Temperature effect on heart rate of jack mackerel Trachurus japonicus during swimming exercise

The heart rate of jack mackerel [16.5–21.2 cm fork length (FL), n = 24] was examined through forced swimming exercise in a flume tank by 10-min step-ups of speed levels in 1.5–6.0 FL/s range at different temperatures of 10, 15, and 22 °C. Electrocardiograph (ECG) monitoring was conducted by comparing the heartbeat pattern in still water without flow as a control, and continuously during exercise by speed levels until fatigue and during the recovery phase. Average heart rates in the control at each temperature were 36.5 beats/min at 10 °C, 56.1 beats/min at 15 °C, and 75.2 beats/min at 22 °C. The heart rate of jack mackerel significantly increased as the swimming speed was increased in each temperature. At the lower swimming speed of 1.5–2.4 FL/s, the heart rate was the same level as the control value at each respective temperature. The heart rate started to increase at swimming speeds of 2.3–2.5 FL/s at all temperatures. The higher heart rate in the range of 150–200 beats/min was achieved at a swimming speed of 6.0 FL/s at 22 °C. The recovery time after the maximum heart rate at high speed became longer at high temperatures.     

Fatigue analysis of the jack mackerel <Emphasis Type="Italic">Trachurus japonicus</Emphasis> by electrocardiographic monitoring during prolonged swimming

The effect of fatigue on swimming performance was examined by measuring the swimming endurance time and heart rate of the jack mackerel Trachurus japonicus [15.7 ± 0.8 cm fork length (FL), n = 15] during forced exercise in a flume tank at fixed swimming speeds of 4, 5 and 6 FL/s. Electrocardiographic (ECG) monitoring during the experimental process from control (0.8 FL/s) to exercise phase revealed a rapid cardiac response of T. japonicus to the elevation of swimming speed. The heart rate of T. japonicus significantly increased from the control level of 52.9 beats/min at a slow flow speed of 0.8 FL/s to 148.2 beats/min at 4 FL/s, 168.6 beats/min at 5 FL/s and 183.2 beats/min at 6 FL/s. During the fixed speed test, the heart rate of each individual fish was stabilized without any recognizable increase or decrease until the fish failed to swim because of fatigue. Fatigue analysis on endurance time demonstrated that prior swimming experience at prolonged speeds would impair the endurance performance during subsequent swimming exercise. Recovery time of the heart rate after the fish was fully exhausted by prolonged fast exercise increased with increasing swimming endurance time.     

圆口铜鱼幼鱼可持续游泳能力及活动代谢研究

以圆口铜鱼(Coreius guichenoti)幼鱼为研究对象,通过自制的鱼类游泳实验装置,测定了4个温度(10,15,20和25℃)下圆口铜鱼幼鱼游泳速度达到临界游速过程中及运动疲劳后耗氧率的变化情况;在自然水温条件下,测定了5个不同流速下的可持续游泳时间,并通过摄像记录分析了不同游泳速度下的游泳行为。结果显示:圆口铜鱼幼鱼在运动疲劳前耗氧率随流速的增加显著上升(P0.05),在临界游速时达到峰值;运动疲劳后耗氧率逐渐下降,40~50 min内耗氧率恢复至低流速时的水平。自然水温(18.0±1.5)℃条件下幼鱼的可持续游泳时间随流速增加逐渐减小(P0.01),在1.31倍临界游速的固定流速下,平均可持续游泳时间达29 min,体现了较强的游泳耐力及无氧代谢能力。录像分析表明,摆尾频率(TBF)与游速的关系呈线性正相关(P0.001),且随着温度升高,TBF随流速增加的趋势越明显。     

Effect of temperature on excess post-exercise oxygen consumption in juvenile southern catfish (<Emphasis Type="Italic">Silurus meridionalis</Emphasis> Chen) following exhaustive exercise

