Critical Oxygen Level Research Articles

Reduced seagrass resilience due to environmental and anthropogenic effects may lead to future die-off events in Florida Bay

Coastal systems often depend on foundation species such as seagrasses that are supported by self-facilitation. Seagrass meadows, however, are threatened worldwide due to climate change and local human impact, disrupting self-facilitation leading to system instability. Florida Bay is a large seagrass dominated coastal ecosystem that suffered from multiple seagrass mortality events over the last half century driven by hypoxia, high water temperatures, hypersalinity, and high biological oxygen demand. These conditions reduce the amount of photosynthetically-derived oxygen in the plant causing sulphide intrusion into meristematic tissues. Using a bay-wide sampling design and long-term monitoring trends of seagrass condition, we investigated the current state of the meadows, sediment characteristics (e.g., organic matter, sulphide, nutrients) and discuss how climate stressors interact with plant and sediment oxygen dynamics. Our survey revealed that at sites where seagrass had been previously denuded by die-off, the dominant seagrass Thalassia testudinum had not recovered, while the pioneering seagrass Halodule wrightii recolonized the impacted areas. Organic matter and sulphide levels were higher at the impacted sites, apparently a persistent characteristic of the formerly dense T. testudinum meadows in central and western Florida Bay. These sediment conditions promote sulphide intrusion of T. testudinum belowground tissue under anoxic conditions. Plant oxidation initially buffers sulphide intrusion, but disruption of this oxidation mechanism due to changing environmental conditions results in widespread mortality and seagrass community collapse. Climate change cannot be fully mitigated by local management, however, attempts can be made to control critical salinity and oxygen levels by increasing freshwater input, reducing hypersalinity and aiming to keep the internal seagrass oxidation feedback intact. Our study shows that the Florida Bay seagrass ecosystem is still recovering four years post die-off and continues to be susceptible to future climate change and system degradation.

Altering developmental oxygen exposure influences thermoregulation and flight performance of Manduca sexta.

Endothermic, flying insects are capable of some of the highest recorded metabolic rates. This high aerobic demand is made possible by the insect's tracheal system, which supplies the flight muscles with oxygen. Many studies focus on metabolic responses to acute changes in oxygen to test the limits of the insect flight metabolic system, with some flying insects exhibiting oxygen limitation in flight metabolism. These acute studies do not account for possible changes induced by developmental phenotypic plasticity in response to chronic changes in oxygen levels. The endothermic moth Manduca sexta is a model organism that is easy to raise and exhibits a high thorax temperature during flight (∼40°C). In this study, we examined the effects of developmental oxygen exposure during the larval, pupal and adult stages on the adult moth's aerobic performance. We measured flight critical oxygen partial pressure (Pcrit-), thorax temperature and thermoregulating metabolic rate to understand the extent of developmental plasticity as well as effects of developmental oxygen levels on endothermic capacity. We found that developing in hypoxia (10% oxygen) decreased thermoregulating thorax temperature when compared with moths raised in normoxia or hyperoxia (30% oxygen), when moths were warming up in atmospheres with 21-30% oxygen. In addition, moths raised in hypoxia had lower critical oxygen levels when flying. These results suggest that chronic developmental exposure to hypoxia affects the adult metabolic phenotype and potentially has implications for thermoregulatory and flight behavior.

Coping with environmental degradation: Physiological and morphological adjustments of wild mangrove fish to decades of aquaculture-induced nutrient enrichment

The impact of eutrophication on wild fish individuals is rarely reported. We compared physiological and morphological traits of Siganus lineatus chronically exposed to aquaculture-induced eutrophication in the wild with individuals living at a control site. Eutrophication at the impacted site was confirmed by elevated organic matter (up to 150 % higher), phytoplankton (up to 7 times higher), and reduced oxygen (up to 60 % lower). Physiological and morphological traits of S. lineatus differed significantly between the two sites. Fish from the impacted site exhibited elevated hypoxia tolerance, increased gill surface area, shorter oxygen diffusion distances, and altered blood oxygen-carrying capacity. Elevated blood lactate and scope for anaerobic ATP production were observed, suggesting enhanced survival below critical oxygen levels. A significant 8.5 % increase in metabolic costs and altered allometric scaling, related to environmental degradation, were recorded. Our study underscores eutrophication's profound impact at the organism-level and the importance to mitigate it.

