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Gomphonema alavariense sp. nov. is a new freshwater diatom described in Portugal from phytobenthos samples in an urban pond located in Aveiro (Portugal). This new diatom is illustrated and discussed based on different samples collected in July–August 2017 from Santo António Park pond in the city centre. This taxon was compared with other Gomphonema taxa and the morphological features are documented through light and scanning electron micrographs. Gomphonema alavariense sp. nov. is characterized by showing solitary cells, rhombic-lanceolate to lanceolate valves with rounded apices, a narrow, linear axial area, and slightly asymmetrical central area. This taxon may be confused with G. affine var. rhombicum in terms of length, striae density and outline. Gomphonema alavariense sp. nov. was present in freshwater with low dissolved oxygen concentrations, high conductivity, neutral to slightly alkaline pH and high nitrate concentrations.

The golden mussel (Limnoperna fortunei) has caused worldwide problems for the eco-environment and man-made structures. There have been many control strategies proposed, which have various strengths and weaknesses. To help selection of the effective control strategies that consider the biological traits of L. fortunei and the actual situation of biofouling, we studied the ecological amplitudes that indicate the tolerance of the species to environmental conditions and propose appropriate strategies based on their ecological amplitudes. We set five levels for the environmental factors water temperature, dissolved oxygen concentration, pH and ammonium ion concentration and four levels for light intensity. The survival ratio and attachment ratio of golden mussels under the different environmental conditions were measured and the nonlinear regression models were used to simulate the ecological amplitudes of golden mussel. The results show that their ecological amplitudes are wide-ranging with respect to water temperature (13–29 °C), dissolved oxygen (> 1.5 mg/L), pH (4.1–8.7), ammonium ions concentration (lower 65 mg/L) and light intensity (0–55,000 l x) and the mussels show obvious negative phototaxis. Therefore, adjustment of the environment with high water temperatures, low dissolved oxygen, high pH values or strong and continuous light illumination is suggested as a potentially effective control strategy of golden mussel biofouling.

Anthropogenic environmental degradation has led to an increase in the frequency and prevalence of aquatic hypoxia (low dissolved oxygen concentration, DO), which may affect habitat quality for water-breathing fishes. The weakly electric black ghost knifefish, Apteronotus albifrons, is typically found in well-oxygenated freshwater habitats in South America. Using a shuttle-box design, we exposed juvenile A. albifrons to a stepwise decline in DO from normoxia (> 95% air saturation) to extreme hypoxia (10% air saturation) in one compartment and chronic normoxia in the other. On average, A. albifrons actively avoided the hypoxic compartment below 22% air saturation. Hypoxia avoidance was correlated with upregulated swimming activity. Following avoidance, fish regularly ventured back briefly into deep hypoxia. Hypoxia did not affect the frequency of their electric organ discharges. Our results show that A. albifrons is able to sense hypoxia at non-lethal levels and uses active avoidance to mitigate its adverse effects.

International audience; Hypoxia and mercury contamination often co-occur in tropical freshwater ecosystems, but the interactive effects of these two stressors on fish populations are poorly known. The effects of mercury (Hg) on recorded changes in the detailed form of the electrocardiogram (ECG) during exposure to progressive hypoxia were investigated in two Neotropical freshwater fish species, matrinxã, Brycon amazonicus and traíra, Hoplias malabaricus. Matrinxã were exposed to a sublethal concentration of 0.1 mg L−1 of HgCl2 in water for 96 h. Traíra were exposed to dietary doses of Hg by being fed over a period of 30 days with juvenile matrinxãs previously exposed to HgCl2, resulting in a dose of 0.45 mg of total Hg per fish, each 96 h. Both species showed a bradycardia in progressive hypoxia. Hg exposure impaired cardiac electrical excitability, leading to first-degree atrioventricular block, plus profound extension of the ventricular action potential (AP) plateau. Moreover, there was the development of cardiac arrhythmias and anomalies such as occasional absence of QRS complexes, extra systoles, negative Q-, R- and S-waves (QRS complex), and T wave inversion, especially in hypoxia below O2 partial pressures (PO2) of 5.3 kPa. Sub-chronic dietary Hg exposure induced intense bradycardia in normoxia in traira, plus lengthening of ventricular AP duration coupled with prolonged QRS intervals. This indicates slower ventricular AP conduction during ventricular depolarization. Overall, the data indicate that both acute waterborne and sub-chronic dietary exposure (trophic level transfer), at sublethal concentrations of mercury, cause damage in electrical stability and rhythm of the heartbeat, leading to myocardial dysfunction, which is further intensified during hypoxia. These changes could lead to impaired cardiac output, with consequences for swimming ability, foraging capacity, and hence growth and/or reproductive performance.

Controlling dissolved oxygen (DO) at low level can save energy for wastewater treatment plants (WWTPs), but it is easy to induce filamentous sludge bulking. Through establishing the kinetic equation of sludge settleability, ammonia nitrogen (NH4+-N) load and organic load (food-to-microbe ratio, F/M), the mechanism of the competitive relationship between filamentous and floccular bacteria under low DO was analyzed. The results showed when DO, NH4+-N load and F/M were in the range of 0.15–0.35 mg/L, 0.035–0.15 d−1 and 0.12–0.42 d−1, respectively, the mass transfer limitation of organic matter was the main factor determining the dominant growth of filamentous bacteria. When DO, NH4+-N load and F/M were in the range of 0.35–0.65 mg/L, 0.035–0.065 d−1 and 0.12–0.22 d−1, respectively, the mass transfer limitation of NH4+-N was the main factor determining the dominant growth of filamentous bacteria. When DO was low, no matter how NH4+-N load and F/M changed, the growth of filamentous bacteria was promoted. When DO and F/M were in the range of 0.35–0.65 mg/L and 0.22–0.42 d−1, respectively, no matter how NH4+-N load and F/M changed, the growth of filamentous bacteria was inhibited. Therefore, in actual operation, ensuring relatively low DO and high F/M was beneficial for the sludge settleability improvement.