The effects of temperature on resting oxygen consumption rate (MO_2rest) and excess post-exercise oxygen consumption (EPOC) after exhaustive exercise (chasing) were measured in juvenile southern catfish (Silurus meridionalis) (8.40 ± 0.30 g, n = 40) to test whether temperature has a significant influence on MO_2rest, maximum post-exercise oxygen consumption rate (MO_2peak) and EPOC and to investigate how metabolic scope (MS: MO_2peak − MO_2rest) varies with acclimation temperature. The MO_2rest increased from 64.7 (10°C) to 160.3 mg O₂ h⁻¹ kg⁻¹ (25°C) (P < 0.05) and reached a plateau between 25 and 30°C. The post-exercise MO₂ in all temperature groups increased immediately to the peak values and then decreased slowly to a steady state that was higher than the pre-exercise MO₂. The MO_2peak did not significantly differ among the 20, 25 and 30°C groups, though these values were much higher than those of the lower temperature groups (10 and 15°C) (P < 0.05). The duration of EPOC varied from 32.9 min at 10°C to 345 min at 20°C, depending on the acclimation temperatures. The MS values of the lower temperature groups (10 and 15°C) were significantly smaller than those of the higher temperature groups (20, 25 and 30°C) (P < 0.05). The magnitude of EPOC varied ninefold among all of the temperature groups and was the largest for the 20°C temperature group (about 422.4 mg O₂ kg⁻¹). These results suggested that (1) the acclimation temperature had a significant effect on maintenance metabolism (as indicated by MO_2rest) and the post-exercise metabolic recovery process (as indicated by MO_2peak, duration and magnitude of EPOC), and (2) the change of the MS as a function of acclimation temperature in juvenile southern catfish might be related to their high degree of physiological flexibility, which allows them to adapt to changes in environmental conditions in their habitat in the Yangtze River and the Jialing River.     

Effects of soft-water acclimation on the physiology, swimming performance, and cardiac parameters of the rainbow trout, Oncorhynchus mykiss

Rainbow trout acclimated to soft water were submitted to an incremental velocity trial, and exhibited a 14% decrease in critical swimming speed (U _crit ∼ 1.37 ± 0.055 vs. 1.54 ± 0.044 m s⁻¹) compared to fish kept in hard water. After a standardized swimming protocol, soft-water-acclimated fish had higher blood lactate concentrations (6.5 ± 0.66 and 6.0 ± 0.64 mmol L⁻¹ (soft water) vs. 5.0 ± 0.46 and 3.9 ± 0.32 mmol L⁻¹ (hard water)), revealing a greater use of anaerobic metabolism for the same exercise. Cardiovascular parameters were investigated while fish were swimming at increasing water velocities, revealing that soft-water-acclimated fish had lower increases in heart rate (105% vs. 118% of pre-exercise values), due to higher heart rates observed during acclimation and during the first 10 min of the swimming trial. This was also reflected by the plateau in heart rate and stroke volume observed during the swimming protocol, which can be attributed to increased cardiovascular function in response to soft-water acclimation. These results are in accord with previously reported increases in blood-to-water diffusion distance, due to proliferation of chloride cells at the gills in response to soft-water conditions, and underscore the costs and limitations of soft-water acclimation. R. C. Playle—Deceased.     

Effect of gamma-aminobutyric acid and porcine growth hormone on survival of the euryhaline rotifers <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> sp. complex preserved at low temperature

Gamma-aminobutyric acid (GABA) at 50 μg/ml and porcine growth hormone (GH) at 0.025 IU/ml were tested to see whether these chemicals would reduce the stress experienced by euryhaline rotifers Brachionus plicatilis species complex (L-, S- and SS-morphotypes) during low temperature (4–12°C) storage. Rotifers cultured at 25°C were transferred to 4–12°C for 10–30 days and transferred back to 25°C for recovery. GABA or GH were added to the rotifers at three different time points: 6 h before transfer from 25°C to low temperature (6h−), on day 7 after preservation at low temperature (7d+) and on the first day of recovery. For L-type rotifers, the GH treatment before the transfer to 4°C for 30 days was effective for better survival, while the GABA treatment was most effective for the S-type preserved at 10°C for 14 days. For the SS-type, the chemical treatments were not effective when the rotifers were preserved at 12°C for 14 days. After low temperature preservation, GABA treatments with the S- and SS-type rotifers just after their transfer to 25°C induced a relatively faster recovery of the rotifer population.     