Spiny dogfish, Squalus suckleyi, shows a good tolerance for hypoxia but need long recovery times.

Pacific spiny dogfish, Squalus suckleyi, move to shallow coastal waters during critical reproductive life stages and are thus at risk of encountering hypoxic events which occur more frequently in these areas. For effective conservation management, we need to fully understand the consequences of hypoxia on marine key species such as elasmobranchs. Because of their benthic life style, we hypothesized that S. suckleyi are hypoxia tolerant and able to efficiently regulate oxygen consumption, and that anaerobic metabolism is supported by a broad range of metabolites including ketones, fatty acids and amino acids. Therefore, we studied oxygen consumption rates, ventilation frequency and amplitude, blood gasses, acid-base regulation, and changes in plasma and tissue metabolites during progressive hypoxia. Our results show that critical oxygen levels (P crit) where oxyregulation is lost were indeed low (18.1% air saturation or 28.5Torr at 13°C). However, many dogfish behaved as oxyconformers rather than oxyregulators. Arterial blood PO2 levels mostly decreased linearly with decreasing environmental PO2. Blood gases and acid-base status were dependent on open versus closed respirometry but in both set-ups ventilation frequency increased. Hypoxia below Pcrit resulted in an up-regulation of anaerobic glycolysis, as evidenced by increased lactate levels in all tissues except brain. Elasmobranchs typically rely on ketone bodies as oxidative substrates, and decreased concentrations of acetoacetate and β-hydroxybutyrate were observed in white muscle of hypoxic and/or recovering fish. Furthermore, reductions in isoleucine, glutamate, glutamine and other amino acids were observed. After 6hours of normoxic recovery, changes persisted and only lactate returned to normal in most tissues. This emphasizes the importance of using suitable bioindicators adjusted to preferred metabolic pathways of the target species in conservation physiology. We conclude that Pacific spiny dogfish can tolerate severe transient hypoxic events, but recovery is slow and negative impacts can be expected when hypoxia persists.

Potential effects of shoaling of oxygen minimum zone on the population of Acartia (Acanthacartia) tonsa in the Humboldt Current Upwelling System (23°S)

Expansion and shoaling of the Oxygen Minimum Zone (OMZ) in coastal upwelling systems due to climate change can have dire consequences on the ecosystem structure and productivity. The OMZ restricts the habitat range of most zooplankton, and species with low tolerance to hypoxia may suffer physiological stress and mortality as a result. During 2013 and 2014, the copepod Acartia tonsa collected off northern Chile was used to evaluate how hypoxia may affect its survival and vital rates. Exposure of gravid females to severe hypoxia (∼0.2 mL L−1 dissolved oxygen) resulted in total mortality. Hypoxia at ∼0.5 mL L−1 decreased female survival to ∼20% and egg production to nil. Hypoxia at ∼0.8 mL L−1 decreased survival to ∼50% but no change in egg production rate compared to the normoxia treatment. Egg hatching success was ∼68% and naupliar development time was ∼36% lower in hypoxia than normoxia. The critical and lethal oxygen levels for the species were estimated to be 1.78 and 0.73 mL L−1, respectively. Based on modeled historical data, the 1.5 mL L−1 isopleth has been moving upward at a rate of 1.3–2.0 m per year in northern Chile, barring interruptions during El Niño events. The long-term, gradual shoaling of the OMZ is expected to have significant impacts on the zooplankton community and productivity in the region.

