Low Dissolved Oxygen Levels Research Articles

Response of Nile Tilapia reared at low dissolved oxygen level and challenged with Aeromonas hydrophila to dietary supplementation with different levels of Anise essential oil

This work was conducted to evaluate the effect of anise essential oil as a feed additive on growth performance and immunity of Nile tilapia (Oreochromis niloticus) exposed to two different challenges; reduced levels of dissolved oxygen (LDO) and/or infection with Aeromonas hydrophila. Juveniles were randomly distributed to six replicated experimental groups; groups 1, 2, and 3 were reared at normal levels of dissolved oxygen (NDO) (5 – 6 mg/l) and received 0, 1, and 2 ml/kg diet of anise essential oil, respectively. In addition, groups 4, 5, and 6 which were reared on LDO levels (2 – 3 mg/l) and received the same concentrations (conc.) of anise oil (0, 1, and 2 ml/kg diet, respectively). All groups were kept at a density of 30 fish/m3 and fed on a commercial basal diet (30% crude protein) for 60 days consecutively at rate of 3% body weight. Results cleared an enhancement of growth parameters of fish treated with anise oil, where final body weight, weight gain and average daily gain were increased and feed conversion ratio was decreased significantly than control groups even under hypoxic conditions. Moreover, groups that received anise oil showed stronger immunity against A. hydrophila infection synchronized with developed antioxidative capacity, where results indicated a significant increase in WBCs in all treated groups and globulin in a dose-dependent manner under hypoxic conditions. Additionally, using oil at a concentration of 2 ml/kg diet considerably raised superoxide dismutase (SOD) level under normal and hypoxic conditions and lowered the level of nitric oxide (NO) after challenge with bacteria at a concentration of 1 ml/kg diet at NDO and at 2 ml/kg diet at LDO.

Assessing Hydrological Dynamics during the Monsoon Season in the Hooghly River, West Bengal, India: An Evaluation of Comprehensive Pollution Index and Water Quality index

This study meticulously evaluates the water quality parameters of the Hooghly River during the period spanning 2022 to 2023, specifically during high tide, with a particular focus on the locales of Kamarhati, Panihati, and Khardah. A comprehensive analysis encompassed both physico-chemical and biological parameters. The application of Pollution indices, notably the Water Quality Index (WQI) and Comprehensive Pollution Index (CPI), elucidates the water quality status at the selected sampling locations. Elevated E. coli levels (Kamarhati: 10000, Panihati: 15000, Khardah: 20000), turbidity, and total suspended solids exceeded WHO and BIS standards, categorizing the river as slightly polluted (CPI: Kamarhati-0.67, Panihati-0.68, Khardah-0.59), rendering the water unsuitable for consumption (WQI > 100). Low dissolved oxygen levels (1.9-2.4 mg/l) and significant microbial contamination (coliform: 10000-20000 MPN) underline the urgent need for targeted interventions. While pH, temperature, and DO levels suggested a stable aquatic environment, elevated TDS, TSS, and E. coli concentrations signify potential pollution sources, necessitating immediate water treatment. Moderate levels of BOD and COD indicate a manageable organic pollutant load, and nitrate and nitrite within permissible limits are positive.

Water quality and the presence of metals in crustaceans (Sartoriana spinigera) and mollusks (Pila globosa) close to an urban waste landfill in Kodda at Gazipur

