Ontogeny of the cortisol stress response in yellow perch (Perca flavescens)

The ontogeny of the cortisol stress response in yellow perch (Perca flavescens) was documented by measuring resting and stress-induced whole-body cortisol levels in fish at several early development stages. In newly fertilized eggs resting cortisol levels averaged 41.0 ± 3.0 pg/embryo, and decreased to 8.0 ± 3.0 pg/embryo by day 6 where they remained constant until hatch on day 10. Acute stress challenge tests (30 sec cold shock) conducted on embryonic (days 6 and 8 post-fertilization) and larval (hatch and 2 days post-hatch) yellow perch revealed no differences in whole-body cortisol levels between stressed and unstressed individuals. In acute stress challenge tests (30 sec net confinement) conducted on post-hatch yellow perch, differences in cortisol levels between stressed (30 min post-stress) and unstressed fish were detected one week after hatching (12.3 ± 1.6 ng/g and 7.0 ± 1.3 ng/g, respectively). The magnitude of the stress response was greater in 2- to 5-week-old fish than in one-week-old fish. Changes in post-stress cortisol levels were closely associated with changes in interrenal morphology. Cumulatively, these results indicate that cortisol biosynthesis, integration and maturation of the hypothalamic-pituitary-interrenal (HPI) axis can be observed in yellow perch as early as one week after hatching. This revised version was published online in July 2006 with corrections to the Cover Date.     

The settlement and reproductive success of Lepeophtheirus salmonis (Krøyer 1837; Copepoda: Caligidae) on atypical hosts

The reproductive success of Lepeophtheirus salmonis settled on host and non‐host fish has been compared. Triplicate single species tanks of Atlantic salmon, marine three‐spined sticklebacks, saithe and Atlantic cod were exposed to 10 adult female L. salmonis per tank (n=30 lice per species). Adult female L. salmonis settlement and egg string production occurred only on salmon and cod, with no egg production occurring on saithe and three‐spined sticklebacks. The number of eggs in egg strings, hatching success of eggs and the survival of all larval stages to the copepodid stage were severely affected by the species of fish on which female L. salmonis had settled. L. salmonis settled on cod produced significantly fewer eggs, lower hatching rates and lower survival rates of larvae than females on Atlantic salmon. The production of egg strings by L. salmonis females infecting cod, which successfully hatch and moult through to the infective copepodid stage, albeit in small numbers, is discussed in terms of the implications to aquaculture and salmon and cod farming scenarios.     

Oxidative stress in juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum), were held in 8–11°C freshwater, starved for 3 days and subjected to a low‐water stressor to determine the relationship between the general stress response and oxidative stress. Lipid peroxidation (LPO) levels (lipid hydroperoxides) were measured in kidney, liver and brain samples taken at the beginning of the experiment (0‐h unstressed controls) and at 6, 24 and 48 h after application of a continuous low‐water stressor. Tissue samples were also taken at 48 h from fish that had not been exposed to the stressor (48‐h unstressed controls). Exposure to the low‐water stressor affected LPO in kidney and brain tissues. In kidney, LPO decreased 6 h after imposition of the stressor; similar but less pronounced decreases also occurred in the liver and brain. At 48 h, LPO increased (in comparison with 6‐h stressed tissues) in the kidney and brain. In comparison with 48‐h unstressed controls, LPO levels were higher in the kidney and brain of stressed fish. Although preliminary, results suggest that stress can cause oxidative tissue damage in juvenile chinook salmon. Measures of oxidative stress have shown similar responses to stress in mammals; however, further research is needed to determine the extent of the stress–oxidative stress relationship and the underlying physiological mechanisms in fish.     

Sex-related differences in the organismal and cellular stress response in juvenile salmon exposed to treated bleached kraft mill effluent

Exposure of fish to stressors can elicit biochemical and organismal changes at multiple levels of biological organization collectively known as stress responses. The organismal (plasma glucose and cortisol levels) and cellular (hepatic hsp70) stress responses in fish have been studied in several species, but little is known about sex-related differences in these responses. In this study, we exposed sexually immature juvenile chinook salmon (Oncorhynchus tshawytscha) to bleached kraft mill effluent (BKME: 0%, 1%, and 10% v/v) for 30 days and then measured components of their organismal and cellular stress responses. Males exposed to 1% BKME had higher levels of plasma glucose than females. Plasma cortisol levels were unaffected in females exposed to BKME, but males exposed to 10% BKME had significantly higher levels of plasma cortisol relative to non-exposed males. While exposure to BKME did not affect hsp70 levels in males, females exposed to 1% BKME had higher levels of hsp70 relative to non-exposed and 10% BKME groups. Within any given treatment, females had higher levels of hsp70 relative to males. This study demonstrates that sex-related differences exist in commonly used indicators of stress in fish, and points out the importance of considering the sex of the fish in stress research. This revised version was published online in July 2006 with corrections to the Cover Date.     

