Characterization and expression of NADPH oxidase genes in stimulated splenic neutrophils of tilapia,Oreochromis niloticus by a mix of traditional Chinese medicine and Bacillus species (TCMBS)

Traditional Chinese medicine and Bacillus species (TCMBS) mixture is an immunostimulant with considerable promise as an alternative in improving fish health. However, nothing is known on its effects on the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase genes and production of reactive oxygen species (ROS) in the neutrophils of fish. The full lengths of tilapia phagocytic NADPH oxidase genes gp91^phox, p22^phox, p40^phox, p47^phox, and p67^phox were cloned and their expression profiles after TCMBS stimulus investigated. The cDNAs of tilapia gp91^phox, p22^phox, p40^phox, p47^phox, and p67^phox contained open reading frames of 1698 bp, 561 bp, 1053 bp, 1584 bp, and 1470 bp respectively, encoding 561, 186, 350, 527, and 489 amino acids respectively. Comparison of the deduced amino acid sequences showed that tilapia NADPH oxidase genes shared 58%–91% and 21%–67% identity with those of other teleost and mammals respectively. Besides, tilapia NADPH oxidase genes contain conserved domains and motifs required for ROS generation. Phylogenetic analysis suggested tilapia NADPH oxidase genes were close to those of Fundulus heteroclitus. After 2 weeks of TCMBS application showed significant upregulation in expression of NADPH oxidase genes, antioxidant genes (i.e., superoxide dismutase, catalase, and glutathione‐disulphide reductase), and an increase in the production of ROS compared to the control in splenic neutrophils of tilapia. Collectively, our study provides evidence of the structure of tilapia NADPH oxidase genes and demonstrate that TCMBS application could modulate their activity in neutrophils to improve immunity in tilapia.     

Comparative study of the intracellular superoxide anion production in different penaeid species through the NBT‐reduction assay

The capacity of reactive oxygen intermediates production upon haemocyte stimulation is one of the most important immunoparameter utilized to assess the health status in cultivated shrimps. In the present study, we compared oxidative stress potential, by measuring the superoxide anion production in three penaeid shrimps: two wild Atlantic species, the pink shrimp Farfantepenaeus paulensis and the white shrimp Litopenaeus schmitti and one cultivated Pacific species, the white shrimp, Litopenaeus vannamei, through the nitro‐blue‐tetrazolium‐reduction assay. We also proposed an optimized experimental protocol for this assay, that produces rapid and consistent results with low levels of basal superoxide anion (O₂^?) production by unstimulated haemocytes and high levels of this oxygen radical after cell stimulation. Among the different cell elicitors used (zymosan, laminarin, lipopolysaccharide and phorbol myristate acetate), laminarin (β‐1,3‐glucans – 2 mg mL^?1) was the most potent cell activator for the haemocytes of all three penaeids and we recommend this immunostimulant to routinely evaluate shrimp respiratory burst. In general terms, the most elevated levels of O₂^? production, after cell stimulation with microbial components, were detected in L. schmitti. Interestingly, the stimulation profile of the haemocytes of L. vannamei was more similar to F. paulensis, than to L. schmitti, which is more phylogenetically related.     

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Oxygen-transfer rates (tap water, 0 mg/l dissolved oxygen, 20°C) for four tractorpowered emergency aerators tested in a 820-m³ pond were: blower-fan aerator, 12.2 kg O₂/h; Crisafulli^® pump and sprayer, 12.3 kg O₂/h; Airmaster^® aerator (centrifugal pump and sprayer), 21.3 kg O₂/h; paddlewheel aerator, 26.3 kg O₂/h. Times required for aerators to homogeneously mix salt in a 6000-m³ pond were: blower-fan aerator, 96 min; Crisafulli pump and sprayer, 94 min; paddlewheel aerator, 53 min; and Airmaster aerator, 38 min. The Airmaster aerator and the paddlewheel aerator did not differ in their abilities to transfer oxygen and circulate pond water (P > 0.05); they were both superior to the blower-fan aerator and the Crisafulli pump and sprayer (P < 0.01).     