We incubated tomonts of Cryptocaryon irritans in a hypoxic seawater environment (1.4–1.7 mg/L O2) (low dissolved oxygen; DO) and examined their development using a acetocarmine whole-mount staining method we developed for nuclear staining. They showed little development and stayed in the dormant phase in the hypoxic environment. When transferred into the hypoxic environment after incubation in an oxic environment (air-saturated, 8.7–8.9 mg/L O2) for 1–4 days, their development stopped in 1 day. However, when dormant tomonts generated in the hypoxic environment were transferred to the oxic environment, they resumed development and released theronts. These results indicate that tomonts can become dormant when exposed to a hypoxic environment, but can resume development when exposed to an oxic environment at any developmental stage. When exposed to the oxic environment, tomonts recovered from 1-month dormancy and released as many theronts as control tomonts constantly incubated in the oxic environment. The infectivity of theronts from the recovered tomonts was similar to the control tomonts. Thermoclines prevent oxygen-rich surface seawater from reaching the bottom of water column and create a hypoxic sea floor environment in summer; these thermoclines are broken down in autumn or after typhoons. The long-term viability of dormant tomonts in hypoxic environments may be a key factor in the autumn outbreaks of cryptocaryoniasis in floating net cages in temperate waters.

The predatory cladoceran Bythotrephes longimanus (spiny water flea) has been invading lakes and damaging food webs across the central part of North America since the early 1980s. To understand its niche and that of the taxonomically related and native predatory cladoceran Leptodora kindtii, we investigated species survival after 12 h exposures to low dissolved oxygen (DO) concentrations in the laboratory. Bythotrephes longimanus (n = 690) exhibited a hypoxia tolerance limit (LC50) of 1.65 mg·L−1DO (95% confidence interval: 1.59, 1.72 mg·L−1) and was significantly less tolerant of hypoxia than L. kindtii (n = 380), which exhibited an LC50of 0.58 mg·L−1DO (0.51, 0.65 mg·L−1). These lab-based physiological results are consistent with landscape-scale observations that B. longimanus successfully invades primarily mesotrophic and oligotrophic lakes, while L. kindtii inhabits a wider range of lakes that includes eutrophic ones. Climate change throughout the 21st century may increase the occurrence and severity of hypoxia in the hypolimnia of lakes and may provide a growing barrier to B. longimanus invasion.

Pre-spawning mortality (PSM) has been occasionally observed in association with high densities of adult Pacific salmon ( Oncorhynchus spp.), but because large escapements are rare, the phenomenon remains poorly understood. A large spawning escapement (∼12 times the 54 year median, and 3X the previous maximum) to a small stream in Alaska provided a unique opportunity to explore the factors that contribute to density-driven spawning ground mortality. After comparing patterns of mortality in 2014 with over 20 years of prior abundance and environmental data, we identified low dissolved oxygen (DO) as likely contributing to PSM. We then utilized a fish habitat-DO model to explore the roles of density-dependent and -independent factors in reducing DO. Stream flow and spawning density were identified as primary drivers of oxygen availability. Despite suboptimal oxygen levels the salmon did not die abruptly. Rather, on average they lived as long as in previous years (mean = 9.99 d), but many (55%) failed to complete spawning prior to death. Our results suggest that this mortality was ultimately a density-dependent process, exacerbated by low-flow conditions. Given projected effects of climate change on river flows and temperatures, similar events may occur more frequently in parts of the range of salmon where abundances remain high.

Low-oxygen tolerance is important for aquaculture species, because exposure to hypoxia can result in heavy mortalities. This study evaluated the effects of strain, body weight, and gender on low-oxygen tolerance in channel catfish (Ictalurus punctatus) exposed to a lethal concentration of dissolved oxygen (0.1 mg/L). The variation in low-oxygen tolerance, assessed as the time to loss of equilibrium, of channel catfish from six strains (103KS, Kansas, KMix, Marion, Marion S, and Thompson) was examined. Catfish (15–179 g) showed a large variation in resistant time to hypoxia, ranging from 8 to 104 min, and both strain and body weight contributed significantly to this variation (P

Hypoxia (low dissolved oxygen [DO]) and CO2-induced acidification are important aquatic stressors that are exacerbated by anthropogenic nutrient inputs and are expected to increase in severity with increasing atmospheric CO2 and higher global temperatures. Understanding how species respond to changes in DO and pH is critical to predicting how climate change will affect estuarine ecosystems, including the extreme shallow margins of these systems, where factors such as respiration, photosynthesis, and tides create daily fluctuations of DO and pH, and strong correlations between the 2 stressors. To determine how acidification affects the sensitivity to hypoxia of 2 im portant forage fishes, the silversides Menidia menidia and M. beryllina, we recorded opercula ventilation rates, aquatic surface respiration (ASR, where fish breathe in the oxygenated surface layer during hypoxic events), and mortality as we lowered either DO or both DO and pH simultaneously. Fish subjected to low DO and low pH in the laboratory performed ASR and died at higher DO concentrations than fish subjected only to hypoxia. Additionally, fish beat their opercula slower, which may have contributed to the differences in ASR and mortality that we saw. These results indicate acidification can increase mortality under hypoxia not only directly but also indirectly by increasing vulnerability to predation during increased use of ASR.

Application of the modern microbial techniques changed the paradigm about the microorganisms performing nitrification. Numerous investigations recognized representatives of the genus Nitrospira as a key and predominant nitrite-oxidizing bacteria in biological nutrient removal systems, especially under low dissolved oxygen and substrate conditions. The recent discovery of Nitrospira capable of performing complete ammonia oxidation (comammox) raised a fundamental question about the actual role of Nitrospira in both nitrification steps. This review summarizes the current knowledge about morphological, physiological and genetic characteristics of the canonical and comammox Nitrospira. Potential implications of comammox for the functional aspects of nitrogen removal have been highlighted. The complex meta-analysis of literature data was applied to identify specific individual variables and their combined interactions on the Nitrospira abundance. In addition to dissolved oxygen and influent nitrogen concentrations, temperature and pH may play an important role in enhancing or suppressing the Nitrospira activity.

