Histopathology, blood chemistry, and physiological status of normal and moribund striped bass (Morone saxatilis) involved in summer mortality ('die-off') in the Sacramento-San Joaquin Delta of California

Summer mortality ('die-off') is common in striped bass, Morone saxatilis (Walbaum), in the San Francisco Bay-Delta region. Tissue and blood samples of moribund and healthy striped bass collected during the summers of 1986–1988 were analysed. Sixteen moribund and 25 healthy reference fish from the Carquinez Strait area and eight fish caught in the Pacific Ocean were studied. Moribund fish plasma was invariably yellow-orange; most of the moribund fish had discoloured livers with haemorrhagic regions, and approximately one-third had haemorrhagic intestines. Piasma levels of aspartale aminotransferase, uric acid, alkaline phosphatase and cortisol were significantly higher than in reference fish from Carquinez Strait and the Pacific Ocean, whereas cholesterol, sodium, chloride, triiodothyronine and glucose levels were significantly lower. Hepatic heavy metal concentrations and bacterial content were similar in moribund and reference fish. Gill Na.⁺, K⁺ -ATPase activity was significantly lower in moribund fish. Liver, kidney, intestine, and thyroid follicles of moribund fish displayed various histopathological changes, and corticosteroidogenic (interrenal) tissue could not be identified positively in moribund fish. These findings are discussed in relation to recent work on the chemical burdens (industrial and agricultural hydrocarbons) found in livers from some of the fish examined in this study.     

Patterns of serum cortisol levels in ovariectomized females with and without androgen administration.

Serum cortisol levels in humans and primates display a circadian rhythm. A study in monkeys showed that orchiectomy abolishes this circadian rhythm. The present study compared the patterns of serum cortisol levels between 9 a. m. and 3 p. m. in two groups of ovariectomized females, one treated with testosterone (T) and one without sex steroid administration. Over the first 80 minutes of the sampling period cortisol levels declined similarly in both groups, probably due to waning of stress of the experiment. Thereafter, levels fell further in the T-administered group, but not in the group without sex steroid administration. From this pilot study it is tentatively concluded that ovariectomy, in analogy with orchiectomy in monkeys, produces a loss of a circadian pattern of cortisol levels, which is reversed by administration of T. Furthermore, upon comparison of mean serum cortisol levels in the two groups, T appeared to have a suppressive effect on values of serum cortisol levels.     

Effects of mannan oligosaccharide on the physiological responses,HSP70 gene expression and disease resistance of Allogynogenetic crucian carp (Carassius auratus gibelio) under Aeromonas hydrophila infection

We evaluated the effect of dietary supplementation with mannan oligosaccharide (MOS) on the resistance to Aeromonas hydrophi1a infection in Allogynogenetic crucian carp. The fish were randomly divided into five groups: a control group was fed with basal diet, and four treatment groups fed with basal diet supplemented with 60, 120, 240, 480 mg/kg MOS for 10 weeks, respectively. We then challenged the fish with A. hydrophi1a and recorded the mortality and the changes in serum cortisol, T3, T4, lysozyme, alkaline phosphatase (ALP), globin and hepatic total anti-oxidative capacity, superoxide dismutase (SOD), malondialdehyde (MDA) and the relative expression of heat shock protein 70 (HSP70) mRNA for a period of 7 d. Supplementation with 240 mg/kg MOS significantly increased serum ALP activity before infection, 1d and 2d after infection, serum globin concentration prior to infection, 1d and 7d after infection, serum lysozyme activity at 2d after infection, T3 concentration at 2d after infection, hepatic total anti-oxidative capacity prior to infection, hepatic SOD activity at 7d after infection and reduced serum cortisol concentration at 2d after infection, hepatic malondialdehyde content at 1d and 2d after infection. Supplementation with 480 mg/kg MOS significantly increased serum ALP activity before infection, 1d and 2d after infection, T3 content 1d after infection, T4 content prior infection and 7d after infection, serum globin concentration prior to infection, 1d and 7d after infection, serum lysozyme activity prior infection and 1d after infection, serum total anti-oxidative capacity prior to infection and 7d after infection, hepatic SOD activity at 7d after infection and the relative level of hepatic HSP70 mRNA at 2d and 7d after infection, had decreased levels of serum cortisol concentration before the infection, at 2d after infection, T4 concentration at 1d and 2d after infection, hepatic malondialdehyde content at 1d and 2d after infection. Mortality was significantly lower in the group of 240 and 480 mg/kg MOS than the control. Our results suggest that ingestion of a basal diet supplemented with 240–480 mg/kg MOS can enhance resistance against pathogenic infections in Allogynogenetic crucian carp.     

