO2), thus balancing fishpond pH levels within safe limits regarding ammonia toxicity. Daytime oxygen demand by the fish was partially met by the photosynthetically generated oxygen. Before covering the biofilter with a greenhouse, it lost much heat, reducing the temperature in the fishpond. Following the greenhouse covering of the biofilter, heat loss ceased and consequently the fishpond temperature was raised. Recirculation through the biofilter improved system sustainability; it reduced water use, lowered negative environmental impact, and maintained stable and safe water quality conditions in the fishpond.

Experiments on the nutrient removal and retention of a pond recirculation system

A combined intensive-extensive fishpond system developed for the purification and re-use of intensive fishpond effluent water was studied during a three-year experimental period. The studied pond system consists of five small-size intensive culture ponds (1 ha each and 1.5 m deep), and a 20 ha extensive culture pond with 1 m average depth. The water was recirculated between the intensive and extensive ponds with retention time of about 60 days. Carbon, nitrogen and phosphorus budget and water purifying capacity are described and evaluated by regular measurements of nutrient concentrations in the water and sediment. During the three-year test period 81.5% of organic carbon, 54.7% of nitrogen and 72.2% of phosphorus were retained by the system. A significant amount of the total nitrogen input was removed by the fishery. A small percentage of the total nutrient input was discharged into the environment during fish removal. The combination of intensive and extensive fishponds with water recirculation resulted in a significant reduction of nutrient discharge to the surrounding aquatic environment.

Modeling approach of nitrogen and phosphorus exchanges at the sediment–water interface of an intensive fishpond system

The sediment–water interface in aquaculture ponds is both a sink and a source of various substances that are potentially toxic for cultured species. The sediment to water nitrogen and phosphorus exchanges were studied at the sediment–water interface in an intensive earthpond fish-farm on the French Atlantic coast. This was to define the contribution of diffusive fluxes to the total dissolved nitrogen and phosphorus produced during the 1997–1998 rearing period. Fluxes of particulate organic nitrogen (PON) and particulate phosphorus (PP) were modeled and validated using a set of observations. Diffusive fluxes were modeled using an empirical function of temperature based on in situ sediment porewater concentration profiles. An average of 15% of PON and 10% of PP, produced by fish food waste and fish faeces were sedimented in fishponds. Ammonia and phosphate diffusive fluxes (μmol m −2 h −1) were expressed as a function of temperature ( T). J mod NH 4 + =(0.144T+3.49)×10 −6 exp(0.11T+16.81) J mod PO 4 3− =(0.086T+1.8)×10 −6 exp(0.09T+15.76) PON and PP stocks in the sediment decreased during the summer and increased during the winter. However, sedimentation and mineralization–diffusion processes were approximately balanced over the 2-year period. Ammonia and phosphate diffusive fluxes accounted for only 1–4% and 4–15%, respectively, of the total dissolved nitrogen and phosphorus components produced during the rearing period.

Effect of different management practices on water quality of intensive tilapia culture systems in Israel

Commercial intensive aquaculture systems werebuilt and are managed in a somewhat differentway in each farm. To evaluate the effects ofseveral management procedures on water qualityin intensive fish ponds, data from severallocations, times and culture conditions indifferent farms were collected and are hereinanalyzed through multivariate statistics. Water quality in the intensive ponds depends onthe water entering, the biological processeswithin, and the water leaving the ponds. Areservoir used as source and sink water supplied theintensive ponds with higher organic loadingthan clear source waters, and its phytoplanktoncontent affected nitrogen cycling within theintensive ponds. The systems with a reservoirhad better water quality in the intensive pondsthan those with only clean source water. Within the ponds (1) compared to paddle-wheelaeration, aeration by pure oxygen increasedoxygen concentration, improved nitrificationand promoted decomposition that reduced organicloading. (2) In concrete ponds accumulation oforganic matter and development of anerobicconditions on the pond bottom was higher thanin the slippery plastic-covered ponds. (3) Allintensive ponds provided good growthconditions, tilapia biomass having relativelysmall influence on water quality. Only inpaddle-wheel aerated ponds did increased tilapiabiomass increased inorganic nitrogen compoundsand soluble phosphorus through excretion, andreduce organic nitrogen through a moreefficient removal of food particles. Water leaving the ponds removes matteraffecting water quality within the pond. (1)Draining sediments accumulated on the bottomavoided development of anaerobic conditionswhere denitrification and phosphorus liberationcan occur. (2) Water exchange removed particleswith nitrifying bacteria and algae that absorbnutrients. A high water exchange rate may havea negative effect from the water quality pointof view and from the extra costs incurred inenergy and feeds washed out. The processes described occur simultaneouslythroughout the culture period and shape waterquality dynamics in the ponds. This researchcontributed to the understanding of howmanagement procedures affect the differentphases of water quality dynamics in real-scaletilapia commercial intensive systems.