Puerarin Promotes Overall Health Through Blood Flow and Immune Response within Chinook Salmon (Oncorhynchus tshawytscha) Fingerlings

An 8-week study was performed to determine the effects of supplementing puerarin, the most biologically active ingredient present in the roots of kudzu (Puerarin lobata), in diets of farmed chinook salmon (Oncorhynchus tshawytscha) fingerlings. Puerarin was given to study fish through supplementation to commercial fish feed. Administration of puerarin reduced cortisol, proteins, and hematocrit levels while improving spleen somatic indices and respiratory burst response compared to fish fed a control diet without affecting growth, and thereby counteracts the negative consequences of stress induced through handling and experienced by fish reared in aquaculture.     

Growth Acceleration of Seawater-Adapted Female Chinook Salmon Oncorhynchus tshawytscha by Constant Infusion of Recombinant Bovine Growth-Hormone Under Ambient Summer Conditions

Seawater-adapted female chinook salmon ( Oncorhynchus tshawytscha ) in their second summer were treated with one of three doses of recombinant bovine growth-hormone (rbGH) administered in a continuous fashion by osmotic pump for approximately five weeks. Untreated fish, sham-treated fish and fish treated with the low dose of hormone (0.003 μg/g bwt/day) did not differ significantly in their growth performance over the 10 week course of the experiment. By the end of the treatment period (week 6) the mean increases in fork length and weight for these groups were 7.6% and 38.9%, respectively. A dose-dependent enhancement of growth was observed for the fish treated with the mid (0.016 μg/g bwt/day) and high (0.078 μg/g bwt/day) doses of hormone. After 6 weeks, the fish given the mid dose of rbGH had gained 9.6% in fork length and 45.3% in weight, while the fish treated with the high dose of rbGH had gained 13.9% in fork length and 52.9% in weight. A significant increase in specific growth rate was observed for these latter two groups during the treatment period while condition factor declined in response to the high dose of rbGH. This experiment indicates that chronic administration of growth-hormone to chinook salmon can result in a dose dependent elevation of growth rate. Results are discussed in relation to previous attempts to accelerate the growth of Pacific salmon with growth-hormone and the potential for using recombinant growth-hormone to improve the production characteristics of salmon being cultured in seawater.     

Changes in thyroid hormone levels in eggs and larvae and in iodide uptake by eggs of coho and chinook salmon,Oncorhynchus kisutsch andO. tschawytscha

Developmental profiles of thyroxin (T₄), triiodothyronine (T₃) and radioactive iodide uptake were established for eggs and T₄ and T₃ profiles were established for larvae (whole-body, yolk-only and body-only) of coho and chinook salmon. T₄ and T₃ were consistently present in all samples. In eggs, hormone levels remained fairly constant in all cohorst for at least the first three weeks of incubation, but then fluctuated in both directions in some sample groups. Large increases in T₄ (from 9 ng/g to 245 ng/g) were seen in 1985 chinook eggs 28 days after fertilization. Radioactive iodide uptake (which was used as a possible indicator of thyroxinogenesis) increased at least 10-fold in both 1986 coho and chinook eggs from 23–30 days after fertilization. T₄ (62 ng/g) and T₃ (393 ng/g) were found in the bodies of 28-day-old 1986 chinook embryos. In whole larvae, hormone levels varied depending upon the cohort studied. In general, initial body-only concentrations of both T₄ and T₃ decreased as body weight increased, but before yolksac resorption was completed, both thyroid hormone content and concentration increased (except for chinook T₃). T₄ and T₃ content in larval yolk stayed constant as yolksac size decreased, resulting in increased thyroid hormone concentration in the yolksac. All of these data suggest that the initial source of thyroid hormones in coho and chinook salmon eggs is maternal, but that by approximately 3–4 weeks after fertilization, the developing embryos begin to produce their own thyroid hormones. After hatching, increases in tissue T₄ and T₃ concentration coupled with constant T₄ and T₃ content in diminishing yolksacs suggest that larvae also produce their own thyroid hormones; yolksac content then may reflect both the original maternal hormones and the larva-producted hormones.     

