Poor water quality suppresses the cortisol response of salmonid fish to handling and confinement

Confinement of brown trout in small troughs of static water for 1 h at a density of six fish 251⁻¹ stimulated the hypothalamic-pituitary-interrenal axis and resulted in an elevation of plasma cortisol from basal levels (less than 2 ng m1⁻¹) to about 100 ng m1⁻¹, the degree of stimulation being dependent upon water temperature. Confinement at a density of 30 fish 251⁻¹ resulted in a 50% suppression of this response. It is demonstrated that this effect is mediated by changes in water chemistry and not by crowding per se . Experimental manipulation of the water chemistry showed that reduced pH (7.1 → 6.3), elevated free CO₂ (63 → 520 μmoll⁻¹) or elevated ammonia (8 → 1300 μg 1⁻¹ as total ammonia nitrogen) had no individual effects on the interrenal response to acute confinement. Elevated ammonia in combination with reduced pH significantly increased the plasma cortisol levels in response to acute confinement, whereas a combination of reduced oxygen (100 → 20% saturation), elevated free CO₂ and elevated ammonia markedly suppressed (∼ 50%) the cortisol response of both brown trout and rainbow trout to acute confinement in a manner similar to that observed with trout at high densities. A compensatory increase in plasma cortisol levels was observed during the subsequent recovery of fish which had been confined for 1 h in water of poor quality. These findings are discussed in relation to the exposure of fish to multiple stresses and to the role of corticosteroids in the stress response.     

Dose-related effects of 17βoestradiol (E2) on liver weight, plasma E2, protein, calcium and thyroid hormone levels, and measurement of the binding of thyroid hormones to vitellogenin in rainbow trout, Salmo gairdneri Richardson

Administration of 17β-oestradiol (E₂) to rainbow trout, in the form of hydrogenated coconut oil implants produced a stable, long-term elevation in plasma E₂ levels. The elevation was doserelated (over the range 1–10mg kg-¹ body weight) both 4 and 8 weeks after implantation. Dose-related increases were also observed with respect to liver weight-body weight ratios and plasma protein levels. Plasma T₃ and total calcium levels were depressed and elevated, respectively, by E₂ treatment but the responses were not linearly related to the dose of E₂ administered; there was no significant effect of E₂ on plasma T₄ levels.
E₂ induced a shift in the binding of T₃ to plasma proteins, with T₃ binding to smaller molecular weight proteins; neither T₄ nor T₃ bound to vitellogenin which was present at high levels in the plasma of E₂-treated fish.     

Influences of photoperiod and alternate days of feeding on plasma growth hormone and thyroid hormone levels in juvenile rainbow trout

The diurnal patterns of plasma growth hormone (GH), thyroid hormone and cortisol concentrations in rainbow trout Oncorhynchus mykiss held under three photoperiod (L : D) regimes (6 : 18, 12 : 12 and 18 : 6), and fed either daily (DF) or on alternate days (ADF) with 2·0% body mass per day of a commercial trout diet were determined. The ADF groups had reduced total mass gain and specific growth rates compared with DF fish, but photoperiod had no affect on growth for either of the feeding regime groups. In the ADF groups, the mean 24 h plasma thyroxine (T₄) and triiodothyronine (T₃) concentrations were significantly lower, both on days of feeding and days of fasting, than in DF fish held under all three photoperiod regimes, but for GH, only the 18L : 6D DF group was higher than the comparable ADF groups. There were no significant differences in mean 24 h plasma cortisol concentrations of DF and ADF groups. Diurnal patterns of plasma GH, cortisol, T₄ and T₃ were found in DF fish held under all three photoperiod regimes. Increases in plasma cortisol changes were associated with the onset of the light phase; elevations in plasma GH and T₄ concentrations were more closely associated with clock time, regardless of photoperiod; increases in plasma T₃ concentrations were strongly associated with time of feeding. In ADF groups, these diurnal changes in plasma GH, T₄ and T₃ concentrations were suppressed for both the fed and fast days, and plasma cortisol concentrations were suppressed on the fasting day. The observations are discussed in terms of the proposed anabolic, catabolic and growth regulating roles of these hormones in different growth and metabolic modifying situations in teleosts.     