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.     

Effect of body size on organ-specific mitochondrial respiration rate of the largemouth bronze gudgeon

The effects of body size on the mitochondrial respiration rate were assessed in the heart, brain, gill, liver, and red muscle of largemouth bronze gudgeon, Coreius guichenoti, from the Yangtze River. Body mass had a significant influence on the state 3 oxygen consumption rate of the mitochondria from the heart, gill, and red muscle. The relationships between body mass (M, g) and state 3 oxygen consumption rate (V _{state 3}, nmol O min^?1 mg^?1) of the mitochondria were represented by the following: V _{state 3} = 3.56M ^0.71 for heart, V _{state 3} = 4.64M ^0.50 for red muscle, and V _{state 3} = 473.73M ^?0.82 for gill. There was a significant difference in V _{state 3} , V _{state 4}, and respiratory control ratio among organs and all were highest in the heart. Our results suggest that the relationship between mitochondrial respiratory rate and body size varies among organs. The high mitochondrial respiratory rate in the heart of the largemouth gudgeon suggests that it has the highest oxidative capacity.     

Effect of low dissolved oxygen on the oxygen consumption rate and rhythm of the mudskipper Scartelaos gigas (Pisces, Gobiidae)

The mudskipper Scartelaos gigas is expected to experience repeated severe hypoxia in its environment. Hence, we conducted experiments on the oxygen consumption rate (OCR) and OCR rhythm of S.?gigas at low graded dissolved oxygen (DO) levels, without access to atmospheric air, to estimate its tolerance to hypoxia. A dominant circadian OCR rhythm was observed at the control DO level of 6.96?C7.78?mg?O₂/l. This rhythm was unchanged until 2.06?mg?O₂/l, even though the amplitude of the peak was somewhat diminished at 2.06?C2.87?mg?O₂/l. The OCR rhythm amplitude was greatly diminished and the rhythm period was also greatly changed at 1.23?C2.05?mg?O₂/l. Nevertheless, the mean OCR (0.11?ml?O₂/g WW/h) at 1.23?C2.05?mg O₂/l was similar to that of control (0.12?ml O₂/g?WW/h). Thus, the weakness and period change of the OCR rhythm kept the metabolic rate level similar to control. These results suggest that S.?gigas does not have normal metabolic activity at 1.23?C2.05?mg O₂/l but barely manages to endure this DO level as a pre-emergency state. This species could be inhibited under a longer maintenance period at DO level of 1.23?C2.05?mg?O₂/l or still lower. It can be concluded that S.?gigas is quite tolerant to low DO environment and may have a specific strategy for such tolerance.     

Changes in arterial PO₂, physiological blood parameters and intracellular antioxidants in free-swimming Atlantic cod (Gadus morhua) exposed to varying levels of hyperoxia

Free-swimming Atlantic cod (Gadus morhua) were exposed to water oxygen pressures (P _wO₂) ranging from 18.1 to 41.5 kPa and sampled for blood using an indwelling caudal artery cannula. Arterial blood oxygen pressure (P _aO₂) increased with increasing P _wO₂, from 12.0 kPa in normoxia (18.1 kPa) to 34.2 kPa in the highest hyperoxic level tested (41.5 kPa). Blood CO₂ pressure and plasma bicarbonate concentration increased with P _wO₂, indicating reduced ventilation with increased P _wO₂. Plasma glucose, sodium and potassium were not affected by water oxygen level. Blood oxidative stress biomarkers, reduced glutathione, oxidized glutathione and the oxidative stress index (ratio between oxidized and total glutathione) differed intermittently between normoxia and hyperoxia. The oxidative stress index was higher in the blood of exposed compared to unexposed control cod. Together with elevated P _aO₂, these findings suggest increased production of reactive oxygen species and increased oxidative stress in Atlantic cod exposed to hyperoxia.     