Degradation of water and sediment quality along with other aquatic ecosystem components, due to urban waste is a significant concern that demands attention. Despite of the multifaceted use of the Konabari area within the Gazipur City Corporation of Bangladesh, limited studies have assessed the health of the floodplain ecosystem adjacent to urban waste landfills in Kodda. This research focuses on evaluating water quality parameters and the presence of metals and metalloids in water, sediment, and biota (invertebrates) in the lowland floodplain near the Kodda municipal landfill in Gazipur district. In December 2022, thirteen composite samples, including water, sediment, crustaceans (Sartoriana spinigera), and mollusks (Pila globosa), were collected from the designated sampling site. Surface and sub-surface (0–15 cm depth) water were collected using a water sampler for water quality analysis, and the presence of heavy metal and metalloid content of the water, sediment, crabs, and mollusks were analyzed using an atomic absorption spectrometer. The results indicated dissolved oxygen concentrations ranging from 0.30 to 5.81 mg/l (mean 3.1±2.37 mg/l). Certain locations directly affected by waste discharge exhibited alarmingly low dissolved oxygen levels (~0.71 mg/l), coupled with elevated temperatures and phosphate (PO43−) content (2–7.4 mg/l). The scarcity of heavy metal concentrations (<0.0677 mg/l) in water may be attributed to the constant flow of water preventing metal accumulation in the flowing water. However, sediment analysis revealed significantly higher concentrations (mean±Sd) of Fe (15240±1211 mg/kg), Mn (1122±180 mg/kg), Cu (44±5.5 mg/kg), Cr (28±3.2 mg/kg), Ni (39±2.4 mg/kg), As (3.7±0.89 mg/kg), and Zn (72±3.95 mg/kg) compared to other studies in various locations. Crustacean (Crab) samples showed concentrations of Cr, As, Pb, Cd, Zn, and Cu exceeding recommended permissible limits. Pila globosa emerged as an effective ecological bioindicator of aquatic pollution, with concentrations of Cr, Mn, Ni, Cu, Zn, and Pd exceeding recommended limits. Despite eco-environmental indices suggesting low to moderate contamination, the heavy metals and metalloids study indicated degradation of ecosystem health triggered by urban waste discharge. Consequently, the study recommends proper waste treatment in landfills and their transformation from open dumps to scientifically managed controlled waste landfills. Ann. Bangaldesh Agric. 27(2):175-189

Mechanistic and Kinetic Consideration of the Photochemically Generated Oxidative Organic Radicals in Dissolved Black Carbon Solutions under Simulated Solar Irradiation.

The photochemically generated oxidative organic radicals (POORs) in dissolved black carbon (DBC) was investigated and compared with that in dissolved organic matter (DOM). POORs generated in DBC solutions exhibited higher one-electron reduction potential values (1.38-1.56 V) than those in DOM solutions (1.22-1.38 V). We found that the photogeneration of POORs from DBC is enhanced with dissolved oxygen (DO) increasing, while the inhibition of POORs is observed in reference to DOM solution. The behavior of the one-electron reducing species (DBC•-/DOM•-) was employed to explain this phenomenon. The experimental results revealed that the DO concentration had a greater effect on DBC•- than on DOM•-. Low DO levels led to a substantial increase in the steady-state concentration of DBC•-, which quenched the POORs via back-electron reactions. Moreover, the contribution of POORs to the degradation of 19 emerging organic contaminants (EOCs) in sunlight-exposed DBC and DOM solutions was estimated. The findings indicate that POORs play an important role in the photodegradation of EOCs previously known to react with triplets, especially in DBC solutions. Compared to DOM solutions, POOR exhibits a lower but considerable contribution to EOC attenuation. This study enhances the understanding of pollutant fate in aquatic environments by highlighting the role of DBC in photochemical pollutant degradation and providing insights into pollutant transformation mechanisms involving POORs.

The Impact of Anthropogenic Pollution on Tidal Water Quality in Mangrove Wetlands

Mangrove wetlands are vulnerable coastal ecosystems that provide critical habitats for aquatic life. Tai O is a popular tourist village on Lantau Island, Hong Kong, which is surrounded by mangrove wetlands with rich biodiversity; and this village is also famous for its traditional stilt houses. However, the untreated municipal sewage from some stilt houses is directly discharged into nearby tidal channels, potentially threatening health of the adjacent mangrove wetlands. In order to evaluate the anthropogenic impact on these wetlands and identify the potential sources of their pollution, this study aimed to evaluate spatial (at the sampling points) and temporal (during weekdays and weekends) differences in the quality of their tidal water, and examine relationships between the water quality and the density of the stilt houses. The results indicated that the water quality was worse during weekends. The ammonia concentrations in most samples exceeded the limits of the Hong Kong Water Quality Objectives, China’s Sea Water Quality Standards, and even the U.S. EPA criterion for fish reproduction. This high ammonia input could potentially adversely affect the mangrove ecosystem, underscoring the need for further comprehensive studies. Moreover, some of the weekend water samples had lower dissolved oxygen levels and were polluted by phosphate. Our Principal Component Analysis revealed that water quality was correlated with stilt house density, suggesting that anthropogenic inputs of untreated sewage was the major source of pollution. These findings highlight that nutrients released from human activities, particularly ammonia and phosphate, must be controlled for a better protection of mangrove wetland ecosystems.

