Carl B. Schreck

Changes in plasma cortisol during stress and smoltification in Coho Salmon, Oncorhynchus kisutch☆

The cortisol stress response in juvenile coho salmon, Oncorhynchus kisutch, considered as the difference between resting and peak poststress cortisol levels, increased from 80 ng/ml in March to 166 ng/ml in July, the period when smoltification normally occurs. Resting plasma cortisol levels also continually increased from 4 ng/ml in March to a maximum of 39 ng/ml in May, but then declined again to 3 ng/ml in July. The results indicate that there is an increased interrenal responsiveness to stress during the period of smoltification in coho salmon.

Electrofishing Mark–Recapture and Depletion Methodologies Evoke Behavioral and Physiological Changes in Cutthroat Trout

Abstract We examined the behavioral and physiological responses of wild and hatchery-reared cutthroat trout Oncorhynchus clarki subjected to a single electroshock, electroshock plus marking, and multiple electroshocks in natural and artificial streams. In a natural stream, cutthroat trout released after capture by electrofishing and marking showed distinct behavioral changes: fish immediately sought cover, remained relatively inactive, did not feed, and were easily approached by a diver. An average of 3–4 h was required for 50% of the fish to return to a seemingly normal mode of behavior, although responses varied widely among collection sites. Using the depletion method, we observed little change in normal behavior offish remaining in the stream section (i.e., uncaptured fish) after successive passes with electrofishing gear. In an artificial stream, hatchery-reared and wild cutthroat trout immediately decreased their rates of feeding and aggression after they were electroshocked and marked. Hatchery fis...

Stress and cortisol treatment changed affinity and number of glucocorticoid receptors in leukocytes and gill of coho salmon

To determine whether glucocorticoid receptors were altered during observed changes in immune function after stress or cortisol treatment, we conducted a series of experiments in which juvenile coho salmon (Oncorhynchus kisutch) were acutely or chronically stressed or fed a single meal containing cortisol. We then determined glucocorticoid receptor (GR) binding in cell-free gill preparations and whole leukocytes from spleen and anterior kidney using the synthetic hormone triamcinolone acetonide as radioligand. The affinities of GR were consistently lower in all tissues from chronically stressed fish than in tissues from controls; however, numbers of GR increased in whole leukocytes and decreased in gill. Acute stress had no affect on GR in gill and did not affect the affinity of GR in anterior kidney leukocytes, but did increase the number of GR in those leukocytes. Acute stress reduced affinity and increased numbers of GR in splenic leukocytes, suggesting heterogeneity of response to stress. Feeding cortisol to fish resulted in changes in GR from gill similar to those caused by chronic stress. Incubating leukocytes in cortisol for 3 or 24 h prior to assaying GR resulted in increased number and decreased affinity of GR in anterior kidney leukocytes, but had no effect on cells from spleen.

Physiological Effects on Coho Salmon and Steelhead of Exposure to Suspended Solids

Abstract Yearling coho salmon Oncorhynchus kisutch and steelhead Salmo gairdneri were exposed to high (2–3 g/L) or low (0.4–0.6 g/L) concentrations of three kinds of suspended solids (topsoil, kaolin clay, and volcanic ash) as long as 7–8 d. Such exposure did not cause mortality, but plasma cortisol concentrations were temporarily elevated in both species after exposure to 2–3 g/L of suspended topsoil, indicating that such exposure may have been stressful to the fish. Feeding rates of both species were reduced at high exposure concentrations. Exposure of yearling steelhead for 2 d to high or low concentrations of suspended topsoil, kaolin clay, or volcanic ash induced similar elevations of plasma cortisol levels, and, in groups exposed to high concentrations, blood hematocrits were increased. Osmoregulatory performance in fresh water and after transfer to 26‰ seawater was unaffected, and gill tissue appeared normal, after exposure to suspended solids. Exposure of yearling steelhead to high concentrations ...

Glucocorticoid receptors in leukocytes and gill of juvenile coho salmon (Oncorhynchus kisutch)

We demonstrated that cytosol from the gill of coho salmon (Oncorhynchus kisutch) had saturable, high affinity, low capacity binding to radiolabeled [3H]cortisol (Kd = 2.24 +/- 0.28 nM, mean +/- 1 SE; Nmax = 41.4 +/- 7.4 fmol/mg protein) and radiolabeled [3H]triamcinolone acetonide (TA; Kd = 0.38 +/- 0.03 nM, Nmax = 37.8 +/- 4.9 fmol/mg protein). Similarly, TA bound to cytosolic fractions of leukocytes harvested from spleen (Kd = 0.32 +/- 0.03 nM, Nmax = 8.3 +/- 2.0 fmol/mg protein) and anterior kidney (Kd = 0.37 +/- 0.03 nM, Nmax = 30.2 +/- 5.2 fmol/mg protein) and to whole leukocytes from spleen (Kd = 0.30 +/- 0.04 nM, Nmax = 445 +/- 57 sites/cell) and anterior kidney (Kd = 0.40 +/- 0.04 nM, Nmax = 1198 +/- 180 sites/cell). The competition hierarchies of steroid competitors were the same for both ligands and all tissues (TA greater than cortisol greater than 17 alpha-hydroxyprogesterone greater than cortisone greater than aldosterone greater than testosterone). The differences in ligand binding in leukocytes from spleen and anterior kidney are consistent with previously reported organ-dependent sensitivity of leukocytes to cortisol.