Morphological studies of peripheral blood cells of the Chinese sturgeon, <Emphasis Type="Italic">Acipenser sinensis</Emphasis>

The peripheral blood cells of one-year-old Chinese sturgeon (Acipenser sinensis) have been studied by light microscopy and transmission electron microscopy. The erythrocyte count was 84.86 × 10⁴ cell mm⁻³ in the peripheral blood of the fish and that of leukocytes was 2.24 × 10⁴ cell mm⁻³. The erythrocytes and four main types of leucocyte—thrombocytes, lymphocytes, granulocytes (including neutrophils and eosinophils), and monocytes, were identified in the peripheral blood. In addition to normal erythrocytes, reticulocytes and division of erythrocytes were observed. Thrombocytes were the most numerous among the leukocytes, and the number of neutrophils with lobated nuclei was larger than for other fish. The structures of the erythrocytes, lymphocytes, monocytes, granulocytes, and thrombocytes of the fish were studied. The erythrocytes were almost completely devoid of organelles, except for some mitochondria and granules. A large number of vacuoles and a few organelles were observed in cytoplasm of the monocytes. There were many microvilli on the membrane and pseudopodia-like cytoplasm bulge in the lymphocytes. The neutrophils were round or oval in shape with bilobed, trilobed, or multilobed nuclei whereas the eosinophils had big special granules, dark stained. There were many vesicles in some thrombocytes, which were related to its phagocytosis; some thrombocytes had almost no cytoplasm or organelles.     

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 effect of irradiance and temperature on the photosynthesis of two agarophytes Gelidium elegans and Pterocladiella tenuis (Gelidiales) from Kagoshima,Japan

The effect of irradiance and temperature on the photosynthesis of two Japanese agarophytes, Gelidium elegans and Pterocladiella tenuis (Gelidiales), was determined using dissolved oxygen sensors and pulse amplitude modulated (PAM) fluorometry. Gross photosynthesis and dark respiration rates were determined over a range of temperatures (8–36 °C). The highest gross photosynthetic rates were 40.3 and 37.0 mg O₂ g _ww ^?1  min^?1 and occurred at 24.3 and 25.5 °C [95 % Bayesian credible interval (BCI) 20.7–28.0 and 23.4–28.3 °C], respectively. The dark respiration rate in G. elegans and P. tenuis increased with increasing temperature at a rate of 0.10 and 0.31 mg O₂ g _ww ^?1  min^?1 °C^?1 , respectively. Modeling the net photosynthesis–irradiance (P–E) responses of G. elegans and P. tenuis at 20 °C revealed that the net photosynthetic rates quickly increased at irradiance levels below the estimated saturation irradiance of 88 and 83 µmol photons m^?2 s^?1, with a compensation irradiance of 14 and 19 µmol photons m^?2 s^?1, respectively. The highest value of the maximum effective quantum yield (Φ _PSII) occurred at 20.1 °C (BCI 18.9–21.5 °C) and 21.3 °C (BCI 20.2–22.5 °C) for G. elegans and P. tenuis and was 0.49 and 0.45, respectively. These optimal temperatures of Φ _PSII were relatively lower than those determined by the photosynthesis–temperature model of oxygen evolution. The temperature response of these species indicates that they are probably well adapted to the current range of seawater temperatures in the study site but that they are near the boundary of their tolerable limits.     

Oxygen consumption and ammonia excretion of common wolffish Anarhichas lupus Linnaeus 1758 in an experimental-scale, seawater, land-based culture system

The oxygen consumption (0₂) and ammonia excretion (N) of juvenile and adult common wolffish was measured in culture tanks in the laboratory. The oxygen consumption and ammonia excretion were affected by temperature (C), fish size and feeding rate. For juveniles (0.5 kg; 7C) the diel oxygen consumption rate varied between 37 and 62 mg O₂ kg^-1 h^-1 and ammonia excretion between 2.3 and 5.7 mg N kg^-1 h^-1. The corresponding rates for adult fish (6.9 kg; 7C) were 29-44 mg O₂ kg^-1 h^-1 and 1.2–3.1 mg N kg^-1 h^-1. The weight-specific oxygen consumption (mg O₂ kg^-1 h^-1) was described by the following formulae: O₂ (7C) = 0.17* W^0.83 and O₂ (12C) = 0.39 * W^0.73 and the corresponding ammonia excretion (mg N kg^-1 h^-1) by: N(7C) = 0.024 W^0.75 and N(12C) = 0.073 W^0.60, where W is fish weight in g.     