Effects of long-term cortisol treatments on gonadal development, sex steroids levels and ovarian cortisol content in cultured great sturgeon Huso huso

The objective of this study was to examine the effect of cortisol implantations on gonadal development, sex steroid levels, and ovarian cortisol content in cultured great sturgeon Huso huso. Three groups of 5 fish for each treatment were considered. The experimental groups included: control (capsules containing cocoa butter alone), low cortisol (C(5); 5mg cortisol/kg body mass+cocoa butter) and, high cortisol (C(50); 50mg cortisol/kg body mass+cocoa butter). The capsules containing hormones and cocoa butter were intraperitoneally implanted into 3-year-old female fish at pre-vitellogenic stage (mean initial body mass 6809.7 ± 73 g) every 6 weeks over a 6-month period from January to June. The serum levels of cortisol, glucose, cholesterol and sex steroids (testosterone and 17β-estradiol) were determined at the initial time and three weeks after each implantation. Oocyte histological characteristics (the diameter and area of the oocyte, the diameter and area of the nucleus and the ratio of the nucleus area to the oocyte area) were measured at the end of the experiment and compared to those at the initial time. Ovarian cortisol content was measured at the end of the experiment. The results showed that serum cortisol levels varied in a dose-independent manner, so that the highest cortisol concentrations were observed in C(5)-treated fish throughout the experiment. Serum glucose levels were significantly higher in cortisol-treated groups than those in the control group. The high dose of cortisol elicited a significant constant increase in serum cholesterol concentrations. Fish implanted with the high cortisol dose showed significant declines in serum testosterone and 17β-estradiol concentrations throughout the experiment. No significant differences were found in oocyte histological characteristics among experimental groups. The cortisol implants elicited a dose-dependent increase in ovarian cortisol content. At the end of trial, body-growth indices were the lowest in C(50)-implanted fish, while the low cortisol dose had no effect on growth relative to the controls. These results indicated that chronic stress induced by cortisol implantation in great sturgeon suppressed gonadal steroidogenesis and somatic growth but had no effect on ovarian growth and development.     

Relationship between eyed-egg percentage and levels of cortisol and thyroid hormone in masu salmon Oncorhynchus masou

A possible cause of the low eyed-egg percentage that afflicts pond-reared masu salmon Oncorhynchus masou at a fish hatchery (Kumaishi Fish Hatchery, Hokkaido, Japan) was investigated. Serum cortisol levels of masu salmon during the spawning period were compared between individuals from Kumaishi and those from another station (Mori). Cortisol, thyroxine (T₄) and triiodothyronine (T₃) hormones were also measured in eyed eggs and their levels were compared to the eyed-egg percentage. Serum cortisol levels were significantly higher at Kumaishi than at Mori in May and July of the breeding season. At the Kumaishi station, there was a linear positive relationship between serum cortisol and fertilized-egg cortisol levels of female masu salmon. As cortisol levels in both ovulating females and eyed eggs increased, the eyed-egg percentage decreased, indicating a highly significant negative relationship between cortisol levels and eyed-egg percentage. In contrast, as T₃ and T₄ levels in eyed eggs increased, the eyed-egg percentage increased. The strong positive correlation between high cortisol levels in serum and in eyed eggs at Kumaishi indicates that the frequently higher cortisol levels may have caused the lowering of the eyed-egg percentage.     

