Temperature affects physiological stress responses to acute confinement in sunshine bass (Morone chrysops x Morone saxatilis)

Sunshine bass (Morone chrysopsxMorone saxatilis) were subjected to a 15-min low-water confinement stressor at temperatures ranging from 5 to 30 degrees C. Physiological responses were evaluated by measuring hematocrit, and plasma chloride, glucose and cortisol. Fish acclimated to 30 degrees C had initial glucose concentrations of 3.13 mM (564 mg/L) which were significantly lower than in fish acclimated to 5 and 10 degrees C (4.32 and 4.82 mM or 779 and 868 mg/l, respectively). Fish survived the conditions imposed at every temperature except 30 degrees C, where 15 out of 42 fish died during the stress and recovery protocol. The general pattern was an initial increase in hematocrit, followed by a delayed decrease in hematocrit and chloride, and an increase in plasma glucose and cortisol. In general, fish stressed at temperatures below 20 degrees C had lower and more delayed changes in plasma glucose and cortisol than fish tested at 20, 25 and 30 degrees C. Initial cortisol concentrations were 65 ng/ml and increased to above 200 ng/ml in fish held at 20 degrees C and above. At the higher temperatures, glucose concentrations were twice the initial concentration after stress and cortisol changes were four to five times the initial concentration after the stress. Quantitative responses for glucose and cortisol were moderate and recovery rapid in fish stressed at 10 and 15 degrees C; therefore, this range of water temperature is recommended when handling sunshine bass.     

Blood respiratory properties of the mudsucker fish Labeo capensis (Smith)

For Labeo capensis (Smith) the increase in blood organic phosphates (ATP, GTP) in winter fish exceeds the increase in summer fish. Blood chlorides, blood osmotic pressure, hematocrit and hemoglobin concentration decrease significantly in winter fish when compared to summer fish. Four effectors, viz. temperature, organic phosphates, H+ and Cl-, could lower the oxygen affinity of whole blood, especially in summer fish.     

Copper and the herbicide atrazine impair the stress response of the freshwater fish Prochilodus lineatus

In order to evaluate the effects of copper and atrazine on the stress response of the freshwater fish Prochilodus lineatus, juvenile fish were pre-exposed to copper (20 μg L(-1)) or atrazine (10 μg L(-1)) for 24 h and then submitted to air exposure for 3 min. Simultaneously fish kept in dechlorinated water for 24 h were subjected to air exposure and a non-stress group was not subjected to air stress or any contaminants. Animals were sampled immediately (t0) and after 1, 3 and 6 h of air exposure (t1, t3 and t6 respectively) for the analysis of plasma cortisol, glucose and Na(+), hepatic glycogen, branchial Na(+)/K(+)-ATPase (NKA), number of red blood cells per cubic millimeter of blood (RBC), hematocrit (Hct) and hemoglobin content (Hb). In fish pre-exposed to copper the stress response was inhibited, and at t1 and t3 both cortisol and glucose remained significantly lower compared to fish subjected to air stress only. In fish pre-exposed to atrazine there was no rise in cortisol, but there was an increase in plasma glucose, RBC, Hct and Hb at t0 and a return of these parameters to basal levels at t1, as they did not differ significantly in relation to non-stressed fish. Animals pre-exposed to either Cu or atrazine showed a significant reduction in NKA activity at t1 and t3, in relation to air stressed fish. These results clearly indicate that copper and atrazine impair cortisol stress response of P. lineatus and that fish subjected to a contaminant-induced stress, either by copper or atrazine, may not be able to respond to any additional stressors.     

Effect of Hypoxia on Physiological-Biochemical Blood Parameters in Some Marine Fish

Changes of hematocrit, hemoglobin, and blood plasma glucose and Na⁺ and K⁺ content in response to hypoxia were studied in three Black Sea fish species. It was shown that in response to hypoxia in low-mobile rock perch Scorpaena porcus L., hematocrit and the blood plasma glucose level increased, while the content of K⁺ in erythrocytes decreased and the content of Na⁺ increased. In moderately mobile sea carp Diplodus annularis L. autogenic hypoxia caused a rise of hematocrit and blood plasma glucose. In actively swimming jack mackerel Trachurus mediterraneus ponticus Aleev, only considerable increase of Na⁺ content was revealed in hypoxia. The obtained results indicate that fish with different mobility under hypoxic conditions use different adaptation mechanisms. The value and direction of changes of the chosen parameters can be used to determine resistance of fish to oxygen deficit.     