Metabolic measurements and parameter estimations for bioenergetics modelling of Pacific Chub Mackerel Scomber japonicus

As a crucial step in developing a bioenergetics model for Pacific Chub Mackerel Scomber japonicus (hereafter chub mackerel), parameters related to metabolism, the largest dissipation term in bioenergetics modelling, were estimated. Swimming energetics and metabolic data for nine chub mackerel were collected at 14°C, a low temperature within the typical thermal range of this species, using variable‐speed swim‐tunnel respirometry. These new data were combined with previous speed‐dependent metabolic data at 18 and 24°C and single‐speed (1 fork length per second: FL/s) metabolic data at 15 and 20°C to estimate respiration parameters for model development. Based on the combined data, the optimal swimming speed (the swimming speed with the minimum cost of transport, U_opt) was 42.5 cm/s (1.5–3.0 FL/s or 2.1 ± 0.4 FL/s) and showed no significant dependence on temperature or fish size. The daily mass‐specific oxygen consumption rate (R, g O₂ g fish^?1 day^?1) was expressed as a function of fish mass (W), temperature (T) and swimming speed (U): R = 0.0103W^?0.490 e^(0.0457T) e^(0.0235U). Compared to other small pelagic fishes such as Pacific Herring Clupea harengus pallasii, Pacific Sardine Sardinops sagax and various anchovy species, chub mackerel respiration showed a lower dependence on fish mass, temperature and swimming speed, suggesting a greater swimming ability and lower sensitivity to environmental temperature variation.     

Induction of triploidy in Melicertus kerathurus (Forskal, 1775) with temperature shock

Triploidy in fertilized eggs of Melicertus kerathurus was induced by cold (8, 10, 12°C) and heat (34, 36, 38°C) shock for different duration times (2, 4 and 8 min) after 10 min of post spawning. The best individual treatment produced 64.5% triploid nauplii in cold shock application at a temperature of 10°C for a duration of 8 min. Temperature did not have significant effect (P > 0.05) on triploid rate but duration time had a significant effect (P < 0.05) for individual cold or heat shock. This study demonstrates that because of a wide variety of effective parameters, it is essential to optimize shock conditions for each species strain at each location.     

Temperature and fatigue effect on the maximum swimming speed of jack mackerel Trachurus japonicus

Swimming performance of jack mackerel Trachurus japonicus (18.2 ± 0.8 cm fork length (FL), n = 185) was examined in a flume tank by measuring the stride length at low and high tail beat frequencies with electromyogram monitoring and a muscle twitch experiment. Stride length was analyzed by monitoring the tail beat frequency according to the swimming speed at different temperatures of 10, 15 and 22 °C. In the electromyographic observations, the initiation of ordinary muscle activity occurred between 71.4 and 99.6 cm/s, that is 3.7 to 5.3 FL/s, when the tail beat frequency was over 6 Hz. The swimming speeds increased rectilinearly with the tail beat frequency at each water temperature both for the low and high tail beat frequency. Lower stride length was observed at the lowest temperature (10 °C) tested. The forced swimming exercise significantly affected the muscle contraction time to become longer than the control fish, which indicated a reduction of the maximum swimming speed performance.     

Effects of temperature and fatigue on the metabolism and swimming capacity of juvenile Chinese sturgeon (<Emphasis Type="Italic">Acipenser sinensis</Emphasis>)

Chinese sturgeon (Acipenser sinensis) is a critically endangered species. A flume-type respirometer, with video, was used to conduct two consecutive stepped velocity tests at 10, 15, 20, and 25 °C. Extent of recovery was measured after the 60-min recovery period between trials, and the recovery ratio for critical swimming speed (U _crit) averaged 91.88% across temperatures. Temperature (T) effects were determined by comparing U _crit, oxygen consumption rate (MO ₂), and tail beat frequency (TBF) for each temperature. Results from the two trials were compared to determine the effect of exercise. The U _crit occurring at 15 °C in both trials was significantly higher than that at 10 and 25 °C (p < 0.05). The U _crit was plotted as a function of T and curve-fitting allowed calculation of the optimal swimming temperature 3.28 BL/s at 15.96 °C (trial 1) and 2.98 BL/s at 15.85 °C (trial 2). In trial 1, MO ₂ increased rapidly with U, but then declined sharply as swimming speed approached U _crit. In trial 2, MO ₂ increased more slowly, but continuously, to U _crit. TBF was directly proportional to U and the slope (dTBF/dU) for trial 2 was significantly lower than that for trial 1. The inverse slope (tail beats per body length, TB/BL) is a measure of swimming efficiency and the significant difference in slopes implies that the exercise training provided by trial 1 led to a significant increase in swimming efficiency in trial 2.     

