The role of glycogen phosphorylase in the regulation of glycogenolysis by insulin and glucagon in isolated eel (Anguilla rostrata) hepatocytes

The effects of porcine, scombroid, and salmon insulins, and bovine and anglerfish glucagons on glycogen depletion and glycogen phosphorylase (GPase) activities were examined in freshly isolated American eel (Anguilla rostrata) hepatocytes. Eel liver GPase in crude homogenates was activated (increase in % GPase a) by phosphorylating conditions and was rapidly inactivated (less than 1 h) when a phosphatase inhibitor (fluoride) was absent. Caffeine inhibits, and AMP activates, the b form of GPase consistent with their effects on rat liver GPase. Both mammalian and fish glucagons increased glucose production in eel hepatocytes, but had more ambiguous effects on glycogen levels and GPase activities. The magnitude of bovine glucagon effects were dependent on the initial glycogen content of the cells; only at glycogen concentrations less than approximately 70 μmoles.g⁻¹ did glucagon significantly increase % GPase a. Anglerfish glucagon significantly increased cyclic AMP (cAMP) concentrations by 90% at 10⁻⁷ M, but had no effects at 10⁻⁹ M and 10⁻⁸ M. Scombroid and salmon insulins maintained hepatocyte glycogen concentrations and decreased glucose production, with these effects more pronounced at low (10⁻⁹ to 10⁻⁸ M) rather than high (10⁻⁷ M) hormone concentrations. Porcine and salmon insulins decreased total GPase and % GPase a activities, and salmon insulin decreased CAMP levels, but only at 10⁻⁸ M (by 44%). Glycogen is, therefore, depleted by glucagon and maintained by insulin in freshly isolated American eel hepatocytes, and these changes are accomplished, at least in part, by changes in the activities of GPase. Changes in cAMP do not explain all of the observed hormone effects.     

Changes in plasma glucagon and insulin associated with fasting in sea bass (Dicentrarchus labrax)

Juvenile sea bass (Dicentrarchus labrax) were fasted for 22 days and changes in plasma insulin, glucagon and glucose levels, as well as glycogen and protein content in liver and muscle were analyzed. Glucagon increased initially on the 4th day of fasting. The glucagon/insulin ratio (G/I) increased from a value of 0.11±0.02 (24h of fasting) to 0.21±0.05 (4th day of fasting). Thereafter, both glucagon and insulin levels decreased and remained at low concentrations until the 22nd day of fasting. Plasma glucose levels fell at the beginning of fasting, stabilized between the 4th and 8th day, and gradually declined during the rest of the experiment. There was a body weight loss of 15% and a significant decrease in both the hepatosomatic index and mesenteric fat. The decrease in the percentage of muscle proteins was not significant, while liver glycogen content showed a sharp decline.     

Are cell redox or lactate dehydrogenase kinetics responsible for the absence of gluconeogenesis from lactate in sea raven,hepatocytes?

Previous studies have reported very low rates of gluconeogenesis from lactate in sea raven (Hemitripterus americanus) hepatocytes compared to other teleosts studied. This study examines whether hepatic cell redox or lactate dehydrogenase (LDH) characteristics may explain this observation. Sea raven hepatic optimal LDH activities (pyruvate reductase direction) were more than 40 times less compared with rainbow trout liver values (40 vs 1914 μmol·min⁻¹·g⁻¹ protein). The Km(lactate) was 9.24 and 0.86 mM for sea raven and trout hepatic LDH, but the Km(pyruvate) was similar between the two species (0.11 and 0.21 mM, respectively). These results suggested that sea raven liver LDH did not favour lactate use and was more indicative of the mammalian M-isozyme. Gel electrophoresis showed a predominant intermediate isozyme, with a small amount of the M-type LDH. Phosphoenolpyruvate carboxykinase (PEPCK) was localized to the mitochondrial compartment, while there was no apparent mitochondrial glutamate-oxaloacetate transaminase (GOT) activity. No in vitro lactate flux to glucose was found in untreated, 10 mM ethanol-treated, or 3 mM NH₄Cl-treated sea raven hepatocytes, although CO₂ production from lactate was decreased by ethanol and increased by NH₄Cl. These results provide evidence that cell redox does not limit gluconeogenesis from lactate, while low activities and the kinetic characteristics of LDH may partially explain the low lactate gluconeogenesis reported in sea raven hepatocytes. To whom correspondence should be addressed at University of Ottawa.     