Assessment of Water Pollution in the Korotoa River: Implications for Ecosystems and Human Welfare in Bogura, Bangladesh

This study presents a comprehensive evaluation of water quality in the Korotoa River, crucial to Bogura, Bangladesh, as it serves as a critical water supply for the city. Despite its significance, the river faces considerable pollution concerns from untreated pollutants emitted by urban and adjacent regions. The research attempts to analyze the level of water pollution and its repercussions on aquatic ecosystems and human usage. Through systematic water sample collection at numerous locations, the project examines physical and chemical features. Results, assessed against environmental criteria, indicate low dissolved oxygen levels and unsatisfactory water quality measures, particularly around confluence locations. The study exposes significant water pollution, necessitating immediate action to maintain aquatic life, ecosystems, and community well-being. Urgent pollution control actions are necessary to restore and preserve the Korotoa River’s natural balance in Bogura, emphasizing the need for education, monitoring, and research. The research provides insights for authorities and stakeholders to reduce pollution, sustaining the river’s critical role in the region’s biodiversity, agriculture, and human activities.

Engineering of the hypoxia-induced Pichia stipitis ADH2 promoter to construct a promoter library for Pichia pastoris.

Hypoxia-inducible promoters of a wide range of activities are desirable for fine-tuning gene expression in response to oxygen limitation, especially for the Crabtree negative yeast Pichia pastoris (Komagataella phaffii) with a high oxygen consumption rate in large-scale fermentations. Here we constructed a hypoxia-inducible promoter library for P. pastoris through error-prone PCR of Pichia stipitis ADH2 promoter (PsADH2). The library of 30 selected promoters showing 0.4- to 5.5-fold of the PsADH2 activity was obtained through high-throughput screening in microplates using the reporter yeast-enhanced green fluorescent protein. Two strong promoters, AM23 and AM30, were further characterized in shake flask cultures at high and low dissolved oxygen levels. They responded more sensitively to the low dissolved oxygen level, achieving a 4.6-, 7.9-fold and 3.6-, 7.7-fold higher fluorescence intensity and transcript level, respectively, than the wild-type PsADH2. Their hypoxia-inducible properties were confirmed with two additional reporters: β-galactosidase and Vitreoscilla hemoglobin, to demonstrate the broad applicability of the promoter library. During the typical fermentation process in shake flasks, the promoter AM30 showed strong expression with cell growth and decreased oxygen levels, without any additional chemical inducers or operations. Since the potent industrial host P. pastoris is recognized as an easy to scale-up system, it is reasonable to expect that the obtained hypoxia-inducible promoter library may have great potential to enable convenient regulation of gene expression under industrial fermentations which are usually run under oxygen limitation due to high cell density cultivations.

Hydrochemical Characteristics and Self-Purification Potential of Iyiechu Stream in Okigwe Area, Southeastern Nigeria

Iyiechu stream is a small tropical urban stream that receives both domestic and industrial wastes. The self-purification potential of the stream was determined by evaluating its deoxygenation and reaeration rate coefficients. The methods of study used include dissolved oxygen (DO) measurements, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) tests as well as measurements of hydrological parameters. Deoxygenation rate of 0.20 to 0.42/day were obtained indicating very swift depletion of oxygen in the stream probably as a result of domestic sewage input. The reaeration rate coefficients ranged from 0.01 to 0.84 day and these values suggest deep and slow moving streams. The measured DO values are quite low, indicating high deoxygenation reaction in the stream and minimal dissolved oxygen contribution from other sources such as algal photosynthesis. Spatially, about 66.66% of the stream is dominated by deoxygenation reaction. The chemical oxygen demand ranged from 20 to 40 mg/l. These values are relatively high and show that the process may be partly responsible for the low dissolved oxygen levels in the stream. However, the stream is capable of re-attaining its optimum dissolved oxygen level within a flow time of 0.84 day (20hrs 16minutes) in the rainy season. Thus, a flow time much greater than 0.84 day (20hrs 16minutes) would be required during the dry season. These flow times suggest that the stream has poor self-purification potential.