Cortisol response of golden shiners (Notemigonus crysoleucas) fed diets differing in lipid content

The purpose of this study was to characterize the plasma cortisol response in golden shiners (Notemigonus crysoleucas) under crowding stress, and to determine whether dietary lipid affects the cortisol response. The main differences between the diets were the relative amounts and types of fatty acids of the n-3 and n-6 families. In experiment 1, triplicate groups of golden shiners were fed diets with 4 or 13% menhaden fish oil, or 4 or 13% poultry fat at 3% body weight for 4 weeks before the crowding stress. In experiment 2, fish were fed diets with 8% lipid from soybean oil (SBO), cod liver oil (CLO), (SBO+CLO), or cottonseed oil (CSO) for 6 weeks before the stress test. Plasma cortisol was measured initially, two hours after the stressor was applied, and two hours after the stressor was removed. The overall pattern of the cortisol response was similar to that seen in other warmwater fishes, but the rate and magnitude of the response were not affected by diet in either experiment. Golden shiners have an intermediate cortisol response compared to other fish that have been exposed to similarly stressful conditions.     

Effects of rearing stress on Atlantic salmon (Salmo salar L.) antibody response to a non-pathogenic antigen

This study was carried out to test the effects of acute stress on the primary and the secondary antibody responses in Atlantic salmon (Salmo salar L.). Fish received a primary immunization with sheep red blood cells (SRBC) and received a second immunization 11 weeks later. At priming, a group of fish was stressed by water level reduction for 30 min (moderate stress), and another group was stressed severely by applying the stressor twice, with an interval of 6 h, 3 days in a row (severe stress). At the time of the booster, another two groups of previously unstressed, primed fish were treated likewise. Unstressed fish mounted a primary antibody response to SRBC and a secondary response, which was improved compared with the primary response., The primary antibody response against SRBC was impaired by severe, but not moderate, acute stress at priming, whereas the secondary antibody response was unaffected. Both moderate and severe stress at the time of the booster was immunosuppressive in fish that had been primed under non‐stress conditions. It is concluded that cortisol release as a result of stress exposure is most immunosuppressive at the time of the second immunization.     

Reproductive biology,early ontogeny,and effect of temperature on development in wolffish: comparison with salmon

Peculiarities of reproduction, early ontogeny, methods of egg incubation, and influence of temperature on development are compared in wolffish (Anarhichas lupus L.) and in salmonids, mainly Atlantic salmon (Salmo salar L.). Reproductive indices of females are similar in both species, but differ in males due to the small production of sperm in wolffish, a difference explained by internal fertilization in the latter species. The rate of embryonal development until the beginning of differentiation of fin fold at the same temperature is similar in both species, but the period from activation to hatching is more than twice as long in wolffish as in Atlantic salmon. Wolffish hatch at a more advanced stage with a small remnant of yolk sac and begin to feed shortly thereafter. As in Atlantic salmon, eggs and larvae of wolffish have a wide range of temperature resistance except before and after hatching. Based on the difference of life cycles in wolffish and salmon, technologies for their artificial breeding are compared.     

The effect of allostatic load on hypothalamic–pituitary–interrenal (HPI) axis before and after secondary vaccination in Atlantic salmon postsmolts (Salmo salar L.)