Cortisol and hematological response in Brazilian codling, Urophycis brasiliensis (Pisces, Phycidae) subjected to anesthetic treatment

The effects of benzocaine anesthesia on hematological parameters (erythrocyte and platelet number, hemoglobin concentration and hematocrit), plasma electrolytes (Na⁺, K⁺ and Cl⁻), cortisol, glucose and cholesterol levels in Brazilian codling (Urophycis brasilensis) exposed to a benzocaine bath solution were investigated. Cortisol and glucose levels 1 h after capture from the wild and on days 7 and 14 during the acclimatization period (20 days) were also determined. During the second week, cortisol levels reached to basal values (9 ng ml⁻¹). The use of benzocaine causes a significant increase in the erythrocyte number, in the concentration of hemoglobin and sodium and a decrease in chloride. Plasma cortisol and cholesterol levels were higher in fish exposed to the anesthetic, and glucose levels decreased significantly comparing with the control group, showing strong fluctuations between individuals in all the cases. These results show that the use of benzocaine causes an acute stress response that could be reverted quickly and it has to be considered during the evaluation of stress in fish.     

Live microbial feed supplement in aquaculture for improvement of stress tolerance

Two bacterial strains, Lactobacillus fructivorans, isolated from sea bream (Sparus aurata) gut, and Lactobacillus plantarum, isolated from human faeces, were administered simultaneously, during sea bream development, using Brachionus plicatilis and/or Artemia salina as vectors. The probiotic treatment significantly affected gut colonization. To test the probiotic influence on stress responsiveness, sea bream fry, 47 days post-hatching (p.h.), were subjected to pH stress (from 8.6 to 6.3) and cumulative mortality, cortisol levels and HSP70 gene expression were analysed. Cortisol was selected, since under stress conditions its level increases. HSP70 was selected with consideration of its wide involvement in response to a great number of injuries, and because it protects cells probably by binding and refolding damaged proteins. The results obtained indicated that the administration of probiotic to sea bream fry induced higher HSP70 levels, indicating a greater potentiality to respond to the harmful conditions possibly present in fish farms. This hypothesis is supported by the fact that the levels of cortisol found were significantly lower (P < 0.05) in both groups under probiotic treatment. When pH was used as a stressor, it induced a higher cumulative mortality in the control; the mortality was found to be significantly lower in both treated groups. Interestingly, a significant increase (P < 0.05) in HSP70 gene expression was observed in all stressed groups. These results suggest an improvement in tolerance to acute stress of fry fed with probiotics.     

Glycogenolytic action of glucagon-family peptides and epinephrine on catfish hepatocytes

Glycogenolytic effects of salmon and mammalian glucagons, salmon glucagon-like peptide (GLP) and epinephrine were studied on liver cells isolated from catfish (Ictalurus melas). In spring and summer, salmo-glucagon (3×10^–10 to 3×10^–8 M) was more effective than its mammalian counterpart in the stimulation of glucose release and cAMP synthesis in hepatocytes. GLP was less potent as compared to both glucagons. -amylase activity was not affected by the treatment with either glucagon-family peptides or epinephrine.The comparison of the glycogenolytic effects of salmon glucagon to those of epinephrine reveals a greater potency of the latter hormone in the stimulation of cAMP synthesis, glycogen-phosphorylase activity and glucose release. Glycogen content in the liver cells was equally depleted after treatment with both of the two hormones.     

Carbohydrate metabolism and hepatic zonation in the Atlantic hagfish,Myxine glutinosa liver: effects of hormones

Viable Atlantic hagfish (Myxine glutinosa) hepatocytes were isolated from combined or separated large and small lobes and carbohydrate metabolism was studied. Cells had low levels of glycogen (16–30 μmol·g⁻¹), and low rates of total glucose production (TGP; 0–480 nmol·h⁻¹·g⁻¹ cells). Lactate flux to glucose (5.5 nmol·h⁻¹·g⁻¹) and CO₂ (76 nmol·h⁻¹·g⁻¹) was lower than reported values for teleosts, with a low percentage (30%) of the lactate carbon reaching glucose. Insulin significantly increased total glucose production and gluconeogenesis and decreased 6-phosphofructo 1-kinase (PFK-1) activities and glucose oxidation, while glucagon was without effect on any parameter studied. Forskolin significantly increased TGP. Epinephrine (Epi), norepinephrine (NEpi), isoproterenol (Iso), and phenylephrine (Phe) all decreased CO₂ production from lactate; propanolol blocked the effects of Epi, NEpi, and Iso. The large lobe, accounting for 65% of total liver mass, had a higher glycogen content and higher CO₂ production from lactate compared to the small lobe. Furthermore, enzyme activities in the large lobe were greater than in the small lobe, with the exception of glycogen phosphorylase (GPase) which exhibited smaller %a values in the large lobe. These data indicate the presence of a hormonally-responsive carbohydrate metabolism in hagfish hepatocytes, which is qualitatively and quantitatively different between the two liver lobes.     