Effect of high‐dose vitamin C supplementation on growth,tissue ascorbic acid concentrations and physiological response to transportation stress in juvenile silver pomfret,Pampus argenteus

This study investigated the effect of high‐dose vitamin C supplementation on growth, tissue ascorbic acid concentrations and physiological response to transportation stress in juvenile silver pomfret, Pampus argenteus (initial average weight 6.2 ± 0.2 g). Three practical diets were formulated to contain 100 (control), 450 and 800 mg ascorbic acid/kg diet, respectively, supplied as l‐ascorbyl‐2‐polyphosphate. Each diet was fed to triplicate groups of fish in circular tanks (3 m ø, 1.5 m depth) (60 fish/tank) for 9 weeks. Growth did not change significantly with dietary vitamin C levels, although an improvement tendency with an increase in vitamin C supplementation was observed. Ascorbic acid concentrations in the liver and muscle of fish fed diets containing graded levels of vitamin C were positively correlated with dietary levels of this vitamin. Tissue ascorbic acid concentrations significantly increased with increasing vitamin C supplementation. After 9 weeks, the fish were subjected to transportation stress for 4 h to determine the influence of high vitamin C supplementation on the physiological response to this stressor. Serum cortisol, glucose and lactate levels significantly increased in stressed fish. Serum cortisol and glucose concentrations after stress were significantly higher in fish fed the control diet (7.91 μg L^?1 and 0.80 mm , respectively) than in the other groups. However, there were no significant differences in serum cortisol and glucose levels after stress between the 450 and 800 mg kg^?1 diets. No significant change could be found in serum lactate levels after stress among the different treatments. In conclusion, the dietary administration of high doses of vitamin C could reduce stress in silver pomfret and increase the survival of fish under stress conditions.     

大黄葸醌提取物对建鲤抗应激及生长的影响

将750尾建鲤随机分成5组,第1组为对照组,投喂基础日粮,另外4组为试验组,投喂基础日粮中分别添加0．5％、1．0％、2．0％、4．0％大黄蒽醌提取物。从2005年7月到9月连续投喂70d后,对鱼体进行高密度应激,测定其生长、应激前后血液皮质醇、血糖、溶菌酶等变化。结果表明：与对照组相比,应激前添加大黄葸醌提取物提高了鱼体增重率、特定生长率、鱼体丰满度、血液溶菌酶活性,降低了饵料系数与鱼体死亡率,但是与大黄葸醌提取物的添加水平不成线性关系,其中2．0％试验组还显著降低了血液皮质醇。高密度应激1d后,各组血液中的皮质醇、血糖、溶菌酶都有不同程度的增加,其中对照组最高,添加1．0％和2．0％大黄蒽醌提取物的试验组相对较低。应激前后各组鱼的攻毒试验表明：除应激前添加1．0％和2．0％大黄蒽醌提取物的组没有死鱼外,其它各组都有死鱼,其中对照组死亡率最高。因此添加1．0％-2．0％大黄蒽醌提取物提高了机体抗应激能力,并对病原菌感染起一定的保护作用,促进了鱼体生长。     

大黄蒽醌提取物对建鲤抗应激及生长的影响

将750尾建鲤随机分成5组,第1组为对照组,投喂基础日粮,另外4组为试验组,投喂基础日粮中分别添加0.5%、1.0%、2.0%、4.0%大黄蒽醌提取物。从2005年7月到9月连续投喂70d后,对鱼体进行高密度应激,测定其生长、应激前后血液皮质醇、血糖、溶菌酶等变化。结果表明:与对照组相比,应激前添加大黄蒽醌提取物提高了鱼体增重率、特定生长率、鱼体丰满度、血液溶菌酶活性,降低了饵料系数与鱼体死亡率,但是与大黄蒽醌提取物的添加水平不成线性关系,其中2.0%试验组还显著降低了血液皮质醇。高密度应激1d后,各组血液中的皮质醇、血糖、溶菌酶都有不同程度的增加,其中对照组最高,添加1.0%和2.0%大黄蒽醌提取物的试验组相对较低。应激前后各组鱼的攻毒试验表明:除应激前添加1.0%和2.0%大黄蒽醌提取物的组没有死鱼外,其它各组都有死鱼,其中对照组死亡率最高。因此添加1.0%-2.0%大黄蒽醌提取物提高了机体抗应激能力,并对病原菌感染起一定的保护作用,促进了鱼体生长。     