Multibranch Modelling of Flow and Water Quality in the Dhaka River System, Bangladesh: Impacts of Future Development Plans and Climate Change

Long-term development and pollution clean-up plans are a continuing feature of megacities such as Dhaka, Bangladesh. Bangladesh needs to deal with a legacy of past pollution and manage current pollution from a rapidly expanding economy. Surveys in the rivers around Dhaka show extremely high pollution and very low dissolved oxygen levels, with subsequent ecological impacts. Millions of people are not on public treatment of effluents and thousands of factories discharge into the rivers. The Bangladesh Government is planning to install over 12 large Sewage Treatment Plants (STPs) over the next 20 years. To assess the efficacy of these, a water quality model has been applied to the Dhaka River System. Results show that the proposed plan has beneficial effects in the short term for the most densely populated areas of Dhaka, along the Turag and Buriganga Rivers, and in the medium term in other parts of the city (Tongi Khal). However, in several reaches dissolved oxygen levels will remain low or very low due to the lack of STP capacity, remaining misconnections of untreated sewage and large effluent loads. The proposed STPs, while certainly beneficial, will need to be upgraded in the future if the predicted rates of population growth are confirmed and industrial pollution is not significantly reduced alongside. Climate change is expected to have an impact on the Dhaka River System water quality, with increased monsoon flows and lower summer flows, but these changes will not greatly affect the extremes of water quality to any great extent due to the overwhelming impact of pollutant discharges into the system.

Comparison of typical nitrite oxidizing bacteria suppression strategies and the effect on nitrous oxide emissions in a biofilm reactor

In mainstream partial nitritation/anammox (PN/A), suppression of nitrite oxidizing bacteria (NOB) and mitigation of N2O emissions are two essential operational goals. The N2O emissions linked to three typical NOB suppression strategies were tested in a covered rotating biological contactor (RBC) biofilm system at 21 °C: (i) low dissolved oxygen (DO) concentrations, and treatments with (ii) free ammonia (FA), and (iii) free nitrous acids (FNA). Low emerged DO levels effectively minimized NOB activity and decreased N2O emissions, but NOB adaptation appeared after 200 days of operation. Further NOB suppression was successfully achieved by periodic (3 h per week) treatments with FA (29.3 ± 2.6 mg NH3-N L−1) or FNA (3.1 ± 0.3 mg HNO2-N L−1). FA treatment, however, promoted N2O emissions, while FNA did not affect these. Hence, biofilm PN/A should be operated at relatively low DO levels with periodic FNA treatment to maximize nitrogen removal efficiency while avoiding high greenhouse gas emissions.

Impact of Dissolved Oxygen on the Performance and Microbial Dynamics in Side-Stream Activated Sludge Hydrolysis Process

Dissolved oxygen (DO) plays an important role in the performance of biological wastewater treatment systems. This study investigated the effect of the DO concentration on nutrient removal performance and microbial community structure in side-stream activated sludge hydrolysis (SSH) and conventional anaerobic/anoxic/aerobic (A2O) processes. The results showed that the change in DO had little effect on the removal performance of chemical oxygen demand (COD), and the removal efficiencies were about 90% for both reactors. Compared with the high DO level (4.1–6.9 mg/L), the A2O and SSH reactors had better nitrogen removal performance at low (0.5–2.2 mg/L) and moderate (2.2–3.9 mg/L) DO levels, with ammonia (NH4+-N) removal efficiencies of 88–89% and 89–91%, respectively, and total nitrogen (TN) removal efficiencies of 74–76% and 75–81%, respectively. Directly reducing the DO concentration from high to low reduced the phosphate removal efficiencies of the A2O and SSH reactors from 80.2% and 86.2% to 63.1% and 70.6%, respectively, while re-elevating the DO concentration to moderate levels significantly improved the phosphate removal efficiencies to 94.6% and 96.0%, respectively. Compared to the A2O reactor, the SSH reactor had more stable and better nutrient removal performance under different DO conditions, partly due to the additional carbon sources produced through the sludge fermentation in the side-stream reactor. The decrease in the DO concentration resulted in a decrease in the relative abundance of Acinetobacter but an increase in the relative abundance of Competibacter, potentially leading to the deterioration in phosphorus removal.