Low dissolved oxygen (hypoxia) can severely limit fish performance, especially aerobically expensive behaviours including swimming and acquisition of sensory information. Fishes can reduce oxygen requirements by altering these behaviours under hypoxia, but the underlying mechanisms can be difficult to quantify. We used a weakly electric fish as a model system to explore potential effects of hypoxia on swim performance and sensory information acquisition, which enabled us to non-invasively record electric signalling activity used for active acquisition of sensory information during swimming. To quantify potential effects of hypoxia, we measured critical swim speed (Ucrit) and concurrent electric signalling activity under high- and low-dissolved oxygen concentrations in a hypoxia-tolerant African mormyrid fish, Marcusenius victoriae. Fish were maintained under normoxia for 6 months prior to experimental treatments, and then acclimated for 8 weeks to normoxia or hypoxia and tested under both conditions (acute: 4 h exposure). Acute hypoxia exposure resulted in a significant reduction in both Ucrit and electric signalling activity in fish not acclimated to hypoxia. However, individuals acclimated to chronic hypoxia were characterized by a higher Ucrit under both hypoxia and normoxia than fish acclimated to normoxia. Following a 6 month re-introduction to normoxia, hypoxia-acclimated individuals still showed increased performance under acute hypoxic test conditions, but not under normoxia. Our results highlight the detrimental effects of hypoxia on aerobic swim performance and sensory information acquisition, and the ability of fish to heighten aerobic performance through acclimation processes that can still influence performance even months after initial exposure.

Published PCR primers targeting the ammonia monooxygenase gene (amoA) were applied to samples from activated sludge systems operated with low dissolved oxygen (DO) to quantify total and clade-levelNitrospirathat perform complete ammonium oxidation (comammox); however, we found these existing primers resulted in significant artifact-associated non-target amplification. This not only overestimated comammoxamoAcopies but also resulted in numerous false positive detections in the environmental samples tested, as confirmed by gel electrophoresis. Therefore, to more accurately quantify known comammox, we designed specific and sensitive primers targeting three candidate species:Candidatus(Ca.) Nitrospira nitrosa,Ca.N. inopinata, andCa.N. nitrificans. The primers were tested withamoAtemplates of these candidate species, and used to quantify comammox at the species level in low DO activated sludge systems. We found that comammox related toCa.N. nitrosa were present and abundant in the majority of samples from low DO bioreactors and were not detected in samples from a high DO system. In addition, the greatest abundance ofCa.N. nitrosa was found in bioreactors operated with a long solids retention time.Ca.N. inopinata andCa.N. nitrificans were only detected sporadically in these samples, indicating a minor role of these comammox in nitrification under low DO conditions.Abstract art

The aquatic environment presents daily and/or seasonal variations in dissolved oxygen (DO) levels. Piava faces different DO levels in the water due to its distributional characteristics. The goal of this study was to describe the effects of low DO levels on plasma ion, biochemical and oxidative variables in piava juveniles. Fish were exposed to different DO levels, including 1.0, 2.0, 3.0, 4.0 and 5.0 mg L-1 of DO for 96 h, after which blood and tissue samples (liver, kidney, gill and muscle) were collected. The decrease in DO levels decreased plasma Na+, Cl-, K+ and NH3 levels as well as protein and glycogen levels in the liver, kidney and muscle; increased Na+/K+-ATPase activity in the gills and kidney as well as glucose and ammonia levels in the liver, kidney and muscle; and increased lactate levels in the kidney and muscle. Thiobarbituric acid-reacting substances, catalase and non-protein thiol levels decreased in the tissues of piavas exposed to low DO levels. It is concluded that piava can apparently cope with hypoxic conditions; however, low DO levels are a stressor, and the tolerance of piava to hypoxia involves iono-regulatory, metabolic and oxidative adjustments.

Summer mortality (SM) in greenlip abalone ( Haliotis laevigata Donovan) heavily affects productivity of land-based abalone farms in Southern Australia. It has been associated with conditions of high water temperature (> 23 °C), low dissolved oxygen levels, and a range of other stressful factors in the culture water during summer months. This study aimed to alleviate mortality experienced by abalone at high water temperatures (26 °C), by dietary intervention using grape seed extract (GSE) and dried Ulva lactuca Linnaeus, two products which contain antioxidative and bioactive compounds. These products were formulated into a commercial abalone diet at levels of 5 and 30%. The diets were fed to 3-year-old greenlip abalone (26.8 g; 57.9 mm) at a water temperature of 22 or 26 °C for 38 days. No mortalities were observed at 22 °C. Compared to the unaltered commercial diet, both GSE and dried U. lactuca additive diets significantly increased the survival of abalone at the 26 °C water temperature ( P P U. lactuca to act as dietary additives to reduce mortality and improve productivity on abalone farms subjected to high summer water temperatures.

Because sturgeon populations are in critical decline, many species are artificially propagated in hatcheries with the goal of increasing wild stocks. Capture, transport, handling, confinement, and environmental fluctuations are just a few of the possible stressors Pallid Sturgeon Scaphirhynchus albus can be exposed to in conservation hatcheries. The objectives of the present study were to elucidate the effects of acute exposure to high ammonia concentrations, low dissolved oxygen (DO) concentrations, and crowding on stress responses in Pallid Sturgeon, quantified by changes in plasma cortisol and glucose. Exposure to un-ionized ammonia-nitrogen concentrations of 0.6 mg/L for 24 h resulted in no significant (P > 0.05) change in plasma cortisol concentrations, suggesting these fish do not perceive the buildup of toxins. Exposure to 2 mg/L DO over a 0.5-h period resulted in a significant (P 0.0...