Heat stress-induced modulation of host defense against Toxoplasma gondii infection in mice

This study examined the effects of burn injury on murine immune response against Toxoplasma gondii infection. Male C57BL/6 mice were divided into 3 groups: T. gondii infection (group T), burn injury (group B), and burn injury followed by T. gondii infection (group BT). The survival of group BT was significantly lower than those of group B and group T. Parasite abundance in the tissues was determined by quantitative competitive-polymerase chain reaction. Group BT exhibited significantly higher numbers of T. gondii than group T. Antibody production against T.g.HSP30 in group BT was significantly lower than that in group T, whereas no significant difference was observed in SAG1-specific antibody production. Delayed-type hypersensitivity (DTH) specific for 2,4-dinitrofluorobenzene (DNFB) of both group B and group BT was significantly lower than that of group T. One week after infection, serum interferon-gamma (IFN-gamma) and interleukin (IL)-10 levels in group BT were significantly lower, whereas serum IL-6 levels were significantly higher than in group T Serum TNF-alpha levels in both group T and group BT were elevated at 1 wk after infection, although there was no significant difference between them. Serum IFN-gamma, IL-10, and TNF-alpha levels in group B were not elevated during the experimental term. In conclusion, the impaired antigen-specific antibody production and DTH response, together with the modulated patterns of cytokine responses, seemed to be strongly involved in the development of burn-induced immunosuppression and the consequent increased susceptibility to T. gondii infection in mice.     

Experimental exposure of rainbow trout Oncorhynchus mykiss (Walbaum) to the infective stages of the sea louse Lepeophtheirus salmonis (Krøyer) influences the physiological response to an acute stressor

The influence of infection with the juvenile stages of the sea louse, Lepeophtheirus salmonis (Kr?yer) on the response of rainbow trout Oncorhynchus mykiss (Walbaum) to a net confinement protocol was investigated. The experiment consisted of two groups of seawater-adapted rainbow trout, one which was exposed to a total of 4000 nauplii/copepodid stages of L. salmonis 30, 25 and 14 days prior to confinement. Confinement elicited a greater stress response in the lice-exposed fish, than in the controls, as seen by higher plasma cortisol and glucose levels. A reduced spleen somatic index in exposed fish following 6 h confinement coincided with increased erythrocyte and lymphocyte numbers in the blood. Circulating lymphocyte numbers were significantly reduced in both groups 24 h post-confinement, when a lower alternative complement activity was recorded in control fish. Prior to confinement, lice-exposed fish had an elevated serum lysozyme activity and reduced oxygen radical production by blood leukocytes. Following confinement, lysozyme activity was gradually reduced in lice-exposed trout. During confinement, oxygen radical production decreased in control fish and increased in infested fish. Overall, transient exposure to juvenile lice altered the response to a second stressor, which has implications for management procedures of L. salmonis exposed fish.     

Changes in serum thyroxine levels during smolting in captive and wild Atlantic salmon, Salmo salar L.

On a commercial fish farm in Western Scotland, smolting Atlantic salmon, Salmo salar L., showed no major changes in serum thyroxine (T4) levels in the spring. In contrast, serum T4 levels in smolting, wild salmon, trapped as they left the Girnock Burn, Aberdeenshire, varied markedly over this period. Serum T4 levels were correlated with the stream discharge rate pertaining as the fish left the stream. Levels in migrating, smolting fish were higher than those in fish captured above the fish-trap by electro-fishing. In a stream channel, serum T4 levels in smolting fish caught previously in the fish-trap were rapidly elevated by exposure to increased water-flow, whereas levels in fish previously captured above the trap remained substantially unchanged. Serum T4 levels in salmon parr leaving the stream in autumn were generally lower than those in smolting fish leaving in spring and were not demonstrably affected by stream discharge rate.     