On the use of micro-electrodes in fish pond sediments

The surface layer of fish pond sediments is characterized by very high microbial activity. Oxygen uptake by the microbes at the sediment surface leaves little oxygen to penetrate the sediment. In marine and freshwater lake sediments, oxygen only penetrated a few millimeters. In this study, oxygen penetration into the sediment layer in fish ponds and simulated fish ponds was measured with an oxygen micro-electrode. Oxygen profiles determined with micro-electrodes showed that oxygen does not penetrate deeper than 1 mm under quiescent conditions in intensive and semi-intensive fish pond sediments. Sediment oxygen consumption (SOD) at approximately 25°C, calculated from measured oxygen profiles, ranged from 45 to 50 mg O 2/m 2 per h. Change in water temperature and the addition of formaldehyde showed that most of the oxygen consumption in the sediment surface layer is related to biological activity. Redox potential profiles of fish pond sediments measured with a micro-platinum electrode, showed reducing conditions conducive to sulfide formation at 2–4 mm below the sediment surface. Nitrate addition to the overlying water poised redox potential above 300 mV to a sediment depth of about 15 mm. Nitrate thus buffered the sediment–water interface against reducing conditions in the sediment and the possible diffusion of toxic reduced end products to the water.

Seaweed biofilters as regulators of water quality in integrated fish-seaweed culture units

The water-quality characteristics of a new system for the integrated culture of fish ( Sparus aurata L.) and seaweed ( Ulva lactuca L.) were examined. Seawater was recirculated between intensive fishponds and seaweed ponds. The seaweed removed most of the ammonia excreted by the fish and oxygenated the water. A model consisting of several tanks and a pilot consisting of two 100-m 3, 100-m 2 ponds were studied. In both, the metabolically dependent water-quality parameters (dissolved oxygen, NH 4 +-N, oxidized-N, pH and phosphate) remained stable and within safe limits for the fish during over 2 years of operation. The design allowed significant increases in overall water residence time (4.9 days), compared with conventional intensive ponds, and produced a high yield of seaweed in addition to the fish. The design provides a practical solution to major management and environmental problems of land-based mariculture.

Rates of organic carbon and nitrogen degradation in intensive fish ponds

Water quality in intensive aquaculture systems is to a large extent controlled by the microbial biodegradation of organic residues. The ability to simulate processes in such systems depends on the availability of data on the rates of these processes. The first order kinetic rate constants for both organic carbon and organic nitrogen degradation in fish ponds were evaluated. The rate constants were computed by either relating the measured rate of disappearance of the substrate concentration or by the comparison of the measured with a theoretically derived evolution pattern of organic carbon or nitrogen concentrations in model ponds. The organic carbon degradation rate constant was found to be 0.15/day. The organic nitrogen degradation rate constant was expected, theoretically to be about 0.06/day and was found experimentally to be in the range of 0.05–0.09/day. These values seem to be reasonable approximations for constantly aerated-mixed ponds, at a temperature range of 20–30 °C. Organic matter previously metabolized in anoxic sites at the pond (e.g. resuspended sediments), has a degradation rate of ca. 0.6/day, and can thus consume large amounts of oxygen in the water body.