Short communication: Acute toxicity of hydrogen peroxide in juvenile white shrimp Litopenaeus vannamei reared in biofloc technology systems

Biofloc technology (BFT) has been used to rear white shrimp, Litopenaeus vannamei. In this culturing system, the absence of aeration causes a rapid drop in dissolved oxygen levels, and hydrogen peroxide (H₂O₂) can be used as an emergency source of oxygen. This study aimed to determine the lethal concentration and safe level of H₂O₂ applied as a source of oxygen for juvenile white shrimp L. vannamei in a BFT system. Juveniles (1.39 ± 0.37 g) were exposed for 2 h to different concentrations of H₂O₂ [29 (100), 58 (200), 116 (400), 174 (600), 232 (800), 290 (1,000) and 348 (1,200) μL H₂O₂/L (ppm H₂O₂-29 %/L)] in addition to a control group without addition of H₂O₂, and the survival rates were monitored for 96 h. The LC₅₀ values and 95 % confidence intervals at 24, 48, 72 and 96 h were 235.5 (207–268), 199.1 (172–229), 171.1 (146–198) and 143.3 (120–170) μL H₂O₂/L, respectively. The safe level was 14.3 μL H₂O₂/L, and the highest concentration with survival rates similar to the control group (NOAEC) was 29 μL H₂O₂/L. In these concentrations, H₂O₂ can be used as a safe source of oxygen for L. vannamei reared in BFT systems.     

Effect of temperature decrease on hemocyte apoptosis of the white shrimp Litopenaeus vannamei

This study investigated the effect of continuous temperature decrease on hemocyte apoptosis of the white shrimp Litopenaeus vannamei. In the stress group, water temperature decreased from 26 to 17 °C at a rate of 1 °C/h. Shrimp kept at 26 ± 0.5 °C were used as control group. Total hemocyte count (THC), reactive oxygen species (ROS) production, cytoplasmic free-Ca²⁺ (CF-Ca²⁺) concentration, mitochondrial membrane potential (MMP), apoptotic cell ratio, and caspase-3 activity of L. vannamei hemocytes were determined when water temperature decreased to 23, 20, and 17 °C, respectively. Increased ROS production in hemocytes was observed when water temperature decreased to 20 and 17 °C. Decreased THC and cellular MMP, increased CF-Ca²⁺ concentration, apoptotic cell ratio, and caspase-3 activity were shown when water temperature decreased to 17 °C. These results indicate that water temperature decrease can induce oxidative stress on shrimp hemocytes and then cause mitochondria and caspase-3 mediated hemocyte apoptosis and THC reduction, when water temperature decreased to an unconformable level.     

Hydrogen peroxide oxygenation and disinfection capacity in recirculating aquaculture systems

Hydrogen peroxide (H₂O₂) treatment is an alternative for disinfection in aquaculture, which may be advantageous as it dissociates and disinfects while increasing water oxygen concentration. Yet, accurate dosing remains undeveloped in Recirculating Aquaculture Systems (RAS). Dosage requirements can depend on organic burden, stocking density, feeding frequency, salinity, temperature and biofilter performance. The present case study investigated the dual effect of H₂O₂ application for oxygen enrichment and disinfection when continuously applied to a RAS rearing European seabass. H₂O₂ addition equivalent to 2.4 and 15.8 H₂O₂ mg L⁻¹ were applied for 4 h per day in three 5-days experiments. H₂O₂ was injected at the inlet of protein skimmer and/or the rearing tanks in or without combination with traditional disinfection methods. Water microbial load and oxygen saturation were determined, along with stress markers glucose and cortisol in blood plasma of fish. Doses of 15.8 mg L⁻¹ H₂O₂ steadily increased oxygen levels in holding tank water from ∼50 % to over 100 % saturation while reducing microbial load (from 604.4 CFU ml⁻¹ in the rearing tanks before dosing to 159.8 CFU ml⁻¹ after application), achieving suitable conditions for commercial fish densities in RAS. The doses used had negligible impact on biofilter performance and did not affect the fish in terms of stress. Overall results indicate H₂O₂ is effective for disinfection and oxygenation of RAS systems when applied at appropriate dosage and we recommend the protein skimmer as the safest position in order to protect the bacterial community of the biofilters and the reared fish.     