The response to capture and confinement stress of plasma cortisol, plasma sex steroids and vitellogenic oocytes in the marine teleost, red gurnard

Reproductively active female red gurnard Chelidonichthys kumu were captured on long-lines, and placed in confinement tanks for 24, 48, 72 and 96 h to examine the effect of capture and confinement on reproductive parameters (experiment I). Plasma cortisol at the time of capture was elevated to levels typical of stressed fish in other species (53–125 ng ml⁻¹). Final plasma cortisol levels in red gurnard confined for any length of time were not significantly different from one another (ranging from 17 to 43 ng ml⁻¹), indicating that fish were chronically stressed when held in captivity for up to 96 h after capture. When initial and final plasma cortisol levels were compared within confinement groups, cortisol decreased significantly after 24 and 96 h of confinement indicating that some acclimation to captivity may have occurred. In contrast, plasma 17β-estradiol (E₂) and testosterone (T) levels decreased significantly to levels comparable to those in post-spawned fish, after any period of confinement, and remained low throughout the experiment. Another group of fish was captured and confined in the same manner as experiment I but subjected to repeated blood sampling every 24 h, until 96 h post-capture. In these fish, plasma cortisol levels decreased significantly from 127 ng ml⁻¹ after 24 h confinement and thereafter showed no change (25–45 ng ml⁻¹). Plasma E₂ decreased significantly after 72 h of confinement while plasma T showed no change from levels at capture. Increased amounts of follicular atresia were found in vitellogenic oocytes of fish confined for longer periods of time in experiment I, indicating that capture and confinement stress affect reproduction negatively in captive wild fish.     

Thyroid function, pituitary structure and serum lipids in Great Lakes coho salmon, Oncorhynchus kisutch Walbaum, 'jacks' compared with sexually immature spring salmon

Whereas spring salmon, Oncorhynchus kisutch , from Lake Ontario had no overt thyroid goiters, comparable Lake Erie spring salmon had a 44% goitre incidence. Goitre incidence in sexually precocious 'jacks' from Lakes Ontario and Michigan was 43–45% and 100% in 'jacks' from Lake Erie.
All fish displayed thyroid hyperplasia. The degree of hyperplasia (as indicated by thyroid follicle colloid content, thyroid follicle size and shape and thyroid follicle epithelial cell size) in Lake Ontario fish tended to be greater in the 'jacks' than in the spring fish; the reverse was true in Lake Erie fish. Serum total L-thyroxine (T4) concentrations in Lake Ontario spring fish were higher than in any other group. There were no differences in serum T, levels between the groups of 'jacks', nor were serum T, levels in 'jacks' and spring salmon from Lake Ontario significantly different. Serum total triiodo-thyronine (T) concentrations in Lake Ontario spring salmon were significantly higher than in all other groups and that in Lake Erie spring salmon greater than in all groups of 'jacks'. Serum T, levels in Lake Ontario 'jacks' were higher than in Lake Erie 'jacks'. Serum free fatty acid (FFA) and cholesterol levels showed significant interlake differences with lower levels present in Lake Erie salmon. Lake Erie 'jacks' appeared to have fewer and less well vacuolated pituitary gonadotropic basophils than 'jacks' from Lakes Michigan and Ontario. Putative thyrotrop cells appeared to be more numerous and more active in the Lake Erie spring salmon compared with Lake Ontario spring salmon. Prolactin, corticotrop and melanotrop cells appeared less active in spring salmon than in the 'jacks'.     

The effects of vitamin E on antiacid stress ability in juvenile soft-shelled turtles (Pelodiscus sinensis)

We determined the effect of dietary supplementation with vitamin E (0-, 50-, 250-, 500-, 1000- and 5000-mg/kg diet for 4 weeks) on antistress ability in juvenile soft-shelled turtle (Pelodiscus sinensis). Half of the turtles per dose group were treated by acid stress for 24 h. The results showed that phagocytosis of blood cells in the control group significantly decreased after acid stress while the other five groups had no significant changes compared with those of before stress. Serum bacteriolytic activity in the control group and the group supplemented with 50-mg vitamin E/kg diet significantly decreased after acid stress. The other four groups showed no significant differences compared with those before stress. Serum bactericidal activities in all groups notably decreased after acid stress, but the difference of serum bactericidal activity in before and after stress had a decreased tendency from the control group to the highest dose group. Serum cortisol levels in the control group were significantly increased while the other five groups had no notable increases after acid stress. Liver vitamin E levels in all groups had no notable changes compared with those before stress but there was a tendency to decrease after acid stress. These results suggest that acid stress depress immune function and increase serum cortisol levels in turtles while vitamin E alleviate the adverse effects caused by acid stress.     