Four groups of female channel catfish ( Ictalurus punctatus ) x male blue catfish ( I. furcatus ) hybrids were compared for tolerance of critically low dissolved oxygen, 0.6 ppm. Genotype–environment interactions ( P P

We monitored depths and temperatures used by large (>71-cm) versus small Northern Pike Esox lucius in three north-central Minnesota lakes with either acoustic telemetry or archival tags. Individual Northern Pike demonstrated flexibility in depths used within a season and between years. The fish had some tolerance for low levels of dissolved oxygen (

A number of reports describe the impact of hypoxic conditions on the manila clam Ruditapes philippinarum , but few deal with the after-effects of hypoxia on this clam species. Exposure experiments were carried out on the manila clam under conditions of low dissolved oxygen (DO, 0.5 mg/L). In the first exposure experiment (i.e., 3 days of hypoxia), a substantial change in mortality rate, glycogen content, and clearance rate was not observed in the period following the hypoxia. However, in the second exposure experiment (i.e., an additional 3 days of hypoxia following recovery from the first exposure), the mortality rate was significantly increased relative to that of the first exposure experiment, and glycogen content underwent a long-term decline. At the end of the experimental period, subsequent to the 2 exposures to hypoxia, the clearance rate had decreased until it was 77% of that of the normal manila clams unexposed to hypoxia. Moreover, the clearance rate was unable to recover following the second exposure. Thus, when the manila clams were repeatedly exposed to hypoxic conditions, the surviving individuals showed a residual disability, as reflected in the increased mortality and unrecovered clearance capacity. Afterward, the after-effects of hypoxia exposure on the clearance function of the manila clams in Omaehama beach, Japan, were assessed using the experimental results and the observed data. An examination of the effects of the residual disability showed a more extensive decrease in filtering capacity when a formula accounting for residual disability was used rather than a standard one. The clearance volume using our new formula was 75% of that of a standard formula. The formula equations that have been used up until now have only evaluated whether the manila clams die. However, the surviving individuals have a residual disability, and our formula indicates this effect would cause a further decline in the purification function of the beach.

Notropis photogenis (Silver Shiner) and Etheostoma zonale (Banded Darter) were collected from the Flint River in Madison County, AL, a northern tributary to the Tennessee River. Both species have been found in other northern tributaries to the Tennessee River in Alabama, but have not been widely reported from the Flint River. The Flint River is currently considered to be impaired water due to elevated turbidity, and has also been impaired in recent years from organic enrichment/low dissolved oxygen and pathogens in the form of fecal coliform.

Under natural conditions,animals often need to carry out digestion and locomotion simultaneously.The physiological design of their cardio-respiratory systems must accommodate these simultaneous demands either by according emphasis to one of them or by somehow sharing them.The outcomes of the competition between digestion and locomotion i.e.,metabolic modes,are ecologically important in fish species.In this study,we selected crucian carp(Carassius carassius),one of the most hypoxia tolerant fish as experimental model and aimed to investigate the effect of water dissolved oxygen level on digestion,locomotion and their interaction in juvenile crucian carp.To achieve this goal,we measured the critical swimming speed(Ucrit),pre-exercise oxygen consumption rate(MO2pre-exercise),active oxygen consumption rate(MO2active) and metabolic scope(MS) of both fasting and fed fish at 8,2 and 1 mg/L water dissolved oxygen level,under water temperature of(25.0±0.5) ℃.The MO2pre-exercise of fasting and fed fish(satiate meal size) were 212.1 vs 488.3,181.1 vs 418.2 and 106.4 vs 238.3 mg/kg.h,respectively,at 8,2 and 1 mg/L.The Ucrit of fasting and fed fish were 5.83 vs 6.15,5.17 vs 4.74 and 3.78 vs 3.08 BL/s,respectively,at 8,2 and 1 mg/L.Digestion had no effect on Ucrit at 8 mg/L,but it caused a significantly lower Ucrit in both 2 and 1 mg/L.The MO2active of fasting and fed fish were 689.9 vs 957.5,587.5 vs 687.1 and 434.7 vs 469.9 mg/kg.h while the MS of fasting and fed fish were 463.2 vs 469.2,406.4 vs 268.8 and 328.3 vs 231.6 mg/kg.h,respectively,at 8,2 and 1 mg/L.At 8 mg/L,the postprandial increase in resting MO2 was maintained at all levels of swimming speed till the highest swimming speed and fed fish showed a similar Ucrit and MS but a significantly higher MO2active,which indicated that crucian carp exhibit the additive metabolic mode in normoxia.It suggest that the juvenile crucian carp can handle both digestion and aerobic locomotion simultaneously in normoxia due to the higher respiratory capacity and relatively lower metabolic capacity of digestive and locomotive tissues.Since the respiratory capacity(as indicated by MO2active of fed fish) decrease more acutely than swimming capacity(as indicated by Ucrit and MO2active of fasting fish) with the decrease of dissolved oxygen level,the elevated MO2 due to digestion can be maintained under only lower swimming speed throughout the Ucrit test at both low dissolved oxygen level,but the fed fish end up having a profoundly lower Ucrit and MS and a similar MO2active compared with fasting fish,which indicate that crucian carp exhibit the digestion-priority metabolic mode in hypoxia due to the intensified oxygen demand competition between digestion and locomotion.The present study showed that the impairment of postprandial aerobic swimming performance increased with decreasing water dissolved oxygen level due to the unparalleled changes in the central cardio-respiratory,peripheral digestive and locomotory capacities of crucian carp.The different metabolic strategies of juvenile crucian carp at different water dissolved oxygen levels may relate to changes in oxygen demand and supply.

Silver perch Bairdiella chrysoura are an abundant and ecologically important species that are exposed to major hypoxic events throughout much of their range. Acute sensitivity tests (24 h) were conducted, and the lethal concentration of low dissolved oxygen (DO) determined for B. chrysoura (mean ± SE) 32.5 ± 4.0 mm standard length (SL) at 1.10 mg l �1 (95% CI, 0.43�1.52 mg l �1 ). The avoidance by B. chrysoura to low DO was tested based on size class (mm SL): ≤25, between 26�50, 51�75, and ≥76, with normal DO concentrations (control) throughout a par - titioned aquarium, and later, with an oxygen gradient from low DO ( 5 mg l �1 ). There was a significant difference between the expected and observed distribution for the 3 smaller size classes towards higher DO levels, while the largest size class showed no signif- icant difference in distribution and a G-test showed that oxygen choice levels were significantly different between size classes. The 3 largest size classes of B. chrysoura were tested in a swimming speed apparatus under 3 current speeds (0.17, 0.25, and 0.36 m s �1 ) with both high DO and low DO concentrations. A 3-way ANOVA showed that there was a significant increase in swimming capacity with increasing fish size, decreasing current speed, and increased DO, as well as a significant interaction between all 3 variables. This is one of the first studies to examine size-related responses to low DO in a sciaenid fish.