Studies on the relationship between osmotic or ionic regulation and thyroid gland activity in two salmonid fishes, Salmo gairdneri Richardson and Oncorhynchus kisutch Walbaum

In freshwater-acclimated rainbow trout a single intraperitoneal injection of ovine TSH significantly elevated plasma thyroxine (T₄) levels within 1 h after the injection. In seawater adapted trout the increase in T₄ after TSH-treatment was not evident until 6 h after the injection. TSH caused a transient fall in plasma Na⁺ and Cl^- between 3 h and 9 h after the injection in seawater-adapted fish and plasma Na⁺ was lowered in freshwater-adapted trout 24 h after the injection. Although there were clear histological changes in the thyroid gland of freshwater-adapted trout after TSH-injection, no such changes were evident in seawater-adapted fish.
Plasma thyroid hormone levels and thyroid histology in freshwater-adapted rainbow trout and coho salmon transferred to sea water, and seawater-adapted trout transferred to fresh water showed no consistent changes compared with controls.
The data are interpreted to indicate that although ambient salinity may have indirect effects on thyroid activity there is no direct involvement in ionic or osmotic regulation in the two species.     

Migration tendency in juvenile steelhead trout, Salmo gairdneri Richardson, injected with thyroxine and thiourea

Juvenile steelhead trout, Salmo gairdneri injected with thyroxine (T₄) near the time of seaward migration exhibited a significantly lower migration tendency than untreated controls of fish injected with saline, thiourea, or a combination of T₄ and thiourea. Fish injected with thiourea alone or in combination with T₄ prior to the time of maximum migration tendency showed enhanced migration over untreated and saline injected controls and those injected with T₄ alone. Injections of T₄ or a combination of T₄ and thiourea elevated plasma T₄ and tri-iodothyronine (T₃) concentrations, while injection of thiourea alone depressed thyroid hormone levels relative to saline-injected controls. Plasma concentrations of T₃ and T₄ returned to control levels within 10 days in all groups. We suggest that thyroid hormones are antagonistic to mechanisms underlying seaward migration of steelhead trout and that these antagonistic effects must be overcome before migration tendency is expressed.     

The role of F-series prostaglandins as reproductive priming pheromones in the brown trout

Electrophysiological studies demonstrated that the olfactory epithelium of mature male brown trout Salmo trutta parr was acutely sensitive to F-series prostaglandins (PGFs) PGF_1α and PGF_2α, with detection threshold concentrations of 10⁻¹¹ M. The olfactory epithelium was also sensitive to the PGF metabolite 15-ketoPGF_2α (threshold 10⁻⁸ m), but did not detect a further metabolite, 13,14,-dihydro-15-ketoPGF_2α Immature brown trout did not detect any of the prostaglandins tested. Exposure of mature male brown trout parr to waterborne PGF_1α and PGF_2α (concentration 10⁻⁸ m), resulted in significant increases in levels of expressible milt and the plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one, testosterone and 11-ketotestosterone. The olfactory epithelium of both immature and mature male brown trout parr was sensitive to the urine and ovarian fluid from ovulated female brown trout. Exposure of mature male brown trout parr to ovarian fluid resulted in an increase in the levels of plasma 17,20β-dihydroxy-4-pregnen-3-one whilst exposure to urine increased the levels of expressible milt. In addition, PGF_2α was found to be present within both the urine and ovarian fluid of mature female brown trout. It is suggested that the F-series prostaglandins have a role as priming pheromones in male brown trout.     

Seasonal and diurnal rhythms of thyroidal status in the rainbow trout, Salmo gairdneri Richardson

The concentrations of thyroxine (T₄) and triiodothyronine (T₃) in the blood plasma of rainbow trout ( Salmo gairdneri Richardson) at intervals throughout the year have been measured by a chemically specific gas-liquid chromatographic (GLC) method. Mean hormone levels showed a seasonal variation, maximal levels of both hormones occurring in winter and minimal concentrations in mid summer. An apparent secondary maximum in mean T₄ and T₃ concentrations was observed in spring. (T₄)/(T₃) ratios have been found to be highest in winter and lowest in summer. A radioimmunoassay procedure, validated by GLC analyses, revealed the presence of a diurnal rhythm in serum T₄ levels of trout sampled in September and in April.     

Influence of plasma lipid changes in response to 17β-oestradiol stimulation on plasma growth hormone, somatostatin, and thyroid hormone levels in immature rainbow trout

Plasma total lipids were significantly higher in 17β-oestradiol(E₂)-treated immature rainbow trout Oncorhynchus mykiss at week 4 after implantation, due to increases in polar and neutral lipids. The lipid classes responding were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, sterols and sterol esters, in a proportion that approximately reflected the increase in plasma vitellogenin (VtG) levels as measured by a non-competitive enzyme-linked immunosorbent assay (ELISA). Plasma non-esterified fatty acids and triacylglycerol were not affected by E₂ treatment. Plasma growth hormone GH levels were increased, and plasma somatostatin-14 (SRIF) levels decreased in E₂-treated fish, responses which could be secondary to elevated plasma lipid (VtG) content, although a direct E₂ action on somatotroph function is possible. Plasma T₄ concentrations were not affected by E₂ treatment, but plasma T₃ concentrations were significantly lower than in controls 1 week after implantation when plasma E₂ concentrations were the highest; this is in support of the hypothesis that E₂ has a suppressive action on T₃ production.     

