Air-breathing behavior and physiological responses to hypoxia and air exposure in the air-breathing loricariid fish, Pterygoplichthys anisitsi

Hypoxic water and episodic air exposure are potentially life-threatening conditions that fish in tropical regions can face during the dry season. This study investigated the air-breathing behavior, oxygen consumption, and respiratory responses of the air-breathing (AB) armored catfish Pterygoplichthys anisitsi. The hematological parameters and oxygen-binding characteristics of whole blood and stripped hemoglobin and the intermediate metabolism of selected tissue in normoxia, different hypoxic conditions, and after air exposure were also examined. In normoxia, this species exhibited high activity at night and AB behavior (2–5 AB h^?1). The exposure to acute severe hypoxia elicited the AB behavior (4 AB h^?1) during the day. Under progressive hypoxia without access to the water surface, the fish were oxyregulators with a critical O₂ tension, calculated as the inspired water O₂ pressure, as 47 ± 2 mmHg. At water O₂ tensions lower than 40 mmHg, the fish exhibited continuous apnea behavior. The blood exhibited high capacity for transporting O₂, having a cathodic hemoglobin component with a high Hb–O₂ affinity. Under severe hypoxia, the fish used anaerobic metabolism to maintain metabolic rate. Air exposure revealed physiological and biochemical traits similar to those observed under normoxic conditions.     

Physiological and morphological effects of severe hypoxia,hypoxia and hyperoxia in juvenile turbot (Scophthalmus maximus L.)

We studied the physiological status of juvenile turbot (Scophthalmus maximus L.) under severe hypoxia (1 and 2 mg/L dissolved oxygen, DO), hypoxia (3 and 5 mg/L DO), hyperoxia (11 and 14 mg/L DO) and normoxia (7 mg/L DO, control) conditions. The respiratory rates, haematology parameters, acid–base balance status and gill structure were analysed to find the effects of different DO concentration on turbot. Fish mortality was only observed under severe hypoxia conditions. Severe hypoxia caused an increase in respiratory rates and red blood cell counts, as well as an increase in haemoglobin and haematocrit levels in the fish. In fish exposed to hypoxia conditions, the respiratory rate increased overall as the DO concentration decreased. Lower pCO₂ and HCO₃^? levels led to a high blood pH, while the pO₂ remained stable. In hyperoxia groups, respiratory rate decreased as the DO concentration increased. The levels of pCO₂ and HCO₃^? significantly increased (P < 0.05), while the pO₂ level and blood pH did not change obviously. The gill structure was damaged after prolonged exposure to hyperoxia, but no obvious damage was found in hypoxia groups. The fish that survived the hypoxia or hyperoxia treatment were able to restore the structural integrity of the gills after 14 days' recovery. The results suggest that juvenile turbots can tolerate a wide range of DO concentrations. However, even mild hyperoxia condition (11 mg/L DO), which is widely used in fish culture, has adverse effects on juvenile turbot physiology.     

Effects of diet on spontaneous locomotor activity and oxygen consumption in Adriatic sturgeon (Acipenser naccarii)

Adriatic sturgeon (Acipenser naccarii) were maintained on a commercial diet enriched either in long chain polyunsaturated fatty acids of the 3 series (3 LCPUFA) or in saturated fatty acids (SFA). The effects of dietary fatty acid composition on spontaneous locomotor activity in normoxia and hypoxia (O₂ tension = 10.5 ± 0.8 kPa), and on oxygen consumption (M^O ₂) in normoxia, in hypoxia (O₂ tension = 6.6 ± 0.8 kPa) and during recovery were then investigated. The effects of adding supplementary vitamin E to the fat-enriched diets were also studied.Dietary fatty acid composition had effects on spontaneous locomotor activity and M^O ₂ in normoxia. Activity levels were higher in all sturgeon fed extra dietary fats (without vitamin E), when compared with control animals, but fish fed 3 LCPUFA had a significantly lower M^O ₂ than those fed SFA, with intermediate M^O ₂ in controls. In hypoxia, sturgeon 3 LCPUFA did not alter activity or M^O ₂ whereas those fed SFA reduced both and controls reduced M^O ₂. During recovery, both animals fed SFA and controls had a higher M^O ₂ than sturgeon fed 3 LCPUFA. The data indicate that fish fed 3 LCPUFA are more tolerant of hypoxia than controls or those fed SFA, as they did not reduce either activity or M^O ₂, and consumed less O₂ during recovery.Vitamin E supplements modified the effects elicited by dietary fats. All sturgeon fed vitamin E had low activity levels in normoxia and hypoxia. Sturgeon fed vitamin E with 3 LCPUFA had a higher M^O ₂ in normoxia than those fed 3 LCPUFA alone; reduced M^O ₂ in hypoxia, and during recovery increased M^O ₂ to a rate higher than that of animals fed 3 LCPUFA alone. In normoxia, sturgeon fed vitamin E with SFA had a similar M^O ₂ to those fed SFA alone but did not change M^O ₂ in hypoxia or during recovery. Thus, the effects of vitamin E were dependent on fat composition of the diet. Vitamin E with 3 LCPUFA removed the beneficial effects on M^O ₂ and responses to hypoxia obtained with 3 LCPUFA alone, but vitamin E with SFA allowed sturgeon to maintain aerobic metabolism in hypoxia, a more effective response than that observed in fish fed SFA alone.     