Fate of plasma glucose in tissues of brown trout in vivo: effects of fasting and glucose loading

We report the fate of glucose, both as a source of energy and as a temporary store, in the tissues of brown trout (Salmo trutta) in control, fasted and glucose-loaded fish. Tissue glucose utilization (³H-2-deoxyglucose phosphorylation) and storage (conversion of ¹⁴C-glucose into glycogen, protein, and lipid) were measured in immature brown trout, and the oxidation rate was calculated as glucose utilization minus storage and ¹⁴C-ionic metabolites remaining in the tissue. The glucose utilization rate is tissue-specific, the highest values being found in spleen, kidney, hindgut, brain, and gill. All these tissues also showed a highly active glycolytic pathway. The lowest utilization indices were observed in white and red muscles, skin, stomach and caeca, which also presented the largest proportion of glucose converted into stores (mainly protein and glycogen). Fasting reduced the glucose disappearance rate by 24%, although there were no significant variations in glucose utilization indices or distribution profile. After a glucose load, plasma glucose and insulin levels rose and the rates of glucose utilization, storage, and oxidation also increased in all tissues (from 1.5- to 4-fold). The relative importance of each tissue in glucose disposal was similar to that in normoglycaemia. In liver, only glucose storage was measured reliably; the conversion of glucose to glycogen was higher than in other tissues, and rose markedly (35-fold) in glucose-loaded fish. In most tissues glucose flux into lipids, glycogen and protein increased. The distribution of glucose may not be a merely substrate-mediated process because fasting in glucose-loaded fish caused lower tissue glucose utilization, particularly in gut, red muscle and gills. Conversion of glucose to tissue stores was reduced, lipids being the most affected.     

Cortisol-induced changes in oxygen consumption and ionic regulation in coastal cutthroat trout (Oncorhynchus clarki clarki) parr

The influence of cortisol on oxygen consumption and osmoregulatory variables was examined in coastal cutthroat trout (Oncorhynchus clarki clarki) parr kept in fresh water (FW) and transferred to seawater (SW). Intraperitoneal implants containing cortisol (50 g g^–1) in vegetable oil resulted in elevated plasma cortisol titres similar to those observed in fish following a 24h SW exposure. Cortisol treatment significantly increased the oxygen consumption and plasma glucose levels of trout in FW, consistent with the glucocorticoid role of cortisol. Cortisol treatment did not cause any changes in plasma ion concentrations or gill Na⁺,K⁺-ATPase activity in FW after 10 days. Cortisol-implanted fish exposed to SW for 24h showed slightly improved ion regulatory ability compare to non-implanted controls. The results of this study suggest that during SW transfer in juvenile salmonids, increases in cortisol may act as both a mineralocorticoid and a glucocorticoid, depending on the developmental state of the fish (e.g., smolt versus parr). Furthermore, the relative energetic costs of osmoregulation and that of the stress associated SW transfer cannot be discerned using whole-animal oxygen consumption rates.     

Haematological, biochemical and immunological parameters as stress indicators in Dicentrarchus labrax and Sparus aurata farmed in off-shore cages

In 2000–2001, an investigation was performed in two Sicilian mariculture sites (Pachino and Castellammare) to monitor physiological and biochemical parameters in sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) specimens farmed in off-shore sea cages. Plasma cortisol and glucose levels, tissue lactate concentration, haematocrit and haemoglobin content, lysozyme, haemolytic and haemagglutinating activities were determined. During the experiment, an increase in tissue lactate and plasma cortisol levels and a reduction in haemolytic and haemagglutinating titers, were recorded. Changes occurring in these haematological, immunological and biochemical values suggest that these parameters can be useful indicators in assessing the condition of chronic stress induced by mariculture operations.     

Effect of handling and fish size on secondary changes in carbohydrate metabolism in Atlantic salmon, Salmo salar L.