Effects of acute hypoxic stress on biochemical parameters,immune regulation and metabolic capacity of the blood in genetically improved farmed tilapia (GIFT,Oreochromis niloticus)

Dissolved oxygen (DO) in the culture water is an important environmental factor in fish farming. This study tested whether genetically improved farmed tilapia (GIFT, Oreochromis niloticus) challenged with a hypoxic episode would show inhibited growth, increased metabolic stress and a reduced immune response. GIFT subjected to 72 hr of semi‐lethal hypoxia (determined by linear regression as DO = 0.64 mg/L) showed changes in blood biochemistry, energy metabolism and related immune responses. In the early stages of stress, GIFT showed increased anaerobic respiration and increased lactic acid accumulation. Compared with a control group, white and red blood cell counts, hematocrit and blood hemoglobin concentration in GIFT exposed to 4 hr of semi‐lethal hypoxic stress were not significantly changed. However, the levels of glutamic‐pyruvic transaminase, glucose, cholesterol and cortisol were significantly higher under hypoxic stress at 2 and 4 hr. In the later stages of stress, GIFT displayed increased oxygen utilization and increased aerobic respiration associated with increased red blood cell count, hematocrit and hemoglobin concentration. However, the white blood cell count, serum lysozyme and complement C3 activities began to decline, associated with increased mortality. Reverting to a normal DO environment (5.0 mg/L) for an additional 72 hr, GIFT showed strong recovery, with respiratory metabolic enzymes, immune indicators and associated energy metabolites restored to near normal levels. Our observations contribute to a better understanding of the mechanisms of energy and immune regulation in fish, and will help reduce the damage caused by hypoxic stress during culture.     

Free fatty acid metabolism in the air-breathing African catfish (Clarias gariepinus) during asphyxia

In several waterbreathing fish species, hypoxia induces a decrease in plasma free fatty acid (FFA) levels as opposed to an increase in air-breathing mammals. We hypothesised that this change is coupled to the mode of breathing. Therefore, we followed the metabolic response of cannulated air-breathing African catfish to an 8-h asphyxia period. The hematocrit and hemoglobin increased significantly upon asphyxia. However, no change was observed in the mean cellular hemoglobin concentration, indicating that more erythrocytes were brought into circulation. A continuous increase in plasma lactate concentration during asphyxia showed permanent activation of anaerobic glycolysis, pointing to a persistent oxygen shortage. Plasma glucose levels did not change, but FFA levels decreased significantly upon asphyxia with a concomitant increase in plasma noradrenaline levels. Thus, these results suggest that in the air-breathing African catfish noradrenaline mediated a decrease in plasma FFA levels similar to that in waterbreathing fish species.     

Heat shock protein (Hsp70) induced by a mild heat shock slightly moderates plasma osmolarity increases upon salinity transfer in rainbow trout (Oncorhynchus mykiss)

We have investigated whether mild heat shock, and resulting Hsp70 expression, can confer cross-protection against the stress associated with transfer from freshwater (FW) to seawater (SW) in juvenile rainbow trout (Oncorhynchus mykiss). In experimental Series I, juvenile trout reared in FW were transferred from 13.5 degrees C to 25.5 degrees C in FW, held for 2 h, returned to 13.5 degrees C for 12 h, and then transferred to 32 ppt SW at 13.5 degrees C. Branchial Hsp70 increased approximately 10-fold in the heat-shocked fish relative to the control by the end of recovery and remained high 2, 8, and 24 h post-salinity transfer. However, no clear differences could be detected in blood parameters (blood hemoglobin, hematocrit, MCHC, plasma Na(+) and plasma osmolarity) or muscle water content between heat-shocked and sham-shocked fish in SW at any sampling interval (0, 2, 8, 24, 48, 120, 240 and 360 h post-SW transfer). In experimental Series II, trout acclimated to 8 degrees C were heat-shocked at 22 degrees C for 2 h, allowed to recover 18 h, and exposed to a more severe salinity transfer (either 36 or 45 ppt) than in Series I. Branchial Hsp70 levels increased approximately 6-fold in heat-shocked fish, but had declined to baseline after 120 h in SW. Plasma osmolarity and chloride increased in both groups upon transfer to 36 ppt; however, the increase was significantly less in heat-shocked fish when compared to the increase observed in sham-shocked fish at 24 h. No significant differences could be detected in branchial Na(+)/K(+)-ATPase activity or Na(+)/K(+)-ATPase alpha1a and alpha1b mRNA expression between the two groups. Our data indicate that a mild temperature shock has only modest effects on the ability of rainbow trout to resist osmotic stress during FW to SW transfer.     