The experiment consisted of three experimental groups: (1) “vaccine and stress”, (2) “stress and vaccine” and (3) control. All groups have previously been vaccinated 6 months prior to the start of the experiment. At the start of the experiment, the “vaccine and stress” group was vaccinated with Pentium Forte Plus for the second time (25.02.2008) and then given a daily stressor (confinement stressor 267 kg m-3 in 15 min) for a period of 4 weeks. The “stress and vaccine” group was given a similar daily stressor for 4 weeks and then vaccinated for the second time. The control group was neither stressed nor vaccinated a second time. The results indicates that fish in the “stress and vaccine” group may have entered an allostatic overload type 2 due to oversensitivity to ACTH, a reduced efficient negative feedback system with elevated baseline levels of plasma cortisol and reduced immune response with pronounced effects on the well-being of the animal. The “vaccine and stress” group may likewise have entered an allostatic overload type 1 response, with oversensitivity to ACTH and transient reduced efficient negative feedback system. This study shows that if plasma cortisol becomes elevated prior to vaccination, it could perhaps instigate an allostatic overload type 2 with dire consequences on animal welfare. To reduce the risk of compromising the animal welfare during commercial vaccination of salmon, one propose to grade the fish minimum a week prior to vaccination or grade simultaneously with vaccination. This could reduce the overall allostatic load during handling and vaccination and secure a healthy fish with intact immune response and improved animal welfare.     

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.     

A study of bacteria present within unfertilized salmon eggs at the time of spawning and their possible relation to early lifestage disease

Abstract. The eggs of 30 female chinook salmon, Oncorhynchus tshawvtscha (Walbaum), were collected at spawning. Some eggs from each fish were collected for bacteriologic study. Two salmon produced eggs judged to be of poor quality which were not used. The remaining 28 of the 30 groups of eggs were fertilized from a single sperm pool and the eggs incubated in separate groups. Mortality data on the developing salmon were recorded regularly through the twelfth week on feed. Unfertilized eggs from each group were surface-disinfected with an iodine solution, then crushed and subjected to a culture procedure designed to permit growth of as many bacterial types as possible. Bacteria were cultured and identified, and a comparison made of the types of organisms present in eggs from groups which later incurred high or low mortalities. Bacteria were recovered from both groups of salmon eggs. Although no single organism could be identified as a cause of increased mortality, the more frequent occurrence in the eggs of the 'high mortality' group of species of Vibrio, Listeria, Corynebacterium and Staphylococcus suggests that these bacteria may play a role. It is suggested that the cause of so-called early lifestage disease of salmon is multifactorial.     

Egg cortisol response to stress at early stages of development in Persian sturgeon Acipenser persicus

One of the most important periods in artificial breeding of sturgeon is incubation. In general, little is known about ontogeny of the stress response in early developmental stages of sturgeon. In this study, cortisol content was measured by radioimmunoassay for the first time in eggs of Persian sturgeon Acipenser persicus to elicit at which times during early developmental stages, that they were particularly sensitive to stressful events. In this study, fertilized eggs of mature Persian sturgeons were placed in special boxes (as replicates) that were put in incubation units of Yushchenko. To assess pre-stress samples (resting cortisol levels), 5 eggs were selected randomly from each box in 7 important stages of incubation (2-cell division, blastula, end of blastula, mid of gastrula, neurula, eyed stage and heart beaten). In another experiment, eggs were exposed to an acute stress (10 min out of water) in 7 developmental stages. For determination of post-stress cortisol, eggs were collected 2 and 6 h after the stress. The results indicated significant difference in various stages of incubation but cortisol levels revealed no differences in whole-body levels between stressed samples (2 and 6 h post-stress) and unstressed samples (P > 0.05). The highest percentage of hatching rate for post-stressed eggs was recorded in 2-cell division stage while this percentage declined steadily in the heart beaten stage when a statistically significant difference was revealed with regard to other stages (P = 0.000). These findings suggested that sturgeon eggs were not so much sensitive in their early developmental stages and relatively resistant to stress. However, significant decrease in survival rate in heart beaten stage showed a sensitivity of this stage to stress. Lack of an increase in cortisol after acute stress indicated that hypothalamus-pituitary-interrenal (HPI) axis for cortisol synthesis was not yet functional. However, further studies seem necessary to clarify when HPI axis is activated in this species.     