Chronic toxicity of ammonia to juvenile gilthead seabream Sparus aurata and related histopathological effects

Effect of 20 days exposure of juvenile gilthead seabream (Sparus aurata) to elevated levels of ammonia on growth and survival was examined in a continuous flow system. Suppressed growth and reduced survival were observed at concentrations of 8.2 and 13 mg l−1 total ammonia‐N (0.5 and 0.7 mg l−1 un‐ionized ammonia‐N, respectively) and higher. The maximum acceptable toxic concentration (MATC) for growth was between 4.8 to 8.2 mg l−1 total ammonia‐N (0.3 and 0.5 mg l−1 un‐ionized ammonia‐N, respectively). Fish exposed to high ammonia levels (13 mg l−1 total ammonia‐N, 0.7 mg l−1 un‐ionized ammonia‐N) displayed clear signs of liver pathology. Existing evidence suggests that S. aurata is less sensitive to ammonia than other reported marine and freshwater fish.Under certain conditions ammonia concentration in the intensive fish ponds in Eilat may exceed the no observed effect concentration for S. aurata.

Ammonium uptake usingUlva (Chlorophyta) in intensive fishpond systems: mass culture and treatment of effluent

A vegetative clone ofUlva lactuca L. was selected for mass culture and nutrient uptake experiments with fish pond wastewater. Growth rates of over 55 g dry wt. d−1 per 6001(1 m2) tank were obtained. Growth rate was linked to stocking density, tank flushing rates and aeration induced thallus movement. The plants could not survive on the macronutrients provided by a weekly pulse of wastewater. A continuous supply of fish pond wastewater was required to maintain good growth rates. An ‘uncoupling’ of growth rate and thallus nitrogen content was observed. The plants were able to store nitrogen from a pulsed ammonium supply and allot the nitrogen reserves to new tissue growth. Plants with slower growth rates or a continuous supply of ammonium had higher thallus nitrogen content.Ulva efficiently removed up to 85% of the ammonium from fish pond wastewater in darkness or light independently of temperature fluctuations.

A total nutrient budget for an experimental intensive fishpond with circularly moving seawater

A total nutrient budget was measured in an experimental intensive fishpond with circularly moving seawater and a water retention time of 2 days. The pond was stocked with gilthead sea-bream, Sparus aurata. An important feature of this pond design was the significant reduction of the excess organic load of particulate matter by daily draining of the settled detritus. The major nutrient pathways consisted of fish excretion coupled with phytoplankton uptake. All inputs and outputs of phosphorus and nitrogen were measured daily over a 1-month period. Fish food accounted for more than 95% of the nutrient input, sustaining dense phytoplankton populations with up to 450 μg chlorophyll a l −1. Fish assimilated 21% of P and 26% of N inputs. On a monthly average, ca. 50% and 46% of the P and N inputs, respectively, were found in the particulate phase of the water column. This phase was dominated by a phytoplankton community which exhibited “bloom and crash” cycles due to microflagellate grazing. As the pond progressed from a bloom to a crash, the fractions of entering nutrients which ended in the particulate phase changed from 76% to 32% for P and from 63% to 34% for N. The drained settled detritus contained on average only 17% of the P and 10% of the N inputs. The outflow of dissolved matter contained 22% of P and 13% of N inputs. On a monthly average, surpluses (inputs minus outputs) of −10% for P and 5% for N were estimated in the budget, which balanced within experimental error. On a daily basis, however, the deviations from a balanced budget were occasionally larger, with surpluses ranging from −29% to 6% for P and from −3% to 8% for N. Attached macroalgal growth and decomposition are thought to be likely causes of these periodic deviations. The significant nonalgal conversion of dissolved total N into particulate N during phytoplankton crashes (as much as 20% of ammonia-N and 75% of dissolved organic-N) was probably due to uptake by bacteria and heterotrophic flagellates. Intensive bacterial activity, in particular sulphate reduction, was observed in the drained detritus.