Developmental temperature stress and parental identity shape offspring burst swimming performance in sockeye salmon (Oncorhynchus nerka)

Abstract – The persistent effects of embryonic temperature stress and individual parentage on fry swimming performance were examined in a cross‐fertilisation experiment using sockeye salmon (Oncorhynchus nerka). A fixed‐velocity test of burst swimming was used to assess the endurance capacity and behavioural performance of individual fry from 10 offspring families incubated at 12, 14 or 16 °C to hatch and then reared through yolk absorption and exogenous feeding stages in a common posthatch environment (average 6.9 °C). Fry burst swim time (BST) was influenced by an interaction between incubation temperature and family identity. Average BST was longer for fry from the 12 °C prehatch treatment compared to 14 and 16 °C, although differences were largely attributable to temperature effects on average fry size. Behavioural observations revealed that fish incubated at 16 °C performed more poorly, having a larger proportion of individuals that required stimulation to swim, fatigued more frequently or were classified as ‘nonswimmers’. Within all three incubation temperature treatments, mean BST varied significantly among offspring families, independent of fry mass and length. An interesting relationship was observed within the 16 °C treatment, whereby families with higher survivorship were characterised with lower mean BSTs. Collectively, these findings demonstrate that exposure to high temperatures in early sockeye salmon development can result in persistent, parentally mediated effects on fry performance. As such, these results provide important insight into how elevated temperature events during egg incubation may affect early life history selection processes and survival in stages beyond when the stressor is experienced.     

The effect of temperature on the energy budget of the Manila clam, <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>

In this study, the energy budget of the Manila clam, Ruditapes philippinarum, was evaluated after one-week acclimation periods at 5, 10, 15, 20, and 25°C. Small clams (151 ± 12 mg DW) and large clams (353 ± 16 mg DW) were fed with the microalgae, Isochrysis galbana. Filtration rate, ingestion rate, assimilation efficiency, oxygen-consumption rate, and ammonia excretion rate were measured. Both filtration rate and ingestion rate of small and large clams were found to be related to temperature. The highest Q ₁₀ values were measured in the range 15–20°C for both small and large clams. Assimilation efficiency of both small and large clams was not significantly influenced by temperature, although the maximum mean values were detected at 20°C. Oxygen consumption rate and ammonia excretion rate of small and large clams were found to be related directly to temperature over the entire range, with a maximum being detected at 25°C. The highest Q ₁₀ value was estimated in the range 10–15°C with regard to oxygen consumption rate, and in the range of 15–20°C with regard to ammonia excretion rate. Scope for growth (SFG) was positive at all temperatures, achieving a maximum value at 20°C in both small and large clams, primarily as a consequence of the enhanced ingestion rate which offset the concomitant elevation in the metabolic rate. In this study we have estimated the thermal optimum for this species at 20°C.     

Cross‐effects of dietary probiotic supplementation and rearing temperature on growth performance,digestive enzyme activities,cumulative mortality and innate immune response in seabass (Dicentrarchus labrax)

Probiotic influence on fish immune response and digestive capacity is extensively discussed in aquaculture. In this experiment, a feeding trial was carried out for 100 days to evaluate the cross‐effects of probiotic supplementation and rearing temperature (17, 20 and 23°C) in juvenile seabass (Dicentrarchus labrax). The experimental diet was supplemented with a commercial probiotic blend (Biomin AquaStar Growout) at 3 g/kg diet (5.23 × 10⁸ CFU/kg diet), and tested against a non‐supplemented diet (control). Growth performance and innate immune responses were analysed at 70 and 100 days of feeding, whereas digestive enzyme activities were determined at 100 days of feeding. At the end of the feeding trial, fish were subjected to a handling stress and cumulative mortality was recorded. Digestive enzyme activities were influenced by temperature, with α‐amylase and lipase activities peaking at the higher temperature (23°C) and trypsin at the lower temperature (17°C). Immune parameters showed a significant temperature versus feeding duration effect, with complement system (ACH50) and peroxidase peaking at 70 and 100 days of feeding, respectively. Poststress cumulative mortality was higher at the lowest temperature (17°C), especially in fish fed the control diet. In conclusion, water temperature was the main variable affecting the studied parameters, whereas the dietary probiotic supplementation had influence on the chymotrypsin activity and survival rate in seabass reared at 17°C.     