Induced ovulation of female chinook salmon (Oncorhynchus tshawytscha) at a production hatchery

A simple, low-cost method for inducing ovulation in hatchery-held adult chinook salmon was developed. Use of this method resulted in an increase in the number of eggs collected, by circumventing losses due to prespawning mortality.One hundred and twenty 4-year-old chinook salmon which had returned to the Capilano hatchery prior to 1 October were used as a stock population. Three weeks before the peak spawning period, 36 fish were divided into two groups. The control group received two injections of 0.65% saline spaced 3 days apart. The test group received a 0.1-mg/kg SG-G100 (salmon gonadotropin) injection, followed on the third day by a 2.5-mg/kg SG-G100 injection. By Day 8, 73% of the treated group and 0% of the control group had ovulated. Prespawning mortality accounted for 22% of the treated fish and 83.4% of the control fish. Treatment resulted in a net gain of 16,000 eggs over the control. The second experiment began 3 days before the peak spawning period. The 32 fish which remained in the stock population were divided into three groups and received two injections 3 days apart. The two treatment groups received either 0.1 mg SG-G100/kg followed by 2.0 mg SG-100/kg, or 0.1 mg SG-G100/kg followed by 50.0 mg salmon pituitary extract (SPE)/kg. The control group was injected with 0.65% saline. By Day 8, 73% of the SPE group, 82% of the SG-G100 group, and 40% of the control group had ovulated. Treatment resulted in a net gain of 16,000 eggs for the SG-G100 group and 19,000 eggs for the SPE group over the control. No significant differences in egg size or percent survival to the eyed stage were found between test and control groups. The misjudgment of maturity led to the stripping of several fish before their eggs were completely ovulated. The factors leading to these partial ovulations are discussed.     

Suspending Mammalian LHRHa‐injected Channel Catfish,Ictalurus punctatus,in Individual Soft Mesh Bags Reduces Stress and Improves Reproductive Performance

Hormone‐induced spawning of channel catfish held communally in tanks is a reliable method to produce channel catfish, Ictalurus punctatus ♀ × blue catfish, Ictalurus furcatus ♂, F₁ hybrid catfish fry. However, mature catfish are crowded, and repeatedly handled during the process of induced ovulation. Repeated handling of gravid females is stressful and may impair ovulation, egg quality, and reproductive performance. Three trials were conducted to evaluate the effects of two methods of confining post‐hormone‐injected female channel catfish on stress response (cortisol concentrations) and reproductive performance: fish were either held individually while suspended in soft, nylon‐mesh bags or communally in a concrete tank. Percent of females ovulated to hormone treatment, relative fecundity, percent egg viability, and latency of channel catfish did not differ for fish in the two treatments. However, percent hatch and fry/kg of females was higher (P < 0.05) for fish held in bags that for fish held communally in tanks. Mean plasma cortisol response immediately prior to the first hormone injection (0 h) did not differ among fish groups in the two treatments. However, mean plasma cortisol concentrations were significantly lower (P < 0.05) for fish in the bag treatment at 16 and 36 h compared to fish held communally in tanks. Plasma estradiol levels (measure of oocyte maturation) were assessed at 0, 16, and 36 h after hormone injection; concentrations were (P < 0.05) higher at 16 h compared to 0 and 36 h; however, estradiol concentrations did not differ for fish held in the two treatments (P > 0.05). Suspending hormone‐injected broodfish individually in soft bags reduced stress response, improved egg hatching rate, and increased hybrid fry produced per kg weight of female broodfish. Using this simple technology, farmers can improve the efficiency of hatcheries producing hybrid catfish fry.     

The effects of the 1983 El Niño on Oregon's Coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) Salmon

The 1983 El Niño event off the Pacific Coast of North America resulted in increased adult mortality and decreased average size for Oregon's coho and chinook salmon. Actual return of adult coho salmon to the Oregon Production Area in 1983 was only 42% of the pre-season prediction. Coho smolts entering the ocean in the spring of 1983 also survived poorly, resulting in low adult returns again in 1984. Abundance of chinook stocks in southern Oregon was also reduced, as was abundance of Columbia River chinook stocks that show localized ocean distribution. Northerly migrating chinook stocks from the Columbia River showed little or no decline in abundance. The average weight of coho and chinook salmon landed in 1983 by Oregon's commercial troll fishery was the lowest recorded since statistics were first recorded in 1952. Comparison of the length-weight relationship for these fish indicated coho and chinook were in poorer condition in 1983 than in non-El Niño years. Because adult coho salmon returned to hatcheries at a smaller size, the fecundity (eggs per female) in 1983 was reduced from the 1978–1982 average by 24% at coastal hatcheries and by 27% at Columbia River hatcheries. The fecundity of chinook salmon was unchanged at most hatcheries.     