Determining Oxygen Consumption of Indonesian Mahseer (Tor soro) Fingerlings at Different Size and Stocking Density

Understanding oxygen consumption in fish is one of the essential factors in the survival performance of cultured fish. As this information is established, the appropriate size and optimum stocking density of cultured fish reared in an aquaculture system can be determined for successful larval rearing of mahseer in a hatchery. This study aimed to obtain information on the oxygen consumption rate and critical oxygen level of Indonesian mahseer fingerlings at different sizes and stocking densities. This study was conducted in the Laboratory of Fish Reproduction and Genetics, which belongs to the Research Institute for Freshwater Aquaculture and Fisheries Extension, Bogor. A factorial design with two factors (size and stocking density) and three replications were employed to run the experiments. Oxygen consumption rate was measured using a closed respirometer system (volume: 1.4 L) Parameters observed during the study are oxygen consumption rate and critical oxygen level. The results showed that the highest oxygen consumption rate was found at the size of 6-8 cm at 9.52 mg O2/g/minute with a stocking density of 7 fish/1.4 L. Oxygen consumption rate of mahseer was increased with the increase of size and stocking density. In this experiment, the critical oxygen level of mahseer fingerlings was observed at 1.44 mg/L. The obtained critical oxygen consumption could be used as a reference to determine the amount of dissolved oxygen that could support the survival rate of mahseer. In rearing practice, it would be important information used for designing early warning and mitigating culture systems to avoid deterioration of dissolved oxygen levels in the water. Therefore, this study can be recommended for improvement mahseer rearing practice for better hatchery production with providing an appropriate oxygenation system for fingerling growth.

Fisheries management and tipping points: Seeking optimal management of Eastern Baltic cod under conditions of uncertainty about the future productivity regime

AbstractHistorical patterns of the Eastern Baltic cod stock recruitment show a shift from a regime with high reproductive potential before the early 1980s to a regime with low reproductive potential since then. This shift can be attributed to increasingly unfavorable environmental conditions for cod reproduction at that time: critical salinity and oxygen levels, needed for successful egg and larval development, deteriorated. Yet, significant inflows of salt‐ and oxygen‐rich water from the North Sea or improved eutrophication management might trigger a shift back to a more productive regime. Coupling a statistical recruitment model to a state‐of‐the‐art, age‐structured bio‐economic model of the Eastern Baltic cod fishery, we study how optimal management depends on the uncertainty about the future productivity regime. We extend the predominantly theoretical literature on optimal management of a natural resource with a potential regime shift by analyzing an empirical model of age‐structured population dynamics and by allowing for the possibility of a back‐shift from a “bad” into a “good” regime. We find that with a higher probability of a shift back to the more productive regime the optimal management of the fishery becomes more conservative in the short run. We conclude that these benefits for the fishery warrant strong action reducing eutrophication to increase the probability of a regime shift back to high reproductive potential of the Eastern Baltic cod fishery.

Use of complex physiological traits as ecotoxicological biomarkers in tropical freshwater fishes.

We review the use of complex physiological traits, of tolerance and performance, as biomarkers of the toxicological effects of contaminants in subtropical and tropical freshwater fishes. Such traits are growing in relevance due to climate change, as exposure to contaminants may influence the capacity of fishes to tolerate and perform in an increasingly stressful environment. We review the evidence that the critical oxygen level, a measure of hypoxia tolerance, provides a valuable biomarker of impacts of diverse classes of contaminants. When coupled with measures of cardiorespiratory variables, it can provide insight into mechanisms of toxicity. The critical thermal maximum, a simple measure of tolerance of acute warming, also provides a valuable biomarker despite a lack of understanding of its mechanistic basis. Its relative ease of application renders it useful in the rapid evaluation of multiple species, and in understanding how the severity of contaminant impacts depends upon prevailing environmental temperature. The critical swimming speed is a measure of exercise performance that is widely used as a biomarker in temperate species but very few studies have been performed on subtropical or tropical fishes. Overall, the review serves to highlight a critical lack of knowledge for subtropical and tropical freshwater fishes. There is a real need to expand the knowledge base and to use physiological biomarkers in support of decision making to manage tropical freshwater fish populations and their habitats, which sustain rich biodiversity but are under relentless anthropogenic pressure.

Aerobic and anaerobic movement energetics of hybrid and pure parental abalone.