Local intensity of artisanal gold mining drives mercury accumulation in neotropical oxbow lake fishes

Driven by surges in global gold prices and additional socio-economic factors, artisanal small-scale gold mining (ASGM) in the Global South is increasing and driving emissions of significant quantities of mercury (Hg) into the air and freshwater. Hg can be toxic to animal and human populations and exacerbate the degradation of neotropical freshwater ecosystems. We examined drivers of Hg accumulation in fish that inhabit oxbow lakes of Peru's Madre de Dios, a region with high biodiversity value and increasing human populations that depend on ASGM. We hypothesized that fish Hg levels would be driven by local ASGM activities, by environmental Hg exposure, by water quality, and by fish trophic level. We sampled fish in 20 oxbow lakes spanning protected areas and areas subject to ASGM during the dry season. Consistent with previous findings, Hg levels were positively associated with ASGM activities, and were higher in larger, carnivorous fish and where water had lower dissolved oxygen levels. In addition, we found a negative relationship between fish mercury levels associated with ASGM and the occurrence of the piscivorous giant otter. The link between fine-scale quantification of spatial ASGM activity and Hg accumulation, as indicated by the result that in the lotic environment, localized effects of gold mining activities are stronger drivers (77 % model support) of Hg accumulation than environmental exposure (23 %) constitutes a novel contribution to a growing body of literature on Hg contamination. Our findings provide additional evidence of high Hg exposure risks to neotropical human and top carnivore populations subject to the impacts of ASGM, which depend on freshwater ecosystems undergoing gradual degradation. The documented spatial variation in Hg accumulation and increased Hg levels in carnivorous fish should serve as a warning to human communities in Madre de Dios to avoid the proximity of high-intensity gold mining areas and minimize local carnivorous fish consumption.

Alteration of antioxidant status, glucose metabolism, and hypoxia signal pathway in Eirocheir sinensis after acute hypoxic stress and reoxygenation

Dissolved oxygen (DO) is crucial for the survival of Chinese mitten crab (Eirocheir sinensis); low DO levels adversely affect the health of these crabs. In this study, we evaluated the underlying response mechanism of E. sinensis to acute hypoxic stress by analyzing antioxidant parameters, glycolytic indicators, and hypoxia signaling factors. The crabs were exposed to hypoxia for 0, 3, 6, 12, and 24 h and reoxygenated for 1, 3, 6, 12, and 24 h. The hepatopancreas, muscle, gill, and hemolymph were sampled at different exposure times to detect the biochemical parameters and gene expression. The results showed that the activity of catalase, antioxidants, and malondialdehyde in tissues significantly increased under acute hypoxia and gradually decreased during the reoxygenation phase. Under acute hypoxic stress, glycolysis indices, including hexokinase (HK), phosphofructokinase, pyruvate kinase (PK), pyruvic acid (PA), lactate dehydrogenase (LDH), lactic acid (LA), succinate dehydrogenase (SDH), glucose, and glycogen in the hepatopancreas, hemolymph, and gills increased to varying degrees but recovered to the control levels after reoxygenation. Gene expression data showed that hypoxia signaling pathway-related genes, including hypoxia-inducible factor-1α/β (HIF1α/β), prolyl hydroxylase (PHD), factor inhibiting hypoxia-inducible factor (FIH), and glycolysis-related factors (HK and PK) were upregulated, showing that the HIF signaling pathway was activated under hypoxic conditions. In conclusion, acute hypoxic exposure activated the antioxidant defense system, glycolysis, and HIF pathway to respond to adverse conditions. These data contribute to elucidating the defense and adaptive mechanisms of crustaceans to acute hypoxic stress and reoxygenation.

Temperature sensitivity of oxygen demand varies as a function of organic matter source