In Tolo Harbour, Hong Kong, where hypoxia occurs periodically, a large amount of benthic epifauna was found to be absent in the summer but become abundant again in the winter. This observation may indicate that some species are sensitive in detecting low dissolved oxygen (DO) levels and are able to escape from the harbour to more oxygenated, open waters when conditions deteriorate and return when DO levels are improved. Analysis of biological traits of these animals showed that 58% of the categories showed significant differences between the community structure in summer and winter. The significant biological traits of the few species, which remained in the harbour under the summer’s hypoxic conditions suggested adaptation rather than opportunism to the low DO levels. Our data also showed that trawling can increase DO at the bottom and may benefit the less sensitive species that remained in the habitat during the summer.

Oxygen is a vital parameter in aquaculture activities. The decrease of dissolved oxygen levels in aquaculture media should be highly observed, since very low dissolved oxygen conditions (hypoxia) could negatively affect to the growth and survival of fish. Therefore, research on the condition of hypoxia is very important to be studied. This study was conducted in January-February 2013 at the Laboratorium of Fish Reproductive Physiology, Pukyong National University, South Korea to measure oxygen consumption in tilapia Oreochromis niloticus (total length: 14.2 ± 1.4 cm, weight: 31.3 ± 2.0 g) under normal conditions (normoxia) and hypoxia. Measurement was conducted using respirometer (dimension: 20 × 17,5 × 10 cm; volume: 3,5 L) every 10 minutes during four hours of observation. Experiment was conducted with three replications. The results showed that oxygen consumption of tilapia fingerlings in hypoxia conditions (12.09 ± 3.20 mg O2/kg/h) was lower than normoxia (35.67 ± 4.19 mg O2/kg/h) (P

Egg masses of channel catfish Ictalurus punctatus are typically incubated in mesh baskets suspended in metal troughs with rotating paddles fitted between the baskets that move the water to agitate the eggs. This system is widely used, but stress caused by low dissolved oxygen resulting from poor water circulation through the egg masses at higher egg loading rates can cause reduced hatch. We designed and tested a vertical-lift incubator to improve hatch with higher egg loading rates. Angle-aluminum racks were placed inside standard hatchery troughs. Three baskets with hinged lids were placed in each rack and the egg masses were placed in the baskets. The racks in a pair of troughs were connected to overhead bars that oscillated at six cycles per minute, raising the rack in one while lowering the rack in the adjacent trough. Egg masses were incubated at a mean ± SE loading rate of 33.4 ± 4.7 lb per trough, which is nearly twice the recommended rate, with no supplemental oxygen. Survival from egg th...

The aim of this study was to assess the mean lethal concentration (LC50) of dissolved oxygen in high ammonia concentration and also the LC50 of ammonia under hypoxic conditions for juveniles of dourado, Salminus brasiliensis. In the first experiment, the non-ionized ammonia (NH3) concentrations were: 0.026, 0.447, 0.612, 0.909, and 1.334 mg/L, and the dissolved oxygen concentration was maintained at approximately 1.65 mg/L. In the second experiment, the dissolved oxygen concentrations were: 1.64, 1.99, 3.33, 5.10, and 7.77 mg/L, and the non-ionized ammonia concentration was kept at approximately 0.927 mg/L. The mean lethal concentrations of non-ionized ammonia varied from 0.584 to 0.577 mg/L, indicating that LC50 values were almost unaffected by exposure time. The estimated LC50 of dissolved oxygen varied from 4.02 to 5.02 mg/L, indicating a slight increase in the mean lethal concentrations as the exposure time increased. Results from this study indicate that interaction between these two parameters increases mortality and also suggest that dourado is susceptible to the combination of high ammonia with low dissolved oxygen concentrations.

In 1973, a project to evaluate the feasibility of culturing native anguillid eels as an export product was undertaken by the Philippine Bureau of Fisheries. Species identification, distribution and relative abundance of elvers, and culture feasibility were studied. Three species of anguillid eels were identified in streams throughout the north coastal region of Luzon Island: Anguilla marmorata, A. celebesensis, and A. bicolor pacifica. Elvers of all three species migrated simultaneously. Only A. bicolor pacifica appears suitable for commercial culture at present. Commercial quantities of elvers were found only in the Cagayan River. During 1973–74, 2.2 metric tons of elvers were collected from this river. In culture experiments, elvers grew well on a ration of ground fish with vitamin additives and showed a 6:1 feed conversion. A pelleted feed appeared desirable for fingerling and larger eels (>3g). Elvers succumbed to oxygen concentrations less than 2ppm; fingerling and larger eels were more tolerant of low dissolved oxygen. Mean water temperature of 25.3 C appeared suitable for year-round culture. Commercial culture operations were toured at the conclusion of the Bureau of Fisheries Project. Initial developments, problems and potentials were evaluated.

article The Northern Adriatic Sea experiences seasonal low dissolved oxygen (DO) events and mortality of benthic organisms.Theonsetandextentofsuchdisturbances,however,aredifficulttoforecastandstudyinthe field.We address this problem by deploying a device that artificially induces and documents small-scale anoxia on soft- bottom in 24 m depth. Behaviour changes and mortality sequences of the soft-bottom macroepi- and infauna over a 5.5-day deployment were documented. An intervening oxygen peak created two phases of declining oxygenvalues.Allinitiated behaviours were interrupted duringthereoxygenation andpredictably re-appeared in the second phase, demonstrating the direct relationship between oxygen levels and behaviour. Beginning hypoxia(≤2.0mll -1 DO)elicitedescapepatternssuchasincreasedhorizontalandverticallocomotion.Moderate hypoxia (≤1.0 ml l -1 DO) triggered species-specific sublethal effects such as arm-tipping in ophiuroids or extension from the sediment in sea anemones. At severe hypoxia (≤0.5 ml l -1

The Topeka shiner Notropis topeka is an endangered fish species, historically described as inhabiting cool, headwater prairie streams. However, Topeka shiners recently have been found in off-channel habitats with high temperatures and low concentrations of dissolved oxygen. In laboratory experiments to determine whether Topeka shiners can tolerate the conditions in these off-channel habitats for extended periods, we found that their optimum temperature for growth was approximately 27°C and their critical thermal maximum was 39°C at a 31°C acclimation temperature. Topeka shiners grew at dissolved oxygen concentrations as low as 2 mg/L, but at a considerably lower rate than at 4 mg/L and above. The concentration of dissolved oxygen that was lethal for 50% of the fish after 96 h at 26°C was 1.26 mg/L. Growth was reduced by Asian tapeworm infections. Overall, high temperatures and low dissolved oxygen are probably not limiting factors for Topeka shiner populations in most off-channel habitats.