The underlying mechanisms controlling growth heterosis in marine invertebrates remain poorly understood. We used pure blacklip (Haliotis rubra) and greenlip (Haliotis laevigata) abalone, as well as their hybrid, to test whether differences in movement and/or aerobic versus anaerobic energy use are linked to a purported increased growth rate in hybrids. Abalone were acclimated to control (16°C) and typical summer temperatures (23°C), each with oxygen treatments of 100% air saturation (O2sat) or 70% O2sat. The experiment then consisted of two phases. During the first phase (chronic exposure), movement and oxygen consumption rates (ṀO2) of abalone were measured during a 2day observation period at stable acclimation conditions. Additionaly, lactate dehydrogenase (LDH) and tauropine dehydrogenase (TDH) activities were measured. During phase two (acute exposure), O2sat was raised to 100% for abalone acclimated to 70% O2sat followed by an acute decrease in oxygen to anoxia for all acclimation groups during which movement and ṀO2 were determined again. During the chronic exposure, hybrids and H. laevigata moved shorter distances than H. rubra. Resting ṀO2, LDH and TDH activities, however, were similar between abalone types but were increased at 23°C compared to 16°C. During the acute exposure, the initial increase to 100% O2sat for individuals acclimated to 70% O2sat resulted in increased movement compared to individuals acclimated to 100% O2sat for hybrids and H. rubra when compared within type of abalone. Similarly, ṀO2 during spontaneous activity of all three types of abalone previously subjected to 70% O2sat increased above those at 100% O2sat. When oxygen levels had dropped below the critical oxygen level (Pcrit), movement in hybrids and H. laevigata increased up to 6.5-fold compared to movement above Pcrit. Differences in movement and energy use between hybrids and pure species were not marked enough to support the hypothesis that the purportedly higher growth in hybrids is due to an energetic advantage over pure species.

Pengaruh Padat Tebar terhadap Konsumsi Oksigen dan Respons Stres Ikan Cupang Alam (Betta imbellis)

<strong>Effect of Stocking Density on Oxygen Consumption and Stress Response in Crescent Betta (<em>Betta imbellis</em>)</strong>. Stocking density is one of the determinant parameters for fish growth optimization in aquaculture systems due to its relationship with fish metabolism. Information about the impact of different stocking densities on crescent betta (<em>Betta imbellis</em>) metabolism was not available yet. This study was aimed to analyze the effect of stocking density on oxygen consumption, critical oxygen level, and stress responses in crescent betta.The study was carried out under three different stocking density treatments: 5, 10, and 15 fish/L with three replications using 2.74 ± 0.23 cm total length and 0.22 ± 0.05 g body weight tested fishes.The parameters observed were oxygen consumption, ventilation rate, blood glucose level, cortisol, and critical oxygen level. The result showed that the highest oxygen consumption was found at 5 fish/L stocking density treatment (3.01 ± 0.28 mg O<sub>2</sub>/g/h), which was significantly different from 10 fish/L (1.01 ± 0.21 mg O<sub>2</sub>/g/h) and 15 fish/L (0.92 ± 0.08 mg O<sub>2</sub>/g/h) stocking density treatments. Oxygen consumptions under hypoxic condition was not significantly different compared to normoxic condition.The ventilation rate tends to increase significantly along with the increasing of stocking densities. Critical oxygen levels were not significantly different among the treatments,with the value of 3.31 ± 0.65 mg/L, 3.14 ± 0.29 mg/L, and 2.83 ± 0.19 mg/L for stocking density of 5, 10, and 15 fish/L, respectively. The blood glucose level at 15 fish/L stocking density was significantly higher than others, whereas the cortisol levels was not significantly different among the treatments. The results of this study provided information that the increasing stocking density of cressent betta will decrease their metabolism activity and increase ventilation rate. However, the increase of ventilation rate was negatively correlated with oxygen consumption per breath at higher stocking densities due to decrease in fish activity; and higher stocking densities will decrease oxygen consumption. Based on the results, it can be concluded that the ideal stocking density for crescent betta is 5 fish/L. The increasing of stocking density will decrease oxygen consumption rates and increase the stress level of crescent betta.

A case of the unanticipated difficult airway where bougie was used as a conduit over I gel as a rescue airway for one-lung ventilation under direct vision of fiberoptic bronchoscopy

The basic foremost step for any surgery done under general anesthesia is to place an endotracheal tube (ETT) into the trachea. Placement of a definitive airway is vital to maintain a critical level of oxygen in the end organ during apnea time. There are multiple ways revealed in the literature to place ETT into the trachea. Sometimes, placement can be achieved speedily at the critical time with the experience of anesthesiologist and availability of different airway adjutants. Here, we describe a case of ETT intubation using bougie as a conduit over I gel under direct vision of fiberoptic bronchoscopy in a thymic enhancing mass.