Cohort sampling, anaesthesia and stocking-density effects on plasma cortisol, thyroid hormone, metabolite and ion levels in rainbow trout, Salmo gairdneri Richardson

The effect of serial removal of fish from aquaria, anaesthesia and stocking density on plasma cortisol, thyroid hormone, metabolite and ion levels was examined in rainbow trout, Salmo gairdneri , to determine the consequences of normal handling and maintenance procedures on the activity of the pituitary-adrenal and pituitary-thyroid axes in the species.
The capture and handling associated with serial removal of fish from an aquarium resulted in a rapid elevation of plasma cortisol concentrations and a slower rise in plasma glucose, Mg²⁺ and Na⁺ concentrations; plasma K.+ levels showed a transient fall shortly after commencing the sampling, followed by a significant increase.
A lethal concentration of 3-aminobenzoic acid ethyl ester (MS 222) of 125 mgl⁻¹ (but not a sublethal concentration of 62.5 ng 1⁻¹) prevented the capture stressor-associated changes in most of the measured parameters, including plasma cortisol levels, although plasma protein and ion concentrations were elevated in fish sampled after MS 222-anaesthesia.
Stocking densities from 1 to 64 fish 80 1⁻¹ aquarium did not appear to effect changes in the measured parameters, except for plasma T3/T4 ratios which decreased with increasing stocking density. The exception was found in fish which were stocked in pairs: one member of each pair had a markedly elevated plasma cortisol level and there was a high incidence of mortality, probably related to aggressive social interaction.     

Investigations on Myelination In Vitro: Regulation of 2',3'-Cyclic Nucleotide 3'-Phosphohydrolase by Thyroid Hormone in Cultures of Dissociated Brain Cells from Embryonic Mice

Abstract: The direct influence of l -3,3',5-triiodothyronine (T₃) on the development of 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37, CNPase) is demonstrated by using an in vitro culture system of dissociated embryonic mouse brain cells. Serum from a thyroidectomized calf, which contained low levels of T₃ (31 ng/100 ml), and thyroxine, T₄ (<1 μg/ml), was used in the culture medium in place of normal calf serum (T₃, 103 ng/100 ml; T₄, 5.7 μg/ml) to render the culture responsive to exogenously added T₃. The lower levels of enzyme activity observed in the presence of such a deficient medium could be restored to normal values by T₃ supplementation. Half-maximal effect was obtained with 2.5 ± 10⁻⁹ m -T₃. Three days of hormone treatment resulted in the maximal stimulation of CNPase. T₄ was less effective in inducing CNPase activity and the inactive analog of the hormone, reverse T₃ (3,3',5'-T₃) was ineffective. The morphological appearance of the cells was characterized by deformed (smaller size and less in number) reaggregates in the cultures, lacking hormone.     

Plasma and ovarian thyroxine levels in relation to sexual maturation and gestation in female Sebastes inermis

Plasma T₄ (L-thyroxine) concentrations in the viviparous rockfish Sebastes inermis showed a peak (119·3±27·8 ng ml⁻¹) during the development of embryos. Ovarian T₄ concentrations increased during vitellogenesis and final maturation and decreased during embryogenesis.However, total T₄ content within the ovary increased continuously up to the larval stages. Plasma oestradiol-17β, (E₂) concentrations peaked at the final maturation stage and then recovered to the level seen during the non-reproductive periods. Plasma testosterone (T) concentrations showed a peak (5·33±1·08 ng ml⁻¹) at the embryo stage and high levels were maintained throughout the gestation period. Plasma T₄ concentrations during the embryo stage and ovarian T₄ content during vitellogenesis were much higher than the levels reported in oviparous fishes. These data suggest that in viviparous rockfish, T₄ may be required for sustaining gestation or embryo development within the maternal body. In addition, the high content of total T₄ in the ovary implies that there probably does exist a maternal-embryo relationship during gestation as well as during vitellogenesis.     

Distribution of fingerling brook trout, Salvelinus fontinalis (Mitchill), in dissolved oxygen concentration gradients

A self-recording linear gradient tank and procedures are described in which individual brook trout fingerlings unstressed by recent transfer, unaccustomed surroundings or the presence of an observer could move freely in 16 oxygen concentration gradients within the limits of 1 and 8.9 mg O₂1⁻¹. They avoided oxygen concentrations below 4 mg 1⁻¹ most of the time and preferred 5 mg 1⁻¹ or higher more than half the time, which supports the field-derived belief that fish avoid oxygen concentrations below 5 mg l⁻¹ in the natural environment if they can.     