Estuarine hypoxia (

Prochilodus nigricans , locally known as curimata, is an Amazonian commercial fish that endures adverse environmental conditions, in particular low dissolved oxygen, during its migration. Poorer environmental conditions are expected in the near future. Prochilodus nigricans overcomes current seasonal and diurnal changes in dissolved oxygen by adjusting erythrocytic levels of ATP and GTP, modulators of Hb-O 2 affinity. Will this fish species be endangered under more extreme environmental conditions as hypoxia and acidification tend to occur in a shorter period of time? As P. nigricans does not exhibit any apparent morphological alterations to exploit the air–water interface, it must rely on fast adjustments of blood properties. To investigate this aspect, basic hematology indices, pHe, pHi, plasma lactate, erythrocytic levels of ATP and GTP and functional properties of the hemolysate of P. nigricans were analyzed over a period of 6 h in hypoxia and subsequent recovery in normoxia. The levels of erythrocytic GTP were four times higher than ATP and were reduced to ¼ of the original level after 3 h under hypoxia. Erythrocytic levels of ATP were unaffected over the experimental period. All other analyzed blood parameters exhibited a time-course change in animals under hypoxia and returned to normoxic levels. Considering the hemolysate functional properties and the ability to regulate the above mentioned blood characteristics, P. nigricans is able to endure short-term changes in dissolved oxygen.

Water chemical analyses, porewater and whole sediment chemical analyses, and pore- water and whole sediment toxicity testing were performed as part of a combined effort between the US Fish and Wildlife Service and the US Geological Survey. These analyses were used to predict impaired stream sites that may impede a healthy natural riverine community. The analyses also revealed differences between sites that currently support and those that have ceased to support mus- sel populations. We estimated risk scores for the riverine community based on water and sediment characteristics. To identify and rank habitat in need of restoration, the risk estimation was derived by comparing collected data to water quality standards, sediment quality guidelines and toxicity test controls. High-risk scores often coincided with areas that no longer support historical freshwater mussel populations. Based on the data collected, factors thought to impede the existence of a natural riverine community included: sediment toxicity (porewater and whole sediment), sediment lead, sediment manganese, sediment ammonia, and low dissolved oxygen.

The objective of this study was to determine whether fry of golden shiners Notemigonus crysoleucas reared in ponds differed with respect to growth, survival, feed conversion, total yield, condition, and response to low dissolved oxygen when fed a practical diet of 36% protein from animal and plant sources (five ponds) versus a diet of only plant sources (six ponds). Newly hatched fry (1 mg) were stocked at 2.5 × 106/ha in 12 fertilized ponds (0.04 ha each). Fish were fed twice daily at a rate of 8.0–15.9 kg/ha for 12 weeks. Chlorophyll a was not different between diets, indicating that natural food production in ponds was similar between treatments. Between-treatment differences in average individual weight (0.56–0.59 g), relative weight (114.4– 115.6), Fulton's condition index (K = 0.88), total yield (40.8–45.6 kg), feed conversion (0.85– 0.95), and survival (75.9–79.2%) were not significant. Postharvest survival of fish exposed to low dissolved oxygen at 20°C in a laboratory test was not affect...

Vertebral deformities in red sea bream, Pagrus major, remain serious obstacles to the improvement of seedling quality for its aquaculture. However, the causalities of the deformities remain unclear and prevention methods have not yet been established. In this paper, oxygen deficiency during somitogenesis was demonstrated to cause centrum defects (formerly called fused vertebrae in many cases), which are the major vertebral deformity in cultured red sea bream. An induction experiment of centrum defects was conducted by placing fertilized red sea bream eggs under low dissolved oxygen conditions (10.3–16.6%). The low oxygen treatment was carried out for five different developmental stages of embryo: two-cell stage to blastula stage; gastrula stage; three to 10 somites stage; 11–17 somites stage and 18–24 somites stage. Oxygen deficiency during somitogenesis induced a high incidence of centrum defects. In contrast, it hardly induced centrum defects during the other stages. The dissolved oxygen concentration in the rearing water should be carefully regulated for fertilized eggs, especially during somitogenesis to reduce the incidence of vertebral deformities in the red sea bream.

The utility of splenic macrophage aggregates (MAs) as an indicator of fish exposure to degraded environments was evaluated in several species of estuarine fishes as part of the Environmental Protection Agency's Environmental Monitoring and Assessment Program–Estuaries (EMAP-E). Using image analysis, we measured the number and mean size of MAs per square millimeter on tissue sections of spleen from 983 fishes representing seven species from 266 stations scattered across coastal estuaries of the Gulf of Mexico. At 16 stations, at least one fish exhibited a high density of MAs (>40 MAs/mm2). Densities of MAs that exceeded 40/mm2 correlated with exposure to either hypoxic conditions or sediment contamination. Fisher's exact test showed that the observed frequencies of joint occurrence between high numbers of MAs and both high sediment contaminants and low dissolved oxygen were significantly greater than the expected background frequencies. For all 16 sites where MAs were greater than 40/mm2, sediment...

O experimento teve como objetivo avaliar a influência da suplementação de vitamina C na dieta sobre o desempenho de alevinos de piauçu (Leporinus obtusidens). Um primeiro ensaio (105 dias) testou o efeito da suplementação de níveis crescentes de L-ácido ascórbico (0, 50, 150, 250, 350, 450, 550, 650, 750 e 850 mg/kg) na dieta sobre ganho de peso e sobrevivência, num delineamento inteiramente ao acaso. Não houve diferenças significativas (P > 0,4054) entre os tratamentos, tanto para ganho de peso como sobrevivência. Num segundo ensaio avaliou-se a influência da vitamina C na resistência dos alevinos à hipoxia. Grupos de dez peixes aleatoriamente selecionados de cada tratamento do primeiro ensaio foram estocados em gaiolas, num delineamento em blocos ao acaso. A suplementação com vitamina C na dieta não afetou (P > 0,4032) a sobrevivência dos alevinos submetidos a hipoxia (oxigênio dissolvido abaixo de 1,0 mg/L) por até 14 horas. Contrariamente aos nossos resultados, a literatura mostra que a suplementação dietética com ácido ascórbico tem efeito benéfico, nos parâmetros avaliados, nas várias espécies de peixes. Assim, sugerimos que novos estudos sejam realizados no sentido de se definir o nível de suplementação de vitamina C em dietas para alevinos de piauçu.