Effects of dietary fatty acid composition on metabolic rate and responses to hypoxia in the European eel (Anguilla anguilla)

European eels (Anguilla anguilla, L.) were fed on a commercial diet supplemented either with 15% by dry feed weight of menhaden oil (MO), an oil rich in highly unsaturated fatty acids of the n-3 series (n-3 HUFA), or with 15% by dry feed weight of coconut oil (CO), an oil composed primarily of saturated fatty acids (SFA). Following 90 days of feeding, the mean final masses of eels fed the two different oil supplements were similar, and higher than the mean final mass of a group fed the commercial diet alone. The diets created two distinct phenotypes of eels, distinguished by the fatty acid (FA) composition of their tissue lipids. Eels fed MO had significantly more total n-3 FA and n-3 HUFA in muscle and liver lipids than did eels fed CO, leading to higher n-3/n-6 and eicosapentaenoic acid/arachidonic acid ratios in the MO group. Measurements of O₂ uptake (M_O2) revealed that the MO group had a significantly lower routine metabolic rate (RMR) than the CO group. When exposed to progressive hypoxia, both groups regulated M_O2 at routine normoxic levels until critical water O₂ partial pressures that were statistically similar (9.62±1.08 kPa in MO versus 7.57±1.07 kPa in CO), beyond which they showed a reduction in M_O2 below RMR. The MO group exhibited a significantly lower M_O2 than the CO group throughout hypoxic exposure, but the percentage reductions in M_O2 below their relative RMR were equal in both groups. During recovery to normoxia, both groups exhibited an increase in M_O2 to rates significantly higher than their RMR. Throughout recovery, M_O2 was significantly lower in the MO group compared with the CO group, but the percentage increases in M_O2 relative to RMR were equal in both. During progressive hypoxia, neither group exhibited a marked ventilatory reflex response, both showed similar reductions in blood O₂ partial pressure and content, and similar increases in plasma lactate. The results indicate that, although the n-3 HUFA-enriched MO group had a significantly lower routine metabolic rate than the CO group, the difference in aerobic metabolism did not influence the European eel's homeostatic regulation of M_O2 in hypoxia.     

Effects of low dissolved oxygen on the digging behaviour and metabolism of the hard clam (Meretrix lusoria)

The dissolved oxygen (DO) concentration that induces the onset of anaerobic metabolism in hard clams was found to be 1.11 mg O₂ L^?1, at which time, the concentration of succinate in the body fluid was 4.4 μmol mL^?1. When the DO concentration was <1.11 mg O₂ L^?1, the burial depth was significantly reduced, and succinate significantly accumulated in the body fluid. After 24 h of anoxic exposure, succinate had accumulated in the gills and equal amounts of succinate and alanine had accumulated in the foot. This indicates that carbohydrates in the gills and amino acids in the foot contribute to anaerobic energy production. The accumulation rates of succinate and propionate in the body fluid were the highest compared with those in other tissues, while no accumulation of alanine in the body fluid was found. The recovery rates of succinate in the body fluid and alanine in the foot were the highest compared with those in other tissues. The results of this study suggest that the DO concentration in the bottom water of clam ponds should be maintained at ≥1.11 mg O₂ L^?1, and the anoxia‐tolerant ability of hard clams can be assessed by the contents of carbohydrates.     