Dissolved oxygen (DO) impairment within coastal waters is widespread and rising temperatures may exacerbate low DO levels by enhancing organic matter (OM) degradation. Here, the temperature sensitivity of OM degradation was investigated as DO decay rates determined during standard five-day biochemical oxygen demand (BOD) measurements conducted under different incubation temperatures. Sampling was conducted in the Waccamaw River watershed, South Carolina, a blackwater river with extensive forested wetland that also receives drainage from stormwater detention ponds associated with coastal development, thus providing different sources of contrasting OM composition. Temperature sensitivities were measured as Q10 temperature coefficients, which define how DO decay rates change with 10 degrees of warming. The average Q10 value for the wetland sites (2.14 ± 0.41) was significantly greater (p < 0.05) than those measured in either the River (1.49 ± 0.36) or stormwater ponds (1.41 ± 0.21). Furthermore, using Intergovernmental Panel on Climate Change intermediate-to-very high temperature estimates for 2100 of +2.7 – 4.4°C, average predicted increases in DO decay rates for wetlands (~22-39%) are more than double the River (~11-18%) and stormwater pond rates (~9-16%). Our findings for inland, coastal waters agree with previous results for soils, suggesting that temperature sensitivities are variable across sites and increase with more complex, lower quality OM. Future modeling scenarios of DO utilization must therefore consider the influence of OM heterogeneity and the temperature sensitivity response of OM degradation across sources and region to better predict how climate change may impact oxygen impairment in aquatic ecosystems.

Effects of habitat usage on hypoxia avoidance behavior and exposure in reef-dependent marine coastal species

Reef habitat in coastal ecosystems is increasingly being augmented with artificial reefs (ARs) and is simultaneously experiencing increasing hypoxia due to eutrophication and climate change. Relatively little is known about the effects of hypoxia on organisms that use complex habitat arrangements and how the presence of highly preferred AR habitat can affect the exposure of organisms to low dissolved oxygen (DO). We performed two laboratory experiments that used video recording of behavioral movement to explore 1) habitat usage and staying duration of individuals continuously exposed to 3, 5, and 7 mg/L dissolved oxygen (DO) in a complex of multiple preferred and avoided habitat types, and 2) the impact of ARs on exposure to different DO concentrations under a series of two-way replicated choice experiments with or without AR placement on the low-oxygen side. Six common reef-dependent species found in the northeastern sea areas of China were used (i.e., rockfish Sebastes schlegelii and Hexagrammos otakii, filefish Thamnaconus modestus, flatfish Pseudopleuronectes yokohamae, sea cucumber Stichopus japonicus, and crab Charybdis japonica). Results showed that lower DO levels decreased the usage of preferred habitats of the sea cucumber and the habitat-generalist filefish but increased the habitat affinity to preferred habitat types for the two habitat-specific rockfishes. Low DO had no effect on the crab’s habitat usage. In the choice experiment, all three fish species avoided 1 mg/L, and the rockfish S. schlegelii continued to avoid the lower DO when given choices involving pairs of 3, 5, and 7 mg/L, while H. otakii and the flatfish showed less avoidance. The availability of ARs affected exposure to low DO for the habitat-preferring rockfishes but was not significant for the flatfish. This study provides information for assessing the ecological effects and potential for adaptation through behavioral movement for key reef-dependent species under the increasing overlap of ARs and hypoxia anticipated in the future.

Characterization and Control of Oxygen Uptake in the Blanketing and Purging of Tanks with Inert Gases in the Winery

This work presents the study of the effectiveness of different inert gases applied during racking to prevent oxygen uptake by wine. Inert gases were used for the purging of empty tanks and hoses before the start of each racking, as well as for blanketing in the full racked tank. After analyzing these operations with the different inert gases, the required volumes of each gas were optimized. The CO2:Ar (20:80) mixture proved to be the most effective for the complete purging of the empty tank, while CO2 was the most cost-effective gas. Purging the empty tank with 25% vessel volume gas was sufficient to achieve useful inerting with all the gases studied, as well as to maintain low levels of dissolved oxygen (DO) in the wine filling the tank. Applying 0.5 of vessel volume of Ar, CO2:Ar (20:80), and CO2 gases during blanketing allowed the headspace oxygen (HSO) of the racked tank to be protected throughout. During the racking of a white wine in a commercial winery, Ar showed the highest efficiency, compared to N2, for both the inerting of empty hoses and destination tank and for maintaining low levels of DO and HSO in the tank.