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.     

Effects of social isolation on growth,stress response,and immunity of zebrafish

Stressful housing conditions like social isolation have been shown to profoundly affect the physiology and health of various organisms which is rarely addressed in fish species. In the present study, we used a shoaling species, zebrafish, to investigate the stress reactivity of grouped and individually housed fish. We also hypothesized if isolation is a stressful condition may disrupt growth performance and innate immune response of individuals. To this end, fish were housed individually (social isolated treatment) or in groups of five fish (control treatment) for 60 days. Growth indices of fish were not affected by social isolation. Sixty-day social isolation did insignificant effect on baseline cortisol levels of specimens; however, individually housed zebrafish showed lower plasma cortisol to chasing stress than the control grouped fish. On the contrary, exposure to predator caused higher cortisol levels in social isolated fish. Serum lysozyme activity of isolated individuals was significantly lower than control fish, but activity of serum complement remained unchanged. Our results represent evidences that zebrafish experienced social isolation showed broad changes in physiological and immunological functions which may affect the quality of life.     

Metabolic changes induced by combined prolonged exercise and low-calorie intake in man

Thirteen middle-aged women and 10 men walked 344 km during 7 days. The daily walking distances were 57, 53, 67, 53, 41, 36, and 37 km at an average speed of 3.5 km X h-1. During the hike the subjects drank water, mineral drinks, and juices ad libitum. Except for some natural products, no food intake was allowed. During the hike the body weight and serum protein concentration of the subjects decreased by about 7%, on average. Serum triglyceride and total cholesterol decreased drastically, about 30-40% during the hike, but HDL-cholesterol showed a tendency to increase, giving a 40% increment in HDL/total cholesterol ratio. Serum free fatty acids rose 1.5-2 times above the starting level. Serum glucose and evening insulin levels decreased significantly during the hike. Serum cortisol in evening samples after the daily walking and plasma norepinephrine concentrations were significantly increased, reflecting the immediate daily response to the combined fasting and walking. Serum testosterone levels decreased in men but not in women, indicating the involvement of the LH-testis pathway in the decrease obtained. Serum ASAT activity rose to about three times the starting level during the hike, whereas gamma-GT activity gradually decreased. These marked metabolic changes caused by combined fasting and several days exercise were in many respects (as in cholesterol, HDL/total cholesterol ratio or testosterone levels) more pronounced than those earlier reported to be caused by exercise or fasting alone.     

The effect of sublethal endrin exposure on rainbow trout, Salmo gairdneri Richardson. I. Evaluation of serum cortisol concentrations and immune responsiveness

Two-hundred-and-forty rainbow trout, Salmo gairdneri , were exposed for 30 days to sublethal concentrations of the pesticide endrin. On day 30, ten fish from each treatment group were sacrificed and examined for the ability of peritoneal macrophages to phagocytize latex beads. The remaining fish were immunized with 10 μg of Yersinia ruckeri O-antigen, and exposure to endrin continued. The migration inhibition factor assay (MIF), plaque forming cell assay (PFC), and serum agglutination titres (SAG) were performed 2, 14, and 30 days post-antigen inoculation. Serum was collected from all fish for serum cortisol concentrations. Endrin exposure had no effect on the phagocytic ability of peritoneal macrophages. However, the MIF, PFC and SAG responses were significantly reduced from control values. Serum cortisol concentrations were found to be significantly elevated in endrin-exposed fish. Serum cortisol concentrations were found to be significantly higher on days 44 and 60 (192 and 194 ng ml⁻¹, respectively) when compared to days 30 and 32 (159 and 141 ng ml⁻¹, respectively). Cortisol values for days 30 and 32 did not differ significantly, nor did those of days 44 and 60. The relationship between elevated serum cortisol concentrations and endrin exposure on the immune response is discussed.