This study examines the effects of harsh environmental conditions on life history trade-offs in parental care in a marine fish, the common goby, Pomatoschistus microps. We compared male parental care and hatching success over two sequential brood cycles in fish breeding in conditions of either low dissolved oxygen or normal levels of oxygen. Males compensated for a low oxygen environment by increasing the time they spent fanning water over their eggs, as well as their fanning tempo. They also increased the frequency of egg-directed activities and decreased nest-building activities. Males in the low oxygen treatment lost more weight than control fish during the first spawning, and were more likely to abandon care during the second spawning. Males that completed care under low oxygen conditions did not differ from control males in the hatching success of their offspring or the size of young at hatching, but hatching started on average 1 day later. Thus, greater parental allocations to offspring while breeding in a harsh environment led to reduced future allocations. Copyright 1999 The Association for the Study of Animal Behaviour.

Through use of a closed, circulating system, we examined the effects of low oxygen on the behavior and survival of juvenile Elliptio complanata, a common freshwater clam. Clams exposed to low oxygen exhibited increased stress behavior, extending their siphons, gaping, and surfacing more often than clams exposed to higher concentrations of oxygen. Stress levels rose with exposure time and led to increased mortality in a long-term study. Low oxygen in sediments may limit juvenile survival through direct mortality and indirectly through behaviors that can lead to increased mortality. Knowledge of the limitations may prove useful in clam reestablishment programs and for regulation of management practices near existing clam beds.

Individuals are commonly exposed to fluctuating levels of stressors, while most laboratory experiments focus on constant exposures. We develop and test a mathematical model for predicting the effects of low dissolved oxygen (hypoxia) on growth, reproduction, and survival using laboratory experiments on fish and shrimp. The exposure-effects model simulates the hourly reductions in growth and survival, and the reduction in reproduction (fecundity) at times of spawning, of an individual as it is exposed to constant or hourly fluctuating dissolved oxygen (DO) concentrations. The model was applied to seven experiments involving fish and shrimp that included constant and fluctuating DO exposures, with constant exposures used for parameter estimation and the model then used to simulate the growth, reproduction, and survival in the fluctuating treatments. Cumulative effects on growth, reproduction, and survival were predicted well by the model, but the model did not replay the observed episodic low survival days. Further investigation should involve the role of acclimation, possible inclusion of repair effects in reproduction and survival, and the sensitivity of model predictions to the shape of the immediate effects function. Additional testing of the model with other taxa, different patterns of fluctuating exposures, and different stressors is needed to determine the model's generality and robustness.

Limited filamentous bulking (LFB) was proposed to be a new method for saving energy and improving effluent quality. In order to validate the stability of LFB in enhanced biological phosphorus removal (EBPR) systems, the LFB was further achieved in a lab-scale EBPR. Nutrient removal performance and microbial community structure including dominant filaments and polyphosphate-accumulating organisms (PAOs) were investigated. Results showed that the enriched PAOs could alleviate the negative effect of low dissolved oxygen concentration on sludge settleability, making the LFB be more easily achieved and maintained in the EBPR for long-term operation. Sludge volume index was kept between 150–200 mL/g during the LFB period. Larger floc size (⩾400 μm) was commonly observed under the LFB state, which significantly enhanced the simultaneous nitrification and denitrification (SND) efficiency. An average SND efficiency of 36% was observed in the EBPR system when the LFB occurred.

Growth. feed consumption, and survival were evaluated for young red grouper Epinephelus morio reared in a recirculating-water system over 283 d. This fish-holding system was chosen because of site constraints and scarcity of seawater. Red grouper were size-graded into four experimental groups and fed chopped frozen clupeids. Water quality was monitored weekly. Daily growth rates of 0.48–0.69 g/fish were lower than those for other grouper species cultured in tanks or floating net cages. Survival ranged from 93.3 to 93.7% for three of the size-groups. Daily feed consumption rates progressively declined during the trial from 3.1–4.7% to 0.9–1.0% of body weight. Some pathological syndromes, such as exophthalmia and abdominal distension, appeared after day 283, resulting in high mortalities in all size-groups. Deaths were probably due to low dissolved oxygen (3.9–4.7 mg/L) during the last 39 d of the grow-out trial. Further studies are needed before the feasibility of red grouper culture can be adequa...

The addition of feed to fertilized fish ponds was evaluated by adding feed alone, feed plus fertilizer, or fertilizer alone to nine ponds stocked with Nile tilapia Oreochromis niloticus. Two experiments were conducted. The first had 500 fish per 250 m2 pond in 3 treatments: ad-libitum feeding; fertilizer only; or fertilizer and ad-libitum feeding. The second experiment had 5 treatments with 750 fish per pond ad-libitum feed only; fertilizer only; or 0.25, 0.50, and 0.75 satiation ration plus fertilizer. Ponds in Thailand were maintained for 155–162 d, during which chemical and physical properties were monitored. In experiment 1 tilapia growth was highest in feed only ponds, and lowest in fertilizer only ponds. Net yield did not differ significantly among treatments, due to variation in survival. In experiment 2, tilapia growth was lowest in fertilizer only ponds, intermediate in 0.25 ration ponds, and highest in 0.50, 0.75, and ad-libitum ponds. The latter treatments were not significantly different. Multiple regressions for each experiment indicated only 47–87% of the variance in growth was explained by feed and fertilizer input, while 52–89% of the variance in yield was explained by those factors. For both experiments combined, 90.3% of the variance in growth was explained by feed input, fertilizer input, alkalinity, and total inorganic nitrogen concentration. For yield, R2 was 0.888 and the regression included feed input, pH, and number of low dissolved oxygen events. Experiment 1 appeared to approach carrying capacity near the end, while no reduction in growth occurred in experiment 2 at higher fish density and biomass. Reductions in growth in experiment 1 were not correlated with declining water quality late in the grow out. Combinations of feed and fertilizer were most efficient in growing tilapia to large size (500 g) compared to complete feeding or fertilizing alone.