Aerobic and anaerobic enzymatic activity of orange roughy (<Emphasis Type="Italic">Hoplostethus atlanticus</Emphasis>) and alfonsino (<Emphasis Type="Italic">Beryx splendens</Emphasis>) from the Juan Fernandez seamounts area

The aerobic and anaerobic enzymatic activity of two important commercial bathypelagic species living in the Juan Fernández seamounts was analyzed: alfonsino (Beryx splendens) and orange roughy (Hoplostethus atlanticus). These seamounts are influenced by the presence of an oxygen minimum zone (OMZ) located between 160 and 250 m depth. Both species have vertical segregation; alfonsino is able to stay in the OMZ, while orange roughy remains at greater depths. In this study, we compare the aerobic and anaerobic capacity of these species, measuring the activity of key metabolic enzymes in different body tissues (muscle, heart, brain and liver). Alfonsino has higher anaerobic potential in its white muscle due to greater lactate dehydrogenase (LDH) activity (190.2 μmol NADH min^?1 g ww^?1), which is related to its smaller body size, but it is also a feature shared with species that migrate through OMZs. This potential and the higher muscle citrate synthase and electron transport system activities indicate that alfonsino has greater swimming activity level than orange roughy. This species has also a high MDH/LDH ratio in its heart, brain and liver, revealing a potential capacity to conduct aerobic metabolism in these organs under prolonged periods of environmental low oxygen conditions, preventing lactic acid accumulation. With these metabolic characteristics, alfonsino may have increased swimming activity to migrate and also could stay for a period of time in the OMZ. The observed differences between alfonsino and orange roughy with respect to their aerobic and anaerobic enzymatic activity are consistent with their characteristic vertical distributions and feeding behaviors.     

Low stress response exhibited by juvenile yellowtail kingfish (Seriola lalandi Valenciennes) exposed to hypercapnic conditions associated with transportation

Transportation of yellowtail kingfish (Seriola lalandi Valenciennes) juveniles from hatchery to on‐growing operations in New Zealand exposes the fish to significantly elevated carbon dioxide (CO₂) concentrations. Experiments were undertaken to assess metabolic and haematological stress responses after a 5‐h period of hypercapnia, followed by recovery in normocapnia. Mortality was low (0.5%) and secondary stress indices (blood glucose, blood lactate, muscle pH and muscle lactate) remained largely unchanged during a simulated transportation and recovery, despite juveniles being exposed to CO₂ concentrations as high as 75 mg CO₂ L^?1 (38 mm Hg partial pressure). There was some haematological disturbance midway through simulated transports, where water was maintained at fixed CO₂ concentrations of 8 and 50 mg CO₂ L^?1 (4 and 26 mm Hg respectively). Persistent erythrocyte swelling continued during transport at 50 mg CO₂ L^?1, whereas at 8 mg CO₂ L^?1, haematological variables had returned to control levels. There was no mortality recorded for any of the treatments, and haematological variables were restored to pre‐manipulation levels after 31 h. The results indicated that juvenile yellowtail kingfish have a robust physiology and can cope with the stressors imposed by acute exposure to moderate to high levels of CO₂ associated with live transport.     

Blood oxygen tension and content in carp, Cyprinus carpio L., during hypoxia and methaemoglobinaemia

Carp respond to water hypoxia with an evaluation in the rate of gill ventilation. In order to characterize closer the adequate stimulus for the increase in respiratory drive specimens of carp, Cyprinus carpio L., were exposed simultaneously to moderate environmental hypoxia (P^wO²? 75mmHg, 10kPa) and elevated water nitrite concentration (089 ± 0-lmmol/l) for 24h. The differential effects of these treatments were utilized to distinguish between the responses to an immediate reduction in water and arterial Po_a (P,O²), and to the slowly developing reduction of arterial oxygen content (C^aO²) and functional oxygen saturation (S^aO²). After onset of hypoxia gill ventilation quickly increased, leading to a reduction in P_aCO₂. Slowly rising blood methaemoglobin levels resulted in a gradual decline in C^aO² and S^aO² over 24h, whereas P002 remained steady for the entire exposure period. This pattern of lowered P^aco² and P_aO₂, essentially constant for 24 h, together with the lack of any correlation with changes in C^aO², suggests PO₂ (P^a,O² and/or P^wo²) as the primary stimulus in the regulation of ventilation of carp.     