Monitoring of Harmful Algal Bloom (HAB) of Noctiluca scintillans (Macartney) along the Gulf of Mannar, India using in-situ and satellite observations and its impact on wild and maricultured finfishes

In the Gulf of Mannar, Noctiluca scintillans blooms have been observed three times in September 2019, September and October 2020, and October 2021. It was determined and measured how the bloom period affects ichthyo-diversity. Noctiluca cell density varied slightly from year to year, ranging from1.8433 × 103 cells/L to 1.3824 x 106cells/L. In surface and sea bottom waters, high ammonia levels and low dissolved oxygen levels were noted. During the bloom period a significant increase in chlorophyll concentration was found. The amount of chlorophyll in GOM was extremely high, according to remote sensing photos made using MODIS-Aqua 4 km data. Acute hypoxia caused the death of wild fish near coral reefs and also in fish reared in sea cages. The decay of the bloom resulted in significant ammonia production, a dramatic drop in the amount of dissolved oxygen in the water, and ultimately stress, shock, and mass mortality of fishes.

Kajian Eksperimen Pengaruh Variasi Perubahan Sudut Kincir terhadap Kinerja Paddle Wheel Aerator

The main problem discussed in this study is the effort to improve the quality of shrimp pond water, especially the low dissolved oxygen levels by modifying the angle of the aerator wheel. The results showed that dissolved oxygen (DO) levels were very important in shrimp pond culture and that the paddle wheel aerator was a useful tool in intensive aquaculture systems because it could produce DO as needed. The study used a model designed using Solidworks software and tested at a scale of 1:10 with 3 variations of angles (15°, 35°, and 55°) at each wheel angle. The test results show that the angle variation affects the rotational speed and DO production, with the highest rotational speed and DO production achieved at an angle variation of 55°. However, the best parameters for the aerator were found at a variation of the wheel angle of 35° and a rotational speed of 300 rpm, because it produced the highest dissolved oxygen with relatively low power.

Effect of Anise Essential Oil Supplementation on Growth Performance of Nile Tilapia Reared at Low Dissolved Oxygen Level

Medicinal herbs are the most utilized and validated feed additives in the aquaculture industry. This study investigated the dietary effects of anise (Pimpinella anisum L.) in Nile Tilapia (Oreochromis niloticus). Three sets of diets were prepared by spraying Anise essential oil on a commercial basal diet (30% crude protein) at the rate of 0 (control), 1, and 2 mL/kg diet. The experimental groups were assigned a 3 × 2 factorial design (3 level of anise oil; 0, 1, 2 ml) × 2 levels of dissolved oxygen (DO) concentration. The experiment was assembled as a control no anise (high DO), 1 ml + (high DO), 2 ml + (high DO), Control 0 ml (low DO), 1 ml anise (low DO), and 2 ml anise (low DO). Fish were fed the diets for 60 days consecutively at 3% body weight. The feed intake was recorded daily by subtracting the remaining feed in the containers from the total amount of feed before feeding. The results showed a marked enhancement in the growth performance and reduced feed conversion ratio in fish-fed anise compared to the control group. The carcass composition showed that crude protein was meaningfully by 2.5 and 3.5 g anise per kg diet. In conclusion, incorporating anise into the diet of Nile Tilapia is suggested to enhance performances and well-being.

Uvidi u dinamiku pH, varijabilnost rastvorenog kiseonika i efikasnost uklanjanja jona u biološkom sistemu sa plutajućim ostrvima

This paper aims to analyse the dynamic responses within FTW constructed on the riverbank, focusing on pH, dissolved oxygen (DO), and the dynamics of calcium and magnesium concentrations. While some research has been carried out on Ca and Mg behavior in constructed wetlands no papers specifically addressed the removal mechanisms of these ions in FTWs have been found. Results showed that both polluted and treated water exhibited characteristics consistent with a mildly alkaline environment. Extremely low DO levels in cells with floating islands were increased after water passing through cell with algae. Ca removal efficiency in cells with floating island cells ranged from 2% to 6%, while the cell with algae achieved 23% to 49% efficiency. Modest Mg removal (1-6%) could indicate potential challenges in Mg removal processes within the FTWs. The analysis of plant responses to polluted water exposure reveals species-specific variations in Ca and Mg concentrations in shoots and roots. Ca concentration in algae tissue increased over time contrasting the marked decrease of Mg content. The study also revealed a gradual decrease of Ca and Mg concentration in stone wool corresponding to exposure duration. This research contributes to a better understanding of the complex dynamics of water treatment in FTWs, emphasizing the need for continued investigation into ion removal mechanisms, plant responses to increased Ca and Mg concentrations, and the role of algae in these biological systems.