Stress response of juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)to chemical cues released from stressed conspecifics

The objective of this study was to determine whether exposure of rainbow trout (Oncorhynchus mykiss) to water containing a stressed trout or skin extract from stressed and non-stressed trout would elicit a stress response in conspecifics. Juvenile rainbow trout were exposed for 1 hour to water containing a stressed fish, homogenized skin extracts from a non-stressed fish, skin extract from a stressed fish and water with none of these factors. The stress response was measured over a 24-h period (1, 6, 12, 24 h after exposure). Plasma cortisol levels increased at 12 h in fish exposed to water from a stressed fish and skin extract from a stressed fish. Plasma glucose and hepatic hsp70 levels were not affected by treatments. The results suggest that rainbow trout elicit a stress response when exposed to stress-related alarm cues released from conspecifics.     

Comparison of tricaine methanesulphonate (MS222) and clove oil anaesthesia effects on the physiology of juvenile chinook salmon Oncorhynchus tshawytscha (Walbaum)

This study investigated the feasibility of using clove oil as an alternative to tricaine methanesulphonate as a fish anaesthetic, particularly in fish stress research. The physiological stress responses of juvenile chinook salmon Oncorhynchus tshawytscha (Walbaum) anaesthetized with either tricaine (50 mg L^?1) or clove oil (20 p.p.m.) were compared using unanaesthetized fish as controls. Haematocrit, serum cortisol and serum glucose concentrations, serum lysozyme activity and differential leucocyte counts were measured from blood samples collected before, during and upon recovery from anaesthesia and at specified intervals up to 72 h after recovery. Differences between the two anaesthetic groups were not significant for most of the physiological traits measured. Serum lysozyme activity of control fish, however, was significantly suppressed relative to the treated fish for 72 h after stress. Clove oil may be a safe and cost‐effective alternative to tricaine without significantly affecting study results. Furthermore, clove oil may be more practical for field‐based research, because a withdrawal period is unnecessary, and clove oil does not pose an environmental hazard.     

Relationship between dietary lipid source, oxidative stress, and the physiological response to stress in sub-yearling chinook salmon (Oncorhynchus tshawytscha)

Relationships between dietary lipid source, stress, and oxidative stress were examined in juvenile chinook salmon (Oncorhynchus tshawytscha). Four different experimental diets were used: menhaden oil (MHO; elevated 20:5n-3 and 22:6n-3), soybean oil (SBO; elevated 18:2n-6), linseed oil (LSO; elevated 18:3n-3), and a mixture of 55% linseed oil and 45% soybean oil (MIX; approximately equal levels of 18:2n-6 and 18:3n-3). Juvenile salmon (initial body weight of 16.0 g) were fed experimental diets for 12 weeks (early March to early June). At the end of feeding, fish subjected to a low-water stressor for 96 h had greater liver and brain lipid peroxidation compared to unstressed controls; peroxidation was not influenced by diet. Diet and stress affected plasma cortisol levels. Stressed fish fed SBO had the greatest cortisol concentrations, followed by MIX, MHO, and LSO (mean concentrations for the SBO and LSO diets differed significantly). The cortisol response to stress may have been influenced by the ratio of prostaglandin 1- and 2-series to prostaglandin 3-series precursor fatty acids provided by the different diets. The results of this study suggest a connection between the physiological response to stress, dietary lipid quality, and oxidative stress. This is the first evidence of such a relationship in fish. Abbreviations: AA - arachidonic acid; ACTH - adrenocorticotropin; BHT - butylated hydroxytoluene; BLPO - brain lipid peroxidation; dGLA - dihomo-γ-linolenic acid; DHA - docosahexanoic acid; EPA - eicosapentanoic acid; FER - feed efficiency ratio; FOX - ferrous oxidation-xylenol orange; GLA -γ-linolenic acid; LA - linoleic acid; LCO3 - long-chain n-3 polyunsaturated fatty acids; LLPO - liver lipid peroxidation; LN - linolenic acid; LPO - lipid peroxidation; LSO - linseed oil; MHO - menhaden oil; MIX - 55% linseed oil + 45% soybean oil; PC - plasma cortisol; PG - prostaglandin(s); PGE₂- prostaglandin E₂; PUFA - polyunsaturated fatty acid; SBO - soybean oil. This revised version was published online in July 2006 with corrections to the Cover Date.