The effect of hypoxia on hearing function

Background/aimThis study was conducted to determine the critical partial oxygen pressure (pO2) value that would impair hearing function by evaluating the effects of hypoxia on hearing function in subjects diagnosed with chronic obstructive pulmonary disease (CPOD).Materials and methodsThe study included 25 male and 5 female patients referred to our clinic who were diagnosed with COPD, according to spirometry and PaO2 values, and who did not show pathology upon autoscopic examination. The control group consisted of 14 female and 16 male patients who had no lung disease and were in the same age range as the COPD group.ResultsA statistically significant difference was found between the two groups for distortion-product otoacoustic emission (DPOAE) (P < 0.001). The COPD group was divided into two groups according to pO2 levels (pO2 ≤ 70 and pO2 > 70) in order to find a critical pO2 level which might cause significant change at a certain audiological extent.ConclusionHypoxia causes long-term decline in hearing thresholds, deterioration of DPOAE results, and prolongation of I–V interpeak latency in auditory brainstem response. However, the critical oxygen level that disrupts hearing function could not be determined.

Sublethal exposure to copper supresses the ability to acclimate to hypoxia in a model fish species

Hypoxia is one of the major threats to biodiversity in aquatic systems. The association of hypoxia with nutrient-rich effluent input into aquatic systems results in scenarios where hypoxic waters could be contaminated with a wide range of chemicals, including metals. Despite this, little is known about the ability of fish to respond to hypoxia when exposures occur in the presence of environmental toxicants. We address this knowledge gap by investigating the effects of exposures to different levels of oxygen in the presence or absence of copper using the three-spined sticklebacks (Gasterosteus aculeatus) model. Fish were exposed to different air saturations (AS; 100%, 75% and 50%) in combination with copper (20 μg/L) over a 4 day period. The critical oxygen level (Pcrit), an indicator of acute hypoxia tolerance, was 54.64 ± 2.51% AS under control conditions, and 36.21 ± 2.14% when fish were chronically exposed to hypoxia (50% AS) for 4 days, revealing the ability of fish to acclimate to low oxygen conditions. Importantly, the additional exposure to copper (20 μg/L) prevented this improvement in Pcrit, impairing hypoxia acclimation. In addition, an increase in ventilation rate was observed for combined copper and hypoxia exposure, compared to the single stressors or the controls. Interestingly, in the groups exposed to copper, a large increase in variation in the measured Pcrit was observed between individuals, both under normoxic and hypoxic conditions. This variation, if observed in wild populations, may lead to selection for a tolerant phenotype and alterations in the gene pool of the populations, with consequences for their sustainability. Our findings provide strong evidence that copper reduces the capacity of fish to respond to hypoxia by preventing acclimation and will inform predictions of the consequences of global increases of hypoxia in water systems affected by other pollutants worldwide.

Konsumsi Oksigen Ikan Uceng Nemacheilus fasciatus (Valenciennes, 1846) pada Kondisi Padat Tebar yang Berbeda

&lt;strong&gt;Oxygen Consumption of Barred Loach Nemacheilus fasciatus (Valenciennes, 1846) under Different Stocking Densities&lt;/strong&gt;. In aquaculture system, fish growth is affected by stocking densities. One way to predict the effect of stocking density on growth is to determine fish metabolic rate through oxygen consumption measurements. In Barred loach Nemacheilus fasciatus (Valenciennes, 1846), the information was scarce on oxygen consumption. This study was to analyze the effect of stocking density on oxygen consumption in Barred loach conducted at Research Institute for Freshwater Aquaculture and Fisheries Extension, Bogor in May 2018. Barred loach (total length: 5.79 ± 0.47 cm, weight: 1.32 ± 0.34 g) was observed its oxygen consumption on three different stocking densities (5, 10, and 15 fish/L) by using closed respirometers (volume: 1.4 L) with three replications of each treatment. Measurement of oxygen consumption was carried out under normoxia and hypoxia conditions. In addition, fish behavior and ventilation rate were also observed and recorded according to treatment. The results showed that the highest oxygen consumption of barred loach was found in the stocking density of 5 fish/L (1250.6 ± 128.4 mg O2/kg/h) which was significantly different from the stocking density of 10 fish/L (626.9 ± 46.7 mg O2/kg/h) and 15 fish/L (596.9 ± 48.9 mg O2/kg/h). Meanwhile, oxygen consumption of barred loach under hypoxic conditions decreased significantly compared to normoxic conditions, which was marked by a decrease in their swimming activities. Although the ventilation rate in hypoxic conditions has decreased, the value was not significantly different from those of normoxia condition. Results of this study provide information that an increase in stocking density and hypoxic conditions in barred loach caused a decrease in oxygen consumption rates. In addition, this study showed that the critical oxygen level for barred loach was around 3.1 mg/L