Catecholamine release and interrenal response of brown trout, Salmo trutta, exposed to aluminium in acidic water

Cannulated brown trout, Salmo trutta , were exposed for 36 h to synthetic water with a low calcium content of pH 5 and similar synthetic water dosed with aluminium to raise the filterable A1 from 5 to 290 μg 1⁻¹ over the 36-h period. There were no significant disturbances of plasma concentrations of glucose, cortisol or catecholamine (adrenaline and noradrenaline) in fish held in water of pH 5. The addition of aluminium to this acidic synthetic water resulted in a generalized endocrine stress response with a four-fold increase in plasma glucose concentration after 18 h and a significant increase in plasma cortisol concentration from 24 h onwards when filterable A1 exceeded 200 μg 1⁻¹. Plasma catecholamine concentration indicated an adrenergic stress response in aluminium-exposed brown trout. A transient doubling in noradrenaline after 6 h in A1 was followed by a larger increase in both plasma adrenaline and noradrenaline concentrations in fish surviving the 36-h exposure to A1.     

Seasonal changes of thyroid hormones in field-collected Atlantic cod in relation to condition indices, water temperature and photoperiod

Serum T₄ and T₃ in wild Atlantic cod Gadus morhua ranged from 1 to 12 ng ml⁻¹ and from 2 to 27 ng ml⁻¹ respectively over a 3-year period. In general, the concentrations increased from summer (T₃) or early autumn (T₄) to maxima in mid-winter and declined abruptly during spring. The T₄/T₃ monthly means were lowest in summer and highest in winter. The seasonal patterns of thyroid hormones were weakly correlated with changes in water temperature. However, both T₄ and T₃ co-varied simultaneously with photoperiod. In addition, T₃ was correlated with the hepatosomatic index and condition factor during summer and autumn. It is suggested that the seasonal changes in the release of T₄ from the thyroid were photoperioddriven, and that the course of T3 was regulated by the metabolic state of the fish during the somatic growth period.     

The effect of dissolved oxygen and salinity on the toxicity of ammonia to smolts of salmon, Salmo salar L.

The survival of Atlantic salmon smolts on exposure to constant concentrations of ammonia has been measured under laboratory conditions. At concentrations of dissolved oxygen close to the air-saturation value, the 24-h LC50 of un-ionised ammonia is 0.15 mg NH₃1⁻¹ in fresh water (hardness 264 mg 1⁻¹ as CaCO₃) and 0.3 mg NH₃1⁻¹ in 30% sea water; at concentrations of dissolved oxygen of 3.5 mg 1⁻¹ in fresh water and 3.1 mg 1⁻¹ in 30% sea water, the 24-h LC50 is 0.09 mg NH₃ 1⁻¹ and 0.12 mg NH₃ 1⁻¹ respectively; for fish acclimated for 1 day to a concentration of ammonia close to the 24-h median for un-acclimated fish, the median is increased between 38 and 79%, depending on test conditions.     

Some effects of low pH and calcium on the growth and tissue mineral content of yearling brown trout, Salmo trutta

Yearling brown trout, Salmo trutta , were exposed to low mineral content water (nominal concentrations of 20μmol 1⁻¹ magnesium, 7.7 μmol 1⁻¹ potassium, 44 μmol 1⁻¹ sodium) over a pH range of 4.0–5.2 with ambient calcium concentrations of 2.5–60 μmol 1⁻¹. All fish died at pH 4.0 and 4.2 irrespective of ambient calcium concentration and also at pH 4.4 with only 2–3 μmol 1 ⁻¹ calcium (that is calcium-free water except for that leached from the diet or excreted by the fish). Good growth rates were obtained over the remaining treatments which extended down to pH 4.4 with as little as 7 μmol 1⁻¹ calcium. When starved, weight loss was inversely correlated with pH. Effects on plasma chloride, percentage dry weight and calcium, potassium sodium, and phosphorus contents of skin, muscle and bone tissue were also investigated. These demonstrated pH effects on mineral metabolism in starved fish, but no effects were detected in fed fish.     

Scaling of oxygen consumption of Lake Magadi tilapia, a fish living at 37°C

Rates of oxygen consumption were measured in the geothermal, hot spring fish, Oreochromis alcalicus grahami by stopped flow respirometry. At 37° C, routine oxygen consumption followed the allometric relationship: V o₂=0.738 M ^0.75, where V o₂ is ml O₂ h ⁻¹ and M is body mass (g). This represents a routine metabolic rate for a 10 g fish at 37° C of 0.415 ml O₂