Does body size affect the response to exercise in shortnose sturgeon (Acipenser brevirostrum)?

The effect of body size on various hematological variables was examined in juvenile shortnose sturgeon (Acipenser brevirostrum) ranging in mass from 38 to 730 g. The blood was examined for differences in plasma ionic composition (Na⁺, K⁺, Cl^?), blood oxygen carrying capacities (hemoglobin, hematocrit), and plasma metabolite concentrations (lactate, glucose), before and following a standard 5‐min chasing stress. All measured resting hematological variables were size independent in shortnose sturgeon. After exercise, levels of plasma lactate, potassium, and hemoglobin increased in all fish. Only post‐exercise levels of chloride and hemoglobin changed in a size‐dependent manner; however, the relationships were weak. The general lack of a relationship between body size and hematological variables might reflect the narrow range of fish sizes used in the present study. From a practical perspective, the results suggest that when examining the hematological stress response in juvenile shortnose sturgeon, a range of fish sizes could be used. This is important considering the variability in the growth rates of juvenile shortnose sturgeon under laboratory conditions.     

Biochemical indicators of thermal stress in Tilapia aurea (Steindachner)

Tilapia aurea muscle and liver adenylate nucleotides, the adenylate energy charge (EC), plasma glucose, cortisol and chloride were monitored during acute and chronic temperature stress. Muscle EC is unaffected during acute cold water exposure but decreases significantly when tilapia are exposed to chronic, sublethal, low temperature stress. The decrease in EC is primarily the result of a decrease in ATP concentration. Plasma glucose and cortisol increase when tilapia are exposed to 11–12° C for 60 min, 11 days, and a 5-week period. Incomplete compensation is evident in 5-week acclimated fish since glucose and cortisol levels are intermediate between controls and acutely stressed fish. Acclimation to 35° C does not significantly affect plasma glucose and cortisol compared to controls (22° C). Plasma chloride is relatively unaffected by acute and chronic temperature stress. Liver adenylates are not significantly affected when tilapia are subjected to a sudden drop in water temperature (22° down to 11° C). EC is a useful indicator of chronic low temperature stress in T. aurea , while plasma glucose and cortisol are sensitive to both acute and chronic temperature stress.     

Physiological effects of dietary cadmium acclimation and waterborne cadmium challenge in rainbow trout: respiratory, ionoregulatory, and stress parameters

A suite of respiratory, acid-base, ionoregulatory, hematological, and stress parameters were examined in adult rainbow trout (Oncorhynchus mykiss) after chronic exposure to a sublethal level of dietary Cd (500 mg/kg diet) for 45 days and during a subsequent challenge to waterborne Cd (10 microg/L) for 72 h. Blood sampling via an indwelling arterial catheter revealed that dietary Cd had no major effects on blood gases, acid-base balance, and plasma ions (Ca(2+), Mg(2+), K(+), Na(+), and Cl(-)) in trout. The most notable effects were an increase in hematocrit (49%) and hemoglobin (74%), and a decrease in the plasma total ammonia (43%) and glucose (49%) of the dietary Cd-exposed fish relative to the nonexposed controls. Dietary Cd resulted in a 26-fold increase of plasma Cd level over 45 days (approximately 24 ng/mL). The fish exposed to dietary Cd showed acclimation with increased protection against the effects of waterborne Cd on arterial blood P(aCO2) and pH, plasma ions, and stress indices. After waterborne Cd challenge, nonacclimated fish, but not Cd-acclimated fish, exhibited respiratory acidosis. Plasma Ca(2+) levels declined from the prechallenge level, but the effect was more pronounced in nonacclimated fish (44%) than in Cd-acclimated fish (14%) by 72 h. Plasma K(+) was elevated only in the nonacclimated fish. Similarly, waterborne Cd caused an elevation of all four traditional stress parameters (plasma total ammonia, cortisol, glucose, and lactate) only in the nonacclimated fish. Thus, chronic exposure to dietary Cd protects rainbow trout against physiological stress caused by waterborne Cd and both dietary and waterborne Cd should be considered in determining the extent of Cd toxicity to fish.     