The pond's shape matters: differential growth,physiological condition and survival of epibenthic Farfantepenaeus aztecus postlarvae

As a function of the water quality provided by square, circular and oval experimental ponds, the growth, survival and oxygen requirements in epibenthic postlarvae of Farfantepenaeus aztecus were analysed in relation to their routine metabolism and apparent heat increment. Temperature, oxygen concentration, pH and salinity were measured daily in two experimental ponds of each shape. The postlarvae oxygen consumption during two 24‐h cycles, their growth, physiological condition and survival and the productivity in the ponds were estimated. Low values of pH, oxygen concentration and phytobenthos productivity, and reduced postlarvae relative growth and survival were observed in the square ponds. We suggest that the latter results from a deficient water circulation related to the effect of the pond's shape on dissolved oxygen levels and, consequently, on growth and survival. The postlarvae routine metabolism, including feeding, varied between 1.91 and 2.25 mg O₂ h^?1 g^?1 wet weight, whereas the minimum oxygen concentration needed in the ponds is approximately 4.25 mg O₂ L^?1. These conditions were achieved in the oval ponds concurrent with higher survival and growth values, in which individuals distributed randomly, for which we suggest that oval‐shaped ponds could be the most adequate for the culture of this and other penaeid species.     

Practical use of response surface methodology for optimization of veterinary antibiotic removal using UV/H2O2 process

Three of the most commonly used veterinary antibiotics—enrofloxacin (ENR), sulfamethoxazole (SMX), and oxytetracycline (OTC)—were chosen as representative antibiotics for UV/H₂O₂ treatments. The objective was to determine the optimization of UV/H₂O₂ to remove antibiotics from aquaculture discharge water using response surface methodology. The degradation of the antibiotics was investigated under varying UV/H₂O₂ conditions in environments with different levels of pH, water matrices, humic acid, and constituent ions. The degradation results demonstrated that increasing the H₂O₂ dosage facilitated ENR degradation at a neutral pH while facilitating degradation of SMX and OTC at a slightly acidic pH. The optimum removal conditions for ENR, which was used in all influential effect experiments and the contact tank experiments, was obtained at 10 mM H₂O₂, a pretreated COD of 87.51 mg L⁻¹, and an initial pH of 6.15. Among the tested anions, only the presence of Cl^- showed slight positive effects on ENR degradation, due to the generation of secondary active radicals. During the reaction, the hydroxyl radical (OH) was present at a higher pH while singlet oxygen (¹O₂) was slightly present at a lower pH. The experimental results from H₂O₂ sequential addition indicated that freshly added H₂O₂ could quench the recently generated OH and therefore a high H₂O₂ concentration with frequent adding was not necessary. Our contact system reduced the ENR concentration in both the effluent reservoir and in the UV irradiation zone. The overall results supported the use of the UV/H₂O₂ system to treat remnant antibiotics in the discharge water.     