The effects of temperature on the physiological response to low oxygen in Atlantic sturgeon

Atlantic sturgeon (Acipenser oxyrhynchus), which are bottom dwelling and migratory fish, experience environmental hypoxia in their natural environment. Atlantic sturgeon, acclimated to either 5 or 15°C, were subjected to a 1 h severe (<10 mm Hg) hypoxia challenge in order to document their physiological responses. We measured hematological parameters, including O₂ transport (hemoglobin, hematocrit), ionic (chloride, osmolality), and metabolic (glucose, lactate) variables under normoxic conditions (~160 mm Hg), immediately following a 1 h exposure to hypoxic water, and following a further 2 h of recovery from this challenge in normoxic water. In a second experiment, we assessed the opercular beat frequency before, during, and after hypoxic exposure. Hemoglobin concentrations and hematocrit were significantly different between fish held at 5°C vs. 15°C and also significantly different between normoxia prior to hypoxia and following recovery. Plasma lactate concentrations increased following hypoxia at both temperatures, indicative of an increase in anaerobic metabolism. In contrast, a significant increase in plasma glucose concentrations in response to hypoxia only occurred at 5°C, suggesting different fuel demands under different temperatures. Changes in opercular beat frequency (OBF) were dependent on temperature. At 5°C, OBF increased upon exposure to hypoxia, but returned to pre-exposure levels within 35 min for the remainder of the experiment. During hypoxia at 15°C, OBF increased very briefly, but then rapidly (within 20 min) decreased to levels below control values. Following a return to normoxia, OBF quickly increased to control levels. Overall, these findings suggest that Atlantic sturgeons are relatively tolerant to short-term and severe hypoxic stress, and the strategies for hypoxia tolerance may be temperature dependent.     

Effects of growth hormone on plasma ionic regulation,respiration and extracellular acid-base status in trout (Oncorhynchus mykiss) transferred to seawater

The effects of trout recombinant growth hormone (rtGH) treatment (0.25 g g^–1 by intraperitoneal implant) on plasma ionic regulation, extracellular acid-base status and respiration were investigated in freshwater rainbow trout and during a 4-day period after direct transfer into seawater (35 g 1^–1).In freshwater, rtGH treatment resulted in a significant increase in gill (Na⁺, K⁺) ATPase activity and in standard metabolism (MO₂). The latter would mainly result from a higher rate of protein synthesis. Direct transfer from freshwater to seawater induced a decrease in arterial blood pH, far more pronounced in controls than in treated fish. This effect could be regarded in both groups mainly as a metabolic acidosis resulting from extracellular ion composition changes (i.e., an increase higher in chloride than in sodium, more marked in controls than in treated fish). As the rise in PaCO₂, in spite of an increase in ventilatory activity, is more significant in controls than in treated fish, it can be assumed that rtGH treatment lightened the decrease in the gas diffusing capacity of gills induced by transfer to seawater. The initial increase in MO₂ in both controls and treated fish could be the consequence of an increase in energetic cost of ventilation and osmoregulation. Then, in treated fish, the persistent high level of M may indicate a stimulation of intermediary metabolism by rtGH. In addition, the absence in treated fish of an increase in plasma lactate concentration, as observed in controls, would indicate that rtGH attenuated the decrease in O₂ affinity of haemoglobin foreseeable from the metabolic acidosis.This article is dedicated to Professor Claude Peyraud, whose recent death has deeply saddened us. We respectfully pay a tribute to his memory.     

Physiological responses of largemouth bass to acute temperature and oxygen stressors

Abstract Temperature and oxygen gradients exist in nearly every water body, but anthropogenic activities can subject fish to rapid changes in these important environmental variables. These rapid changes in temperature and oxygen (generally referred to as temperature or oxygen shock) may have sub‐lethal consequences depending upon the magnitude and the fish species. This study quantified physiological changes in largemouth bass, Micropterus salmoides (Lacepède), exposed to two levels of heat and cold shocks and to two levels of hypoxic and hyperoxic shocks. Following a cold shock from 20 °C to 8 °C, plasma cortisol and glucose increased after 1 h and lactate dehydrogenase activity increased after 6 h. Plasma glucose and K⁺ concentrations increased 1 h after a heat shock from 20 °C to 32 °C but not after 6 h. Bass subjected to a hypoxic shock from 8 to 2 mg O₂ L^?1 showed decreased plasma K⁺ and increased plasma glucose and white muscle lactate. No changes in physiological parameters were observed in bass subjected up to 18 mg O₂ L^?1 hyperoxia. Results from this study suggest that largemouth bass can tolerate a wide range of temperature and oxygen shocks, but temperature decreases of 20 to 8 °C and hypoxia as low as 4 mg O₂ L^?1 should be avoided to minimise physiological perturbations.     