Methods of measuring volume changes in erythrocytes under hypoosmotic stress: a comparison

OBJECTIVE: To compare methods of analyzing changes in red blood cell volume when exposed to osmotic challenge. STUDY DESIGN: The sensitivity of different methods was tested using fish erythrocytes under hypoosmotic stress (80% and 60% saline): hematocrit ratio, Hcto(exp)/ Hcto(ctr); cellular hemoglobin mean concentration; optical density (OD400); water content; surface area estimation; mean corpuscular volume (MCV); and mean cellular hemoglobin (MCH). RESULTS: Cells exposed to both solutions demonstrated a volume increase via hematocrit ratio of 16 +/- 2% and 30 +/- 3% (p < 0.001) when exposed to 80% and 60% saline, respectively. Cellular volume estimation by OD400 revealed a change in volume only at 60% saline (26% increase). Surface area estimation suggested a difference in volume at 60% saline. MCV revealed differences in volume at < 60% saline exposure with a 33% increase and indicated a 19% increase at 80% saline. MCH showed an increase of 48% with exposure to 80% saline. CONCLUSION: The results reveal that Hcto(ctr)/Hcto(exp), MCV, OD400 and MCH yield significant volume changes and that Hcto(ctr)/Hcto(exp) is the most sensitive assay.     

Hematology and recovery response in jacundá, Crenicichla saxatilis (Linnaeus, 1758) after short‐term handling stress

The objective of this study was to evaluate the hematological response of ringtail pike cichlid ornamental fish (Crenicichla saxatilis) during the recovery period after short‐term stress. The fish were previously submitted to the stress of chasing, capture and air exposure. Assayed were 24 C. saxatilis (85.2 ± 61.6 g) in three groups of eight fish; after 0.5, 6 and 24 h recovery, blood samples were collected. The total erythrocyte, relative thrombocyte and differential leukocyte counts as well as total hemoglobin, hematocrit, glucose, total plasma protein and the red blood cells (RBC) indices of mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and MCH concentration (MCHC) were determined. Stress responses were observed after 0.5 h, although hyperglycemia remained constant during the experiment. Total lymphocyte and hemoglobin values decreased after 0.5 h in the recovery period. An increase of neutrophils and monocytosis was observed after 0.5 and 6 h, respectively. The MCHC remained stable until after 0.5 h, then varied from this time forward. MCV, MCH and erythrocyte numbers oscillated throughout the experiment. Intense stress was observed in the studied C. saxatilis, with most hematological variables not returning to their initial levels after 24 h.     

Plasma osmolarity, glucose concentration and erythrocyte responses of two Antarctic nototheniid fishes to acute and chronic thermal change

Haematocrit, haemoglobin concentration, plasma osmolarity and plasma glucose concentration of the Antarctic nototheniid fishes Pagothenia borchgrevinki and Trematomus bernacchii were monitored during 24 h periods of exposure to 3 and 6° C. The same haematological variables were also measured in P. borchgrevinki following a 5–6 week period of 4° C acclimation. The first plasma glucose measurements in acutely thermally‐stressed Antarctic nototheniids revealed a delayed hyperglycaemia which related well to the relatively slow stress‐related elevation of plasma cortisol in these species. Plasma osmolarity of both species was unchanged by acute 3° C exposure, but exhibited a delayed and transient increase during acute exposure to 6° C. Haematocrit was unaltered in T. bernacchii during the acute temperature increases but was elevated in the relatively active P. borchgrevinki . Following 5–6 weeks of warm‐acclimation (4° C) the plasma glucose concentration, haematocrit and haemoglobin concentration of P. borchgrevinki were not significantly different from fish at −1° C, but plasma osmolarity decreased toward the level found in temperate‐water teleosts.     