Swimming angle and target strength of larval Japanese anchovy (<Emphasis Type="Italic">Engraulis japonicus</Emphasis>)

The swimming angle of larval Japanese anchovy (Engraulis japonicus) was measured in a tank, and target strength (TS) was calculated using a theoretical scattering model. The mean swimming angle was 12.8° (SD ±22.1). Increased speeds of flow led to increased mean swimming angles. The mean swimming angle at flow of 5 cm s⁻¹ was higher than at other speeds. TS values were estimated using a distorted-wave Born approximation model for two cases. Average values were 1–3 cm s⁻¹ (11.5° ± 22.1) and 5 cm s⁻¹ (16.6° ± 21.7) for cases 1 and 2, respectively. For case 1, TS ranged from −92.0 to −74.7 dB with a mean of −79.4 dB at 120 kHz. For case 2, TS ranged from −92.2 to −75.2 dB with a mean of −79.9 dB. The mean TS in case 2 was lower than that in case 1, with the maximum difference being 1.0 dB at 120 kHz (standard length 22.0 mm). However, there were no significant differences between the regression lines of cases 1 and 2. Thus, changes in flow speed altered the swimming angle of larval Japanese anchovy, but had little influence on TS.     

Effect of temperature on muscle lactate metabolic recovery in sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>, L.) juveniles exposed to exhaustive exercise

Muscle lactate metabolic recovery in sea bass juveniles was studied in respect to the water temperature. The fish used in this study were cultured with the semi-extensive mesocosm method, and the water temperatures were 15 and 20°C. Fish were led to exhaustion by exercising in a swimming channel, and the muscle lactate levels were measured seven times before and after exercise. The results showed that muscle lactate concentration rises during exercise until it reaches a maximum (exhaustion point), and then it keeps falling during the recovery time. Also, fish exercised at 20°C exhibited higher lactate values at the exhaustion point and faster decomposition rates during recovery.     

Establishment,characterization of a new cell line from heart of half smooth tongue sole (<Emphasis Type="Italic">Cynoglossus semilaevis</Emphasis>)

A new cell line was established from the heart of a cultured marine fish, half smooth tongue sole (Cynoglossus semilaevis), designated as CSH (Cynoglossus semilaevis heart cell line). The CSH cells grow over 400 days in minimum essential medium (MEM) supplemented with 10% fetal bovine serum (FBS) and 2 ng/ml basic fibroblast growth factor (bFGF). The suitable temperature for the cell growth was 24–30°C with the optimum growth at 24°C and a reduced growth at 12 and 30°C. FBS and bFGF concentration were the two important components for CSH cells proliferation. Twenty percent FBS in the medium was found to be the optimum concentration and bFGF promoted the growth of CSH cells. The double time of the cells at 24°C was determined to 73.39 h. Chromosome analysis revealed that 44% of the cells maintained a normal diploid chromosome number (2n = 42) in the CSH cells at Passage 58. The fluorescent signals were observed in CSH after the cells were transfected with green fluorescent protein (GFP) reporter plasmids. CSH cells showed the cytopathic effect (CPE) after infection with lymphosystis disease virus (LCDV). Moreover, the LCDV particles can be observed in the cytoplasm of virus-infected cells by electron microscopy, and a segment of MCP gene for major capsid protein of LCDV was found by PCR amplification DNA of virus-infected cells.     

Effects of rhythmic temperature change on the growth,body composition and energy budget of hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀)

Effects of rhythmic temperature change on the growth, body composition and energy budget of hybrid grouper (Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀) were investigated. Nine groups of fish received repeating cycles of low‐temperature manipulation (22°C) for 1, 2 and 4 days followed by recovery temperature (28°C) for (3, 7 and 11 days), (6, 14 and 22 days) and (12, 28 and 44 days) respectively, designated as L1R3, L1R7, L1R11, L2R6, L2R14, L2R22, L4R12, L4R28 and L4R44 respectively. In the control group (C), fish were reared at 28°C throughout the whole experiment. After 96‐day feeding trail, the final weight, relative weight gain rate, specific growth rate, food conversion efficiency and apparent digestibility coefficient of fish in L4R28 were significantly higher than those of control (p < .05). The crude protein contents of fish in L2R14, L2R22, L4R12, L4R28 and L4R44 were significantly higher compared to the control (p < .05). According to energy budget, fish in L4R28 exhibited significantly higher proportion of food energy assimilated into growth and lower proportion consumed for excretion than the control fish (p < .05). These results indicated the occurrence of complete or over growth compensation in hybrid grouper, and the use of repeated cycles of low temperature (22°C) for 4 days followed by recovery temperature (28°C) for 28 days could obtain enhanced growth, that is overcompensation, with improved apparent digestibility coefficient, food conversion efficiency and energetic efficiency into growth. This technique would be more practically applicable in indoor culture for this species.     