Notes: Comparison of Predator Avoidance Capabilities with Corticosteroid Levels Induced by Stress in Juvenile Coho Salmon

Abstract The relationship between predator avoidance deficits induced by a simple handling stress and the level of plasma corticosteroids was determined for juvenile coho salmon Oncorhynchus kisutch. Groups of fish were held out of water for 1 min, then allowed to recover from this stress for 1, 90, or 240 min. After each recovery period, some unstressed and stressed fish were sampled for plasma cortisol, and others were subjected to predation by lingcod Ophiodon elongatus. Levels of corticosteroids in stressed fish remained high throughout the 240-min period of recovery, but predator avoidance returned to control levels in less than 90 min. Results suggest that juvenile coho salmon quickly recover basic survival skills of predator avoidance after mild stress, even though cortisol levels continue to indicate a stressed condition.

The production of functional sex-reversed male rainbow trout with 17α-methyltestosterone and 11 β-hydroxyandrostenedione☆

Abstract The sex of gynogenetic rainbow trout was reversed to produce XX males by using two steroids, 17α-methyltestosterone (MT) and 11 β-hydroxyandrostenedione (OHA). Fish were exposed to either single or multiple doses of steroids during various times around the period of hatching to determine the labile period for effective sex reversal. Steroids were administered either by immersion (400 μg/ 1 for 2 h) or a combination of immersion plus feeding (3 mg/kg diet for 60 days) to determine if males with intact sperm ducts could be produced. Immersion in MT resulted in varying degrees of masculinization while immersion plus feeding produced nearly 100% male populations. The most effective period for steroid immersion was 1 week after the time when one-half of the fish had hatched. Multiple immersions in MT failed to increase masculinizing effects. Immersion in OHA caused only low rates of masculinization, while immersion plus feeding resulted in 70% male populations. Males produced through both immersion and feeding of MT generally did not develop sperm ducts; whereas animals treated by immersion alone in MT, or those produced with OHA, tended to be functional. Although final yields for sex-reversed males following gynogenesis were low, 1.5 and 1.6% for the two groups respectively, cryopreserved semen from these males can be used to produce all-female offspring for years. Cryopreserved semen from functional males in this study produced 100% female populations.

Plasma prolactin and cortisol concentrations of stressed coho salmon, Oncorhynchus kisutch, in fresh water or salt water ☆

Juvenile coho salmon, Oncorhynchus kisutch, adapted to fresh water or seawater were either acutely handled or continuously stressed by severe confinement. Chronic stress, independent of external salinity, caused a gradual increase in the concentration of circulating prolactin that persisted for 1 to 5 days but lagged behind the cortisol response which peaked much more rapidly and remained elevated. Acutely stressed fish showed a rapid, more transient increase in plasma cortisol titer with no apparent effect on prolactin. Confinement appeared to be more stressful to fish in salt water than to those in fresh water, as judged by their sodium regulatory ability, hormone profiles, and mortality. Stress always elevated plasma prolactin concentrations, regardless of medium or developmental stage.

Changes in Numbers of Leukocytes in Immune Organs of Juvenile Coho Salmon after Acute Stress or Cortisol Treatment

Abstract We examined the effects of acute stress and cortisol treatment on the number of leukocytes (normalized for fish body weight) in the blood, thymus, spleen, and anterior kidney of juvenile coho salmon Oncorhynchus kisutch. In acutely stressed or cortisol-fed fish, the numbers of leukocytes increased significantly in the thymus and anterior kidney, and decreased significantly in blood and spleen within 1 d after treatment. Numbers of cells in the anterior kidney, blood, and spleen returned to control levels by 3 d after treatment, but cell numbers in the thymus remained significantly greater than control values until 3–7 d after acute stress. Although dietary cortisol resulted in increased plasma cortisol titers and caused the same changes in leukocyte distribution as those caused by acute stress, the magnitude or duration of elevated cortisol levels and leukocyte numbers were not correlated. These results suggest that, although increased plasma cortisol titers induced by stress may be involved in t...

Regulation of the interrenal of fishes: non-classical control mechanisms

The regulation of the interrenal of teleostean fishes is reviewed from the perspective of non-classical control mechanisms and new evidence is presented suggesting gonadotropic control of the interrenal. Cortisol secretion by the interrenal, in addition to regulation by ACTH, appears to be mediated by other hormones. Physiologically relevant, direct control of interrenal function by hydromineral factors is unclear.In vitro experiments with interrenals of coho salmon (Oncorhynchus kisutch) indicate that salmon gonadotropin is extremely corticotropic and both ACTH and gonadotropin stimulate the secretion of large quantities of androstenedione from the interrenal.