The physiological response of the turbot to multiple net confinements

The effects of multiple net confinements on the physiological stress response of the turbot (Scophthalmus maximus L.) were investigated. To allow for repeated blood sampling from individuals, fish were cannulated in the afferent branchial artery and were exposed to multiple 9 min net confinement episodes separated by either 4 h or 24 h. In fish stressed twice 4 h apart cumulative effects in plasma cortisol, glucose and free fatty acid concentrations were evident after the second handling stress. Although plasma Na⁺ and Cl⁻ concentrations were not increased further by the second net confinement, the elevation in plasma concentrations were more sustained compared to turbot handled only once. In a second experiment where turbot were net confined five times, with a 24 h recovery period between each net confinement episode, there was no evidence of any physiological accommodation with repeated exposures. For most circulatory parameters, there was also no evidence of any cumulative effect apparent. Plasma glucose concentrations were, however, elevated to a significantly higher degree with repeated net confinements. Although turbot were tolerant to the handling procedures, with no mortalities recorded, episodes of multiple handling of this species should be separated by at least 24 h if cumulative physiological disturbances are to be avoided. The significance of cumulative increases in plasma glucose concentrations is discussed. Present address: Aquaculture Associates International, The Firs, Glasshouse Hill, Codnor, Derbyshire, DE5 9QT, UK     

Recovery from nitrite-induced methaemoglobinaemia and potassium balance disturbances in carp

The ability of carp to recover from nitrite-induced methaemoglobinaemia and disturbances in potassium balance and cell volume was studiedin vivo andin vitro. Nitrite accumulated to a plasma concentration of 3 mM during 2 days of nitrite exposure was eliminated from the plasma within 2–3 days in clean water. The nitrite-induced methaemoglobinaemia disappeared after 3 days of recovery. During nitrite exposure, K⁺ was lost from the red blood cells (RBCs) and from skeletal muscle tissue, which led to reduced cell volume and an extracellular hyperkalaemia. Extracellular [K⁺] rose less than predicted if lost K⁺ had remained in the extracellular space, suggesting further transport of K⁺ to the environment. The intracellular K⁺ and water content were restored after few days of recovery in clean water, but this was paralleled by development of an extracellular hypokalaemia. This shows that intracellular K⁺ balance was reestablished at the expense of the extracellular compartment, and supports that an overall K⁺ deficit resulted from K⁺ loss to the environment during nitrite exposure. Ventricle tissue differed from skeletal muscle and RBCs by not loosing K⁺ and by having increased sodium and water contents during nitrite exposure. These changes were corrected by recovery in nitrite-free water. In vitro addition of nitrite to blood with low O₂ saturation induced metHb formation and RBC K⁺ efflux. Subsequent reduction of metHb to functional Hb was similar in blood with low and high O₂ tension. A net re-uptake of K⁺ was observed only in RBCs with low O₂ saturation and when metHb reached low values.     

Respiratory stress in rainbow trout dying from aluminium exposure in soft,acid water,with or without added sodium chloride

Rainbow trout exposed to 32 μM aluminium at pH=5.0 in artificial soft water ([Ca⁺⁺]=50 μM), with or without added sodium chloride (150 mM), suffer from severe respiratory stress characterized by hyperventilation, low Pa_{O 2}, high Pa_{CO 2}, low pHa and high blood lactate concentrations at death. Plasma chloride concentration at death had decreased in the group with no added NaCl, but not in the presence of added NaCl. Median survival times were not significantly different in the two groups. These findings suggest that death under the given conditions is primarily due to impeded gas exchange.     

Incorporation and metabolism of14C-labelled polyunsaturated fatty acids in wild-caught juveniles of golden grey mullet,Liza aurata,in vivo

The incorporation, and the capacity for desaturation and elongation in vivo, of intraperitoneally-injected,¹⁴C-labelled n-3 and n-6 C₁₈ and C₂₀ polyunsaturated fatty acids (PUFA) were investigated in juvenile golden grey mullet,Liza aurata. The results indicate that juvenile mullet have only limited ability to convert C₁₈ polyunsaturated fatty acids to C₂₀ and C₂₂ highly unsaturated fatty acids (HUFA)in vivo. This suggests that juvenile golden grey mullet require the provision of preformed C_20/22 HUFA, such as eicosapentaenoic and docosahexaenoic acids, in the diet. The impairment in the desaturase/elongase pathway was similar to that found in turbot,Scophthalmus maximus, and gilthead sea bream,Sparus aurata, being primarily at the level of Δ5-desaturase. The data from the largely herbivorous golden grey mullet juveniles are consistent with the hypothesis that marine fish in general, irrespective of dietary habits, have limited capacity for the desaturation and elongation of C₁₈ PUFA. The defect in Δ5-desaturase activity combined with the consistent finding that arachidonic acid is selectively incorporated and retained in membrane phosphatidylinositol suggests that, like turbot and gilthead sea bream, golden grey mullet may also have a requirement for preformed arachidonic acid in the diet.     