Pre-spawning water temperature affects sperm respiration and reactivation parameters in male carps

Concentration, ability to motility, motility during the second activation (reactivation), and endogenous respiration were studied in sperm from two experimental groups of carp males. Group 1 was maintained for 7 days at 15°C (cold water (CW) group), whereas the second group was subjected to a temperature of 20°C (warm water (WW) group) before sperm sampling. Reactivation were achieved after incubation of firstly activated sperm in media with osmotic pressure adjusted up to 300 mOsm*kg⁻¹ by increasing K⁺ concentration. Statistically significant reduction of spermatozoa concentration in CW samples versus WW (from 46.0 ± 12.5 (15°C) to 59.3 ± 7 10⁹ (20°C) spermatozoa /ml) have been observed. The sperm of the CW group required a significantly longer incubation time (37 min) under isotonic conditions to achieve a maximum percentage of potent motility at repeated activation than the WW group (23 min). After activation of sperm motility, an increase of respiration rate up to maximum level has been found, this level remained the same under condition of recovering the potential to repeated activation. During the sperm movement respiration rate, in CW group (6.1 nmolO₂/min/10⁹spermatozoa) and WW (3.9 nmolO₂/min/10⁹spermatozoa), was significant higher compared to nonactivated sperm (2.4 nmolO₂/min/10⁹spermatozoa for CW and 1.1 nmolO₂ /min/10⁹spermatozoa for WW). And keeping males for 7 days at 15°C increase the respiration rate of sperm.     

Effect of temperature on swimming performance of juvenile Schizothorax prenanti

The migration of Schizothorax prenanti, an ecologically important and commercially valuable species, is impeded by dams. Effective fishways would contribute to conservation of wild populations, and swimming performance data are necessary for fishway design. The swimming performance of S. prenanti was investigated at four temperatures (15, 19, 23, 27 °C), and numerical models were used to characterize the effect of temperature on swimming performance. As temperature increases, critical swimming speed (U _crit) increases from 15 to 23 °C and then decreases significantly. The highest U _crit (7.71 BL/s) occurs at 24 °C, as estimated by interpolation. Swimming efficiency was similar from 19 to 23 °C, but decreases significantly at 27 °C. The temperature range 15–23 °C is suitable for S. prenanti. However, the excess post-exercise oxygen consumption values of Q ₁₀ for the four temperature increments indicate that 19–23 °C is the optimal range for swimming performance. Maximum tail beat amplitude increased >25 % (0.35–0.45 BL) over the temperature range considered, but variation of tail beat frequency was erratic. White muscle fiber begins to contribute to swimming at swimming speeds ~40 % U _crit at the lower three temperatures, but increases to almost 60 % at 27 °C, and the contribution is relatively small. The results of this investigation advance the knowledge of fish metabolism while swimming provides data critical for fishway design.     

Effects of temperature and salinity on oxygen consumption and ammonia excretion of juvenile miiuy croaker, <Emphasis Type="Italic">Miichthys miiuy</Emphasis> (Basilewsky)

The metabolic responses of the juvenile Miichthys miiuy in terms of oxygen consumption and ammonia excretion to changes in temperature (6–25°C) and salinity (16–31 ppt) were investigated. At a constant salinity of 26 ppt, the oxygen consumption rate (OCR) of the fish increased with an increase in temperature and ranged between 133.38 and 594.96 μg O₂ h⁻¹ g⁻¹ DW. The effect of temperature on OCR was significant (P < 0.01). Q₁₀ coefficients were 6.80, 1.41, 1.29 and 2.36 at temperatures of 6–10, 10–15, 15–20 and 20–25°C, respectively, suggesting that the juveniles of M. miiuy will be well adapted to the field temperature in the summer, but not in the winter. The ammonium excretion rates (AER) of the fish were also affected significantly by temperature (P < 0.01). The O:N ratio at temperatures of 6, 10, 15 and 20°C ranged from 13.12 to 20.91, which was indicative of a protein-dominated metabolism, whereas the O:N at a temperature of 25°C was 51.37, suggesting that protein-lipids were used as an energy substrate. At a constant temperature of 15°C, the OCRs of the fish ranged between 334.14 (at 31 ppt) and 409.68 (at 16 ppt) μg O₂ h⁻¹ g⁻¹ DW. No significant differences were observed in the OCR and AER of the juveniles between salinities of 26 and 31 ppt (P > 0.05). The OCR and AER at 16 ppt were, however, significantly higher than those at 26 and 31 ppt (P < 0.05), indicating salinity lower than 16 ppt is presumably stressful to M. miiuy juveniles.