A substrate feeding strategy using an oxystat was first successfully applied to a fed-batch phenylalanine fermentation. The control method allowed the fermentation to be under low dissolved oxygen tension, which was favourable phenylalanine formation, and to be from substrate inhibition during the course of fed-batch operation. The final product concentration was 3 times higher than in a batch culture.

Larvae of sardine Sardinops sagax and anchovy Engraulis encrasicolus in the northern Benguela upwelling system were distributed predominantly in waters with dissolved oxygen concentrations >2.0 ml l(-1) and oxygen saturations >75%.

A pilot study of sewage treatment lagoons near Melbourne indicated that the best way to enhance nitrogen removal in such lagoons was to promote nitrification. Combined algal/bacterial biofilms grown on surfaces immersed in the lagoons showed potential for greatly increasing the extent of nitrification. A laboratory study was undertaken to determine the effect of pH, dissolved oxygen concentration, temperature and other factors on the nitrifying capabilities of such biofilms; effective nitrification was observed at temperatures down to 10°C, at pH's down to 5.5 and at dissolved oxygen levels down to 2.5 mg/L. Tanks containing biofilm-coated plates nitrified much more effectively than tanks containing only suspended microbial growths. At dissolved oxygen levels of 2-3 mg/L, up to 30% of the ammonia-nitrogen fed to tanks containing biofilm-coated plates was removed by denitrification. Photosynthetic activity in the biofilm greatly enhanced nitrification efficiencies at low dissolved oxygen levels.

Two groups of Nephelopsis obscura were maintained under identical conditions (20 °C, 100% dissolved oxygen, 12 h light: 12 h dark regime, ad libitum food) from post-hatchling size (10–11 mg) to sexual maturity (500–700 mg). One group (winter N. obscura) had overwintered in the field and degrown to 10–11 mg, while the other group (summer N. obscura) had hatched in the laboratory. The winter N. obscura at post-hatchling size had significantly lower accumulations of total lipid (3.9%), total protein (50.7%), free amino acids (1.6%), and glycogen (3.4%) than summer leeches, indicating that winter stresses (low water temperatures, low dissolved oxygen, restricted prey availability) had reduced energy stores and caused degrowth. The cryoprotective glycerol concentration, however, was significantly higher (1.9%) in winter leeches. At or just prior to sexual maturity, both winter and summer leeches showed decreases in total protein, glycogen, and total lipid which were attributed to the increased energetic demands of gametogenesis and maturation. The effects of, and compensation for, winter stresses were evident throughout the development of the winter leeches which exhibited enhanced energy allocation to storage compared with summer leeches.

The occurrence of hypoxia (< 2 mg 1-l) is being reported with increasing frequency In estuarine ecosystems, however the impacts of this environmental stress are often difficult to evaluate Since changes induced by episodes of hypoxia or anoxia may be impossible to distinguish from the natural variability of b~ological communities often it is only possible to infer effects based on measurements of low dissolved oxygen that colncide with events of catastrophic mortality In the present study, alteration In the operational schedule of a tide gate in the Back h v e r estuary (Savannah, Georgia USA) enabled an examination of the responses of 3 species of estuarine organisms to hypoxia survival was measured for caged amphipods Gammarus tigrlnus and bivalves Mul ln~a la tera l~s and ~Mercenar~a mercenana deployed near the tide gate during phases of its operation (reduced ebb flow) and nonoperation (normal tidal flow) Water quality parameters showed that while the tide gate was operated during periods of seasonally elevated water temperature bottom waters downstream of the gate became hypoxic The interruption of normal ebb flow was clearly linked to the onset of increased stratification and resultant d~ssolved oxygen depletion G tignnus was more sensitive to hypoxia than the bivalves, and laboratory tests suggested that mortality can result after as little as 3 h of exposure to oxygen saturation levels between 12 and 18 % The posslble ecological consequences of hypox~a In the Savannah k v e r estuary are discussed

Angler catches of white crappie Pomoxis annularis and the abundance of adult white crappies in cove rotenone samples decreased significantly in Chickamauga Reservoir from 1970 through 1989. Conversely, densities of larvae and young of year increased (nonsignificantly) during this period. In the 1970s, year-class strength was variable, but high young-of-year densities resulted in increased abundance and angler catch rates when the cohorts reached adult sizes. During the 1980s, reproductive success and survival through the first summer were adequate, but few white crappies reached harvestable size. Expansion of aquatic vegetation and resulting changes in fish and invertebrate community structures appeared to be the most important factors affecting survival of young white crappies in Chickamauga Reservoir. Also, low dissolved oxygen conditions associated with a 1985–1988 drought may have limited survival of age-1 and older white crappies. Prior to 1988, white crappies were the predominant Pomoxis sp...

The spionid poluchaete Streblospio benedicti (Webster) is common in surface sediments of estuarine intertidal and subtidal habitats. Because of their broad distribution, S. benedicti populations are often exposed to hypoxia or anoxia during summer in estuaries with periodic deoxygenation. The opportunistic behavior of S. benedicti after disturbance (e.g., hypoxia or anoxia) has been recognized; however, its tolerance of low dissolved O2 has not been studied. In the present study, tolerance and behavior to hypoxia, anoxia and hydrogen sulfide of adult S. benedicti were determined in laboratory experiments. Under severe hypoxia, adults survived for at least 2 wk without significant mortality at two experimental dissolved O2 concentrations (14.5 and 7% air saturation at 26°C). In anoxia, all worms died within 55 h. The behavior of S. benedicti was modified; feeding ceased and burrowing activities were reduced in hypoxia and anoxia. Most worms came out to the sediment surface at time of death. Survival of worms exposed to anoxia and moderate concentrations of hydrogen sulfide (< 66 μM) was not decreased in comparison to reference individuals in anoxia alone. Results from this study suggest that field populations of S. benedicti may survive intermittent periods of hypoxia, but that the intensity and duration of low dissolved O2 events may be critical to survivorship and local population persistance.