牛磺酸对Ⅱ型糖尿病大鼠血液流变学的影响

目的：探讨牛磺酸（taurine）对Ⅱ型糖尿病（diabetes mellitus,DM）大鼠血液流变学及氧化应激的影响。方法：将40只Wistar大鼠随机取10只为正常对照组（control组）、其余30只大鼠中取20只符合模型标准的大鼠随机分为糖尿病组（DM组）和牛磺酸治疗组（Tau组,采用20g/L牛磺酸生理盐水溶液治疗,200mg/kgbw）,前两组注射等体积的生理盐水溶液。8周后,测3组大鼠血浆葡萄糖、糖化血红蛋白、超氧化物岐化酶（SOD）、丙二醛（MDA）及血液流变学指标。结果：与对照组相比,糖尿病大鼠血糖、MDA及糖化血红蛋白明显升高,SOD活性降低,全血粘度、红细胞聚集指数、红细胞压积明显增大,红细胞变形指数减小;牛磺酸能明显降低糖尿病大鼠的血糖、MDA和糖化血红蛋白（P〈0.05或P〈0.01）,显著升高造模大鼠SOD（P〈0.01）;并且明显降低大鼠全血黏度（P〈0.05）、降低红细胞聚集指数（P〈0.05）,提高红细胞变性指数（P〈0.05）。结论：牛磺酸改善糖尿病大鼠的血液流变性可能与其提高大鼠的抗氧化能力有关,对防治糖尿病血管并发症有较好作用。     

Changes in free and total plasma cortisol levels in juvenile haddock (Melanogrammus aeglefinus) exposed to long-term handling stress

We measured changes in free and total plasma cortisol levels, plasma glucose, gill hsp70 levels, and growth in haddock (Melanogrammus aeglefinus) subjected to a long-term handling stress (15 s out of water, each day, for 4 weeks), and the effect of this long-term stress on the ability of haddock to respond to an acute stressor. The acute stressor was a single handling stress, and fish were sampled at 1, 6, and 12 h post-stress. During the long-term stress study, free and total plasma cortisol levels increased significantly (10-fold) in the stressed group after the second week. However, the percentage of free cortisol was already significantly elevated by the first week (control 17%, stressed 55%), and remained high during the second week (control 35% and stressed 65%). After 3 and 4 weeks of handling, both free and total cortisol declined in stressed fish to levels that were not significantly different from pre-stress values. Control fish grew significantly more than stressed fish (by 32% and 18%, respectively) over the 4 week study, and condition factor only increased in control fish. Although fish from the control group showed elevated total plasma cortisol levels (to 47 ng mL(-1)) 1 h after the acute stress, and the levels in stressed fish were comparable to those for the control fish, no significant increase in plasma cortisol was measured in the group subjected to the long-term stress. Free plasma cortisol levels did not increase significantly in either group following the acute stress. However, free plasma cortisol levels were significantly higher in long-term stress group, as compared with the control group, at 6 h post-stress. Plasma glucose and gill hsp70 levels were not altered by either the long-term stress or acute stressor. Our data indicate that cortisol (free and total), but not glucose or hsp70, appears to be adequate to assess short- and long-term stress in haddock.     

The effect of pH and/or calcium-enriched freshwater on gill Ca2+-ATPase activity and osmotic water inflow in rainbow trout (Salmo gairdneri)

Rainbow trout (Salmo gairdneri) were exposed to pH 5.0-5.1, 6.6 and/or calcium-enriched freshwater for 14 days. Hematocrit, gill Ca2+-ATPase enzyme activities, gill osmotic water inflow, plasma calcium and osmolarity were measured. No significant changes in plasma calcium ion levels were found. The typical increase in hematocrit usually associated with exposure of fish to acidified water was not found in the present study and is discussed. Plasma osmolarity decreased in fish exposed to calcium-enriched freshwater (60 mg Ca2+ X 1(-1) ) in comparison to fish exposed to control freshwater conditions (2 mg Ca2+ X 1(1) ), irrespective of the pH level. Gill Ca2+-ATPase enzyme activities were measured for both low affinity (3 mM Ca2+) and high affinity (100 microM) activity. Exposure of rainbow trout to low pH (pH 5.0-5.1) did not affect the specific activity of Ca2+-ATPase enzyme. However, low affinity Ca2+-ATPase activity in fish exposed to calcium-enriched freshwater did show a significant reduction. The increase in gill osmotic water permeability in fish exposed to calcium-enriched freshwater is interpreted as a result of the increase in osmolarity of the ambient media.     