The effect of temperature on the resting and post-exercise metabolic rates and aerobic metabolic scope in shortnose sturgeon <Emphasis Type="Italic">Acipenser brevirostrum</Emphasis>

The effects of acclimation temperature (15, 20, 25 °C) on routine oxygen consumption and post-exercise maximal oxygen consumption rates (MO₂) were measured in juvenile shortnose sturgeon (Acipenser brevirostrum LeSueur, 1818). The routine MO₂ of shortnose sturgeon increased significantly from 126.75 mg O₂ h^?1 kg^?1 at 15 °C to 253.13 mg O₂ h^?1 kg^?1 at 25 °C. The temperature coefficient (Q ₁₀) values of the routine metabolic rates ranged between 1.61 and 2.46, with the largest Q ₁₀ values occurring between 15 and 20 °C. The average post-exercise MO₂ of all temperature groups increased to a peak value immediately following the exercise, with levels increasing about 2-fold among all temperature groups. The Q ₁₀ values for post-exercise MO₂ ranged from 1.21 to 2.12, with the highest difference occurring between 15 and 20 °C. Post-exercise MO₂ values of shortnose sturgeon in different temperature groups all decreased exponentially and statistically returned to pre-exercise (resting) levels by 30 min at 15 and 20 °C and by 60 min at 25 °C. The aerobic metabolic scope (post-exercise maximal MO₂-routine MO₂) increased to a maximum value ～156 mg O₂ h^?1 kg^?1 at intermediate experimental temperatures (i.e., 20 °C) and then decreased as the temperature increased to 25 °C. However, this trend was not significant. The results suggest that juvenile shortnose sturgeon show flexibility in their ability to adapt to various temperature environments and in their responses to exhaustive exercise.     

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.     

Characterization of whitebait (Galaxias maculatus) respiratory rates to optimize intensive culture carrying capacities

Galaxias maculatus is an osmeriform native fish of the Southern Hemisphere, in which the crystalline larvae is considered as a luxury delicacy, for this reason, it has been commercially exploited in Chile, Argentina and New Zealand. However, the fisheries have been rapidly decreasing due to the overexploitation and the predation of introduced species. Because of these events, there is a need to determine a carrying capacity for an intensive fish culture. In order to optimize stocking densities for fish culture, this paper proposes objectives to determine oxygen consumption (OC) rates, dissolved oxygen concentrations that produce signs of hypoxia and the average time elapsed between food intake and peak OC in G. maculatus. In the oxygen experiments under routine metabolism conditions, we found that G. maculatus adults and whitebait showed signs of asphyxia at dissolved oxygen concentrations between 1.3 and 2.2 mg L^?1 and that adults tolerated dissolved oxygen levels as low as 1.3 mg L^?1. The results showed that G. maculatus individuals with an average weight of 0.04 g consumed 0.048 mg O₂ h^?1, whereas individuals with an average weight of 1.4 g consumed 0.345 mg O₂ h^?1. Galaxias maculatus increased the OC rate by 31%, from 0.39 to 0.51 mg O₂ h^?1 g^?1, occurring 14 min after food intake. The carrying capacities for industrial cultures of G. maculatus, were estimated using an allometric equation (OC=0.2363 ×W ^0.612 ), a water flow rate of 1 m³ h^?1 and an input oxygen concentration of 10 mg L^?1 at 12 °C. The density culture of whitebait (4 g) can be allowed to reach 8–11 kg m^?3; therefore, these stocking densities reduce the risk of hypoxia and mortality, ensuring the appropriate growth and feed conversion rates.     

Aquaculture development in less developed countries: Social,economic and political problems: Leah J. Smith and Susan Peterson. Bowker Publishing Company,Essex, U.K., 1982. 152 pp., US$ 29.50. ISBN 0-86531-235-4

Oxygen consumption and ammonia production in elvers of varying growth rates were studied. The allometric equation describing the relationship between oxygen consumption and weight is y =00.638 x^0,525, where y is the oxygen consumption (mg/h) and x is the mass (g). The weight specific allometric equation for the relationship between ammonia excretion and weight is $\text{y}\text{x}\text{= 0.0129 x}{}^{\mathrm{0,465}}$. Slow growing elvers were found to have higher respiratory rates (0.737 mg O₂ h^?1 g^?1) than would be expected for their size.