Long-term effects of ocean acidification upon energetics and oxygen transport in the European sea bass (Dicentrarchus labrax, Linnaeus)

The accumulation of CO2 in the atmosphere and resulting ocean acidification represent a threat to marine ecosystems. While acid–base regulatory capacity is well developed in marine fish, allowing compensation of extra-cellular pH during short-term hypercapnia, the possible energetic costs of such regulation during long-term exposure remain to be established. In this study, juvenile European sea bass (Dicentrarchus labrax) were exposed from 2 days post-hatching to three different ocean acidification scenarios: control (present condition, $$ P_{{{\text{CO}}_{2} }} $$ = 520 µatm, pH 7.9), moderate acidification ( $$ P_{{{\text{CO}}_{2} }} $$ = 950 µatm, pH 7.7), and high acidification ( $$ P_{{{\text{CO}}_{2} }} $$ = 1490 µatm, pH 7.5). After 1.5 years of exposure, fish aerobic metabolic capacities, as well as elements of their oxygen extraction and transport chain, were measured. Compared to control, $$ P_{{{\text{CO}}_{2} }} $$ treatments did not affect fish standard metabolic rate (SMR). However, the most severe acidification condition was associated with a significantly elevated maximum metabolic rate (MMR).This was supported by heavier gill system and higher blood haemoglobin concentration. A reduction of maximum cardiac frequency (fHmax) during incremental warming of anaesthetized fish was also observed in both acidification scenarios. On the other hand, the critical oxygen level (O2crit), the minimum oxygen level required to sustain SMR, did not differ among groups. The increased MMR, associated with maintained SMR, suggests that acid–base compensatory processes, although not increasing maintenance costs, may affect components of bass homeostasis, resulting in new internal physico-chemical conditions. The possibility that these alterations influence metabolic pathways and physiological functions involved in fish aptitude to maximally transport oxygen is discussed.

Hypoxia during incubation does not affect aerobic performance or haematology of Atlantic salmon (Salmo salar) when re-exposed in later life.

Hypoxia in aquatic ecosystems is becoming increasingly prevalent, potentially reducing fish performance and survival by limiting the oxygen available for aerobic activities. Hypoxia is a challenge for conserving and managing fish populations and demands a better understanding of the short- and long-term impacts of hypoxic environments on fish performance. Fish acclimate to hypoxia via a variety of short- and long-term physiological modifications in an attempt to maintain aerobic performance. In particular, hypoxia exposure during early development may result in enduring cardio-respiratory modifications that affect future hypoxia acclimation capacity, yet this possibility remains poorly investigated. We incubated Atlantic salmon (Salmo salar) in normoxia (~100% dissolved oxygen [DO, as percent air saturation]), moderate hypoxia (~63% DO) or cyclical hypoxia (100–25% DO daily) from fertilization until 113 days post-fertilization prior to rearing all groups in normoxia for a further 8 months. At ~11 months of age, subsets of each group were acclimated to hypoxia (50% DO) for up to 44 days prior to haematology, aerobic metabolic rate and hypoxia tolerance measurements. Hypoxia exposure during incubation (fertilization to 113 days post-fertilization) did not affect the haematology, aerobic performance or hypoxia tolerance of juvenile salmon in later life. Juveniles acclimated to hypoxia increased maximum aerobic metabolic rate and aerobic scope by ~23 and ~52%, respectively, when measured at 50% DO but not at 100% DO. Hypoxia-incubated juveniles also increased haematocrit and haemoglobin concentration but did not affect acute hypoxia tolerance (critical oxygen level and DO at LOE). Thus, while Atlantic salmon possess a considerable capacity to physiologically acclimate to hypoxia by improving aerobic performance in low oxygen conditions, we found no evidence that this capacity is influenced by early-life hypoxia exposure.