Two size groups (0.5 and 3 kg) of Atlantic salmon, Salmo salar L., were stressed by netting and transport from sea cages into land-based tanks. Handling lasted for 1 h. Before onset of stress, basal concentrations of haematocrit and haemoglobin, plasma cortisol and glucose, and liver and muscle glycogen were measured. All levels were within ranges reported for salmon. After handling and at chosen time intervals during recovery, samples were taken to judge the impact of handling and whether secondary changes in carbohydrate metabolism were related of fish size. A low cortisol peak indicated a mild stress reaction after handling independent to fish size. Plasma glucose peaked as cortisol declined, and returned to basal levels within 48 h. Liver glycogen seemed to be the main source of plasma glucose. No changes were measured in muscle glycogen concentrations. The results indicate a high tolerance to handling stress in Atlantic salmon independent of fish size.     

船载振动胁迫对斑石鲷影响实验研究

为了探索鱼类在船载振动条件下的应激响应和适应性,为深远海大型养殖平台养殖工艺设计与模式构建提供基础数据和理论依据,利用机械振动台模拟船载工况,研究不同振动频率和时间条件下斑石鲷(Oplegnathus punctatus)的血液和生化指标变化情况。结果表明:振动时间5 min,10 Hz组和50 Hz组的斑石鲷各方面指标均与对照组无显著性差异,30 Hz组的血清葡萄糖显著降低,皮质醇和肾上腺素指标显著升高,肌糖原和肝糖原无显著差异;振动时间60 min,各实验组斑石鲷的血清葡萄糖指标均显著降低,皮质醇和肾上腺素指标显著升高,但对肌糖原和肝糖原指标无显著影响;水质变化情况显示,振动60 min后水体内溶氧浓度和氨氮浓度指标有所上升,水温、盐度、p H等无明显变化。研究表明,低频振动对鱼类的影响主要是通过产生水流变化进而被侧线器官感受到,引起斑石鲷脑神经兴奋,产生应激。短时振动对斑石鲷不会造成较大影响,而长时间振动会引起斑石鲷一定程度的应激反应。     

Stress and metabolic indicators in a relatively high (European sea bass,Dicentrarchus labrax) and a low (meagre,Argyrosomus regius) cortisol responsive species,in different water temperatures

The aim of this study was to examine species‐specific differences in pre‐ and post‐stress concentrations of haematological, metabolic and hormonal parameters in two Mediterranean fish species, one with relatively high (European sea bass, Dicentrarchus labrax) and the other with low (meagre, Argyrosomus regius) basal and post‐stress blood cortisol concentrations, in relation to different water temperatures. Fish were reared in net‐pen sea cages and exposed to an identical acute stressor (crowding and chasing with a net for 5 min) in three different periods of the year. Results indicated that inter‐specific differences occurred in most of the examined parameters. In addition, within each species, differences between sampling periods existed in plasma cortisol, glucose, osmolarity, blood pH and muscle glycogen concentration. Glucose, lactate and osmotic pressure showed a constant pattern of change, with maxima at half an hour post stress in both species, while cortisol, and blood and muscle pH, were significantly altered only in E. sea bass. No alterations were observed in liver and muscle glycogen concentrations in E. sea bass, while a significant reduction was evident only in the coldest temperature in meagre. It is concluded that there are important species‐specific differences in the magnitude of hormonal and metabolic response to acute stress and that both basal and post‐stress blood cortisol concentrations are affected by the sampling period.     

Consistency of stress response to repeated handling in the gilthead sea bream Sparus aurata Linnaeus, 1758

Gilthead sea bream Sparus aurata Linnaeus, 1758 were subjected to repeated stresses, namely confinement and handling once a month for 5 consecutive months. Plasma cortisol concentration was determined as a primary stress response, and plasma glucose and osmolality, serum agglutination and growth rate were analysed as indicators of the secondary and tertiary effects of stress. The results of the mean values after the five trials showed that most indicators followed a consistent pattern with time. Cortisol and growth rate were positively correlated, and cortisol and osmolality were negatively correlated after stress. Analysis of the individual responses throughout all 5 months showed that 6–20% of the fish displayed a consistently high or low response depending on the parameter analysed.     

Cortisol stimulates intestinal fluid uptake in Atlantic salmon (Salmo salar) in the post-smolt stage

The fluid uptake rate of the posterior intestine of salmonids increases during the parr-smolt transformation. Intestinal fluid uptake in post-smolt Atlantic salmon was investigated after treatment with cortisol and growth hormone (GH), alone or together. Two replicate experiments were conducted in August 1991 and August 1992. Cortisol was emulsified in vegetable shortening and vegetable oil (1:1) and implanted into the peritoneal cavity. GH was administered as intraperitoneal injections in a saline vehicle on days 0 and 2. On days 5 and 6, plasma cortisol levels, gill Na⁺,K⁺-ATPase activity, andin vitro measurements of fluid transport rate (J_v) across the posterior intestine were measured. Implants of cortisol elevated the plasma cortisol levels within a physiological range, and resulted in elevated gill Na⁺,K⁺-ATPase activity, as expected. The fluid uptake rate across the posterior intestine was roughly doubled by cortisol treatment. GH treatment did not affect intestinal fluid transport, gill Na⁺,K⁺-ATPase activity, or plasma cortisol concentrations. The seawater-adapting increase in the rate of fluid uptake by the posterior intestine of smolting salmon is probably stimulated by elevated plasma cortisol concentrations.     

Water quality and physiological response of F1 hybrid seabream (Pagrus major♀ × Acanthopagrus schlegelii♂) to transport stress at different densities

Hybrid seabream (Pagrus major♀ × Acanthopagrus schlegelii♂) grow quickly, with retarded gonadal growth and enhanced muscle nutritional composition. This F₁ hybrid seabream is a new marine aquaculture fish in China. However, the response of hybrid seabream to transport is severe, which seriously restricts its promotion and development. Water quality and the physiological response of hybrid sea bream were studied at three fish transport densities (5, 10 and 20 g/L) during 8 hr of transport in a light van (60 km hr^?1 and 25°C water temperature). We found that total ammonia–nitrogen and nitrite–nitrogen levels in the water of the highest density group increased sharply after 4 and 8 hr of transport. Cumulative survival of the fish in the 10 and 20 g/L groups (86.7% and 75% respectively) was significantly lower than in the 5 g/L group (100%) after 8 hr of transport (p < .05). Serum cortisol and lactate levels were significantly higher after transport than pre‐stress levels, whereas the glucose level decreased significantly (p < .05). Hepatic triglyceride and glycogen levels and superoxide dismutase and catalase activities were significantly lower in the 20 g/L group than in the 5 g/L group (p < .05). The results show that high‐density transport increased ammonia–nitrogen and nitrite–nitrogen levels in the water as well as cortisol secretion and anaerobic metabolism in the F₁ hybrid seabream, suggesting that total cholesterol and glycogen may be used to supply the energy demand and increased oxidative stress. These results will help to optimize the transport conditions for cultured hybrid seabream.     

Physiological responses associated with capture and crowding stress in matrinxãBrycon cephalus (Gunther, 1869)

The dynamics of plasma cortisol, blood glucose, plasma chloride and liver glycogen were investigated in matrinxã (Brycon cephalus) submitted to capture and various periods of crowding. A total of 400 fish (700±22 g weight) were distributed in four ponds divided into four 50‐m² squares (25 fish/square, 350 g L^?1), where they were acclimated for 30 days. On the sampling day, after 24 h without food, all fish from three squares were transferred to the fourth square. Six fish were sampled before the procedure (control group, zero time) and 1, 3, 6 and 24 h after the capture and crowding. Each sampling was performed in a different pond to prevent additional stress. Fish were anaesthetized and blood and liver collected for biochemical analysis. Water temperature, pH, dissolved oxygen, alkalinity, ammonia and nitrite levels were within acceptable levels for matrinxã rearing. Slight but not significant increases were verified in plasma cortisol and blood glucose levels, as were decreases in plasma chloride and liver glycogen levels. The results suggest that matrinxã is highly tolerant to the procedures of capture and short‐term crowding.     

Effects of chronic confinement on physiological responses of juvenile gilthead sea bream, Sparus aurata L., to acute handling

Understanding how gilthead sea bream, Sparus aurata L., an important Mediterranean Sea species for aquaculture, respond physiologically to stressors commonly encountered in intensive rearing is important for effective production, as managing for stress is a major factor in maintaining healthy fish stocks. Our objective was to determine whether holding juvenile gilthead sea bream at a high density (HD), as a chronic stressor, would affect their physiological responses to a subsequent acute handling stressor. After acclimation at a low density (LD) of 6 kg m^?3 in 200‐L circular tanks containing 33–36 g L^?1 recirculating seawater at 19°C under a normal photoperiod, juvenile 37‐g gilthead sea bream were confined for 14 days at a HD of 26 kg m^?3 and then subjected to 30‐s aerial emersion in a dipnet. Plasma levels of cortisol, glucose, lactate, osmolality and chloride were determined in fish held in separate lots during LD (control) and HD confinement at 0, 1, 2, 7 and 14 days, and then after handling at 0, 1, 2, 4 and 8 h. Although plasma cortisol levels were similar in LD and HD fish groups after 14 d of confinement (15 and 23 ng mL^?1, respectively), the cortisol response in fish from the HD treatment at 1 and 2 h following acute handling (70 and 37 ng mL^?1, respectively) was only about half of that measured in the control group (139 and 102 ng mL^?1); plasma cortisol was similar in both groups by 4 and 8 h. In contrast, plasma glucose elevations in response to handling were higher at 4 and 8 h in the HD‐held fish (94 and 72 mg dL^?1, respectively) than in those from the LD treatment (59 and 51 mg dL^?1); glucose responses were similar in both groups at 1 and 2 h after handling and throughout confinement. Plasma lactate levels were higher in LD fish than in the HD group at the beginning of the experiment but were similar after 14 d confinement and responses to handling were similar (e.g. 33 and 35 mg dL^?1 at 1 h). Plasma osmolality showed increases during the first 2 h after acute handling but no differences were evident between the two density treatments at any time during confinement or posthandling. Plasma chloride levels did not change throughout the experiment. The reduced plasma cortisol response to acute handling likely resulted from negative feedback of mildly but chronically elevated circulating cortisol caused by the confinement stressor on the hypothalamic–pituitary–interrenal axis. While other post‐handling physiological changes also showed differences between treatment groups, the suppressed cortisol response in the HD‐held fish suggests a reduction in the gilthead sea bream's normal capacity to respond to an acute stressor.     

Modelling the effects of capture and sea lice [Lepeophtheirus salmonis (Krøyer)] infestation on the cortisol stress response in trout

Measuring baseline cortisol in wild salmonids is problematic because of the stress induced by most capture methods. The cortisol response to different periods of confinement stress was modelled in a laboratory population of rainbow trout [Oncorhynchus mykiss (Walbaum)]. A quadratic model was used to predict baseline (precapture) cortisol levels in these fish. A similar quadratic response pattern of cortisol was observed in wild sea trout (Salmo trutta L.). These were captured in timed sequences on four dates by seine netting in Clew Bay, west coast of Ireland. The estimated precapture cortisol for these fish indicated higher levels soon after migration to sea and a positive correlation with the level of infestation by Lepeophtheirus salmonis (Krøyer). Curvilinearity of the quadratic model was correlated with levels of lice infestation, indicating an enhanced cortisol response to confinement stress during capture when parasitic abundance was high. Estimated precapture cortisol for individual sea trout was positively correlated with numbers of lice although the linear regression had low predictive power. The method provides, for the first time, a means to estimate baseline cortisol levels in wild salmonids, and addresses one of the most difficult problems in working with wild fish. Keywords: Cortisol, trout, Lepeophtheirus salmonis (Krøyer), capture, quadratic model     

Effect of blood glucose level on acute stress response of grass carp <Emphasis Type="Italic">Ctenopharyngodon idella</Emphasis>

Stress has a considerable impact on welfare and productivity of fish, and blood glucose level of fish may be a factor modulating stress response. This study evaluated the effect of blood glucose level and handling on acute stress response of grass carp Ctenopharyngodon idella. Fish were intraperitoneally injected with glucose at 0, 0.2, 0.5, and 1.0 mg g^?1 body mass (BM) and then were exposed to handling for 5 min. Glucose injection resulted in increase of plasma glucose level and liver glycogen content and decrease of plasma lactate level. Handling resulted in increase of plasma levels of cortisol, glucose, and lactate and plasma lactic dehydrogenase (LDH) activity and decrease of liver glycogen content. At 1 h post-stress, the plasma cortisol level was lower in the stressed fish injected with glucose at 0.5 mg g^?1 BM than the stressed fish injected with glucose at 0, 0.2, and 1.0 mg g^?1 BM. No significant differences were found in the activities of phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate kinase (PK) in the liver between the stressed and unstressed fish, regardless of the dose of glucose injection. At 1 h post-stress, the liver glucose-6-phosphatase (G6Pase) activity was higher in the fish without glucose injection than in the fish injected with glucose. This study reveals that blood glucose level can affect stress response of grass carp by modulating cortisol release and glucose homeostasis through glycogen metabolism and gluconeogenesis in the liver.