Influence of sampling methods and anaesthetization on various haematological parameters of several teleosts

Effects of blood sampling procedure on various haematological parameters were investigated in four Baltic teleost species. In pike, parameters in samples from permanently cannulated and thus minimally disturbed specimens were used as a standard. Blood lactate and plasma K⁺ concentrations were the most labile. Because of the reduced muscular activity and shorter sampling time, blood from fish immobilized by stunning gave a better picture of the resting state than samples from anaesthetized fish. Incubation of venous blood under falling O₂ tension (sample ageing) caused a rapid change in plasma K⁺ concentration. For reliable plasma K⁺ values immediate centrifugation of blood samples is necessary.     

Does Amia Calva aestivate?

During gradual air exposure, Amia calva show no reduction in oxygen consumption, no increase in plasma urea levels or in urea excretion. Blood pH remains constant, and plasma total CO₂, P_{CO 2}, HCO₃ ^-. total ammonia and NH₃ concentrations all rise significantly. Exposure to 923 μmol/l NH₄Cl does not elicit an increase in urea production or airbreathing. Aquatic hypoxia without access to air does not cause a reduction in aerobic metabolism, and moderate levels result in death. These results suggest that Amia are incapable of aestivation, due to an inability to detoxify ammonia to urea and reduce metabolism, and die following three to five days of air exposure.     

Oxygen uptake in the Antarctic teleost Pagothenia borchgrevinki. Limitations imposed by X-cell gill disease

Fish in a population of Pagothenia borchgrevinki in McMurdo Sound, Antarctica, are affected by a gill disease (X-cell disease) which causes tissue hyperplasia that results in a decreased gill surface area and an increased water/blood diffusion distance. P. borchgrevinki acquires 95% of its oxygen via the gills, but damage to the gills by X-cell disease did not affect this function. There was no compensatory shift to cutaneous respiration. X-cell disease reduced the ability for oxygen uptake at low ambient P_{O 2} and the decreased uptake was related to the extent of the disease. _{O 2} max was greatly reduced in X-cell affected fish and substantially reduced their aerobic potential. This effect may impair the ability of diseased fish to catch prey and avoid predators.     

Effects of cold acclimation and storage temperature on crucian carp (Carassius auratus gibelio) in a waterless preservation

The research aims to explore the impact of cold acclimation and storage temperature on crucian carp in a waterless preservation. It is conducted by studying the influence of cold acclimation on crucian carp in temperatures of 5 and 1 °C h^?1, followed by having them preserved under waterless conditions at 4 and 0 °C for 24 h to analyze their aerobic and anaerobic capacities. The research findings revealed that the temperature drop at 1 °C h^?1 is conducive to preserving the activity of lactate dehydrogenase. The activity of isocitrate dehydrogenase was maintained, and the brain succinate dehydrogenase remained unchanged. With regards to alanine transaminase, its activity, being sensitive to the changes of storage temperatures, was maintained when the temperature was decreased to 0 °C and malondialdehyde was accumulated at the same temperature. Stored in cold environment, blood catalase was accumulated; however, obvious changes were not found in the liver. It is likely that cold acclimation contributes to retaining aerobic and anaerobic metabolism under waterless preservation as well as decreasing the damage of blood oxidation.     

Can the mudskipper,Periophthalmus chrysospilos,tolerate acute environmental hypoxic exposure?

The mudskipper P. chrysospilos became inert at 0.76 μl O₂.ml⁻¹ when it was allowed to respire in a ‘closed respiratory chamber’. No ethanol was detected although it excreted three times more total carbon dioxide into the surrounding sea water than the amount of oxygen consumed. However, P. chrysospilos could survive environmental hypoxic exposure (0.8 μl O₂.ml⁻¹) for at least 6 h. Upon normoxic recovery, the oxygen debt repayment was only a small fraction of the oxygen deficit incurred during the 6 h of hypoxic exposure. It would therefore appear that P. chrysospilos was able to cope with environmental hypoxia by suppressing its metabolic rate.