Effects of Hypoxia on Oxygen Consumption of Tilapia Fingerlings (Oreochromis niloticus)

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 &lt;em&gt;Oreochromis niloticus&lt;/em&gt; (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 O&lt;sub&gt;2&lt;/sub&gt;/kg/h) was lower than normoxia (35.67 ± 4.19 mg O&lt;sub&gt;2&lt;/sub&gt;/kg/h) (P&amp;lt;0.01). Continuous hypoxic conditions could negatively affect fish movements, which could ultimately lead to mortality when dissolved oxygen levels are very low. Meanwhile, the results on determination of critical oxygen levels for tilapia showed a dissolved oxygen range of 1.9 ± 0.5 mg/L.

Growth of Spiny Lobster Panulirus homarus Fed with Moist Diet

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&amp;lt;0.01). Continuous hypoxic conditions could negatively affect fish movements, which could ultimately lead to mortality when dissolved oxygen levels are very low. Meanwhile, the results on determination of critical oxygen levels for tilapia showed a dissolved oxygen range of 1.9 ± 0.5 mg/L

A rainbow trout Oncorhynchus mykiss strain with higher aerobic scope in normoxia also has superior tolerance of hypoxia.

This study compared parr from three strains of rainbow trout Oncorhynchus mykiss to examine intraspecific variation in metabolic traits, hypoxia tolerance and upper thermal tolerance in this species. At the strain level, variation in absolute aerobic scope (AAS), critical oxygen level (O2crit ), incipient lethal oxygen saturation (ILOS) and critical thermal maximum (CTmax ) generally exhibited consistent differences among the strains, suggesting the possibility of functional associations among these traits. This possibility was further supported at the individual level by a positive correlation between ILOS and O2crit and a negative correlation between O2crit and AAS. These results indicate that intraspecific differences in hypoxia tolerance among strains of O. mykiss may be primarily determined by differences in the ability to maintain oxygen uptake in hypoxia and that variation in aerobic scope in normoxia probably plays a role in determining the ability of these fish to sustain metabolism aerobically as water oxygen saturation is reduced.

Ecophysiological limits to aerobic metabolism in hypoxia determine epibenthic distributions and energy sequestration in the northeast Pacific ocean

AbstractExpansion of oxygen deficient waters (hypoxia) in the northeast Pacific Ocean (NEP) will have marked impacts on marine life. The response of the resident communities will be a function of their ecophysiological constraints in low oxygen, although this remains untested in the NEP due to a lack of integrative studies. Here, we combine in situ surveys and lab‐based respirometry experiments were conducted on three indicator species (spot prawnPandalus platyceros, slender soleLyopsetta exilis, squat lobsterMunida quadrispina) of seasonally hypoxic systems in the NEP to test if metabolic constraints determine distributions and energy sequestration in a hypoxic setting. These experiments were integrated with a global review of critical oxygen levels (; lower threshold of aerobic metabolism) for crustaceans to determine if‐based hypoxia thresholds are different among ocean basins. Our results show that species‐specific differences inand standard metabolic rates (1) determine the lowest environmental oxygen ([O2]env) at which in situ populations occur, (2) result in disproportionate shifts in distributions among co‐occurring species during summer hypoxia expansion events, and (3) characterize shifts in megafaunal community respiration rates due to marked spatio‐temporal variability in [O2]env. Our results show that‐based hypoxia thresholds are significantly lower in the East Pacific Ocean relative to other major ocean basins, which suggests that the physiological response of local fauna to deoxygenation can be determined by the natural variability and oxygen exposure in a region. In order to establish realistic predictions on the biological consequences of marine deoxygenation, we suggest integrating metabolism‐based traits to calculate hypoxia thresholds for marine ecosystems.