The effect of water-soluble aromatic hydrocarbons on some haematological parameters of rainbow trout, Salmo gairdneri Richardson, during acute exposure

Rainbow trout were exposed to a model mixture of water-soluble aromatic hydrocarbons (AH) at concentrations of 0.3–15.2 ppm for periods of 1–72 h. None of the parameters monitored except RBC changed at 0.3 ppm AH, while all constituents, except blood glucose, changed at 7.2 ppm AH. At 15.2 ppm, all fish died within 1 h. Haematological changes included increased haematocrit, haemoglobin concentration, erythrocyte counts, and blood clotting (prothrombin) times. Plasma Cl⁻ concentration decreased significantly. Changes resembled a stress response except for the increased clotting times, which typically decrease, and lack of increase in blood glucose.     

Chronic-intermittent cold stress in rats induces selective ovarian insulin resistance

In rat ovary chronic cold stress increases sympathetic nerve activity, modifies follicular development, and initiates a polycystic condition. To see whether there is a relationship between the previously described changes in follicular development and metabolic changes similar to those in women with polycystic ovary, we have studied the effect of chronic cold stress (4 degrees C for 3 h/day, Monday to Friday, for 4 wk) on insulin sensitivity and the effect of insulin on sympathetic ovarian activity. Although cold-stressed rats ate more than the controls, they did not gain more weight. Insulin sensitivity, determined by hyperinsulinemic-euglycemic clamp, was significantly increased in the stressed animals. Insulin in vitro increased the basal release of norepinephrine from the ovaries of control rats but not from those of stressed rats, suggesting a local neural resistance to insulin in stressed rats. The levels of mRNA and protein for IRS1 and SLC2A4 (also known as GLUT4), molecules involved in insulin signaling, decreased significantly in the ovaries but not in the muscle of stressed rats. This decrease was preferentially located in theca-interstitial cells compared with granulosa cells, indicating that theca cells (the only cells directly innervated by sympathetic nerves) are responsible for the ovarian insulin resistance found in stressed rats. These findings suggest that ovarian insulin resistance produced by chronic stress could be in part responsible for the development of the polycystic condition induced by stress.     

Changes in hematological parameters in free-living pigeons (Columba livia f. urbana) during the breeding cycle

The blood parameters—red blood cell (RBC) count, hematocrit (Ht), hemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC)—were studied for the first time in free ranging pigeons Columba livia f. urbana. The aim of the study was to establish a set of reference values for this ubiquitous urban species and to examine a potential influence of the factors such as sex and phase of the breeding cycle on the hematological parameters. Blood was sampled from the adult individuals of both sexes during the breeding cycle. Significant variations in Ht and Hb were observed, while RBC count remained unchanged. The lower hematocrit value and hemoglobin concentration found in both males and females during molt probably resulted from the increase of plasma volume not accompanied by an increase in RBC. On the other hand, a significant physiological stress of nutritional deficiency during this energy-consuming stage may manifest itself in the decreased Ht and Hb values. The higher values of Ht and Hb during the laying phase could be related to the dehydration status. There were no overall differences in MCV, MCH, and MCHC values in either of the breeding stage. A lack of sex dimorphism in the measured and calculated blood parameters was apparent. Data collected herein contribute to the better understanding of general physiology of the ubiquitous urban species. The knowledge of variation in the blood indexes with respect to sex and breeding stage is crucial before blood parameters can provide an useful information on physical condition of the bird.     

Effects of Ichthyophonus hoferi on condition indices and blood chemistry of experimentally infected rainbow trout (Oncorhynchus mykiss)

Body condition, hepatosomatic index and blood chemistry of Oncorhynchus mykiss experimentally infected with a tissue dwelling fish pathogenic fungus, Ichthyophonus hoferi, were monitored over a 6 wk period. This was to determine whether the infection constituted a stress manifest by changes in the hypothalamic-pituitary interrenal axis, and especially plasma cortisol levels. Infection caused anaemia and leucopenia but did not change the condition, hepatosomatic indices, or plasma chloride, cholesterol, cortisol, creatinine, glucose, osmolarity, potassium, total protein, sodium and T4. It is suggested that increased cortisol levels may not be a normal component of the stress response of fish to disease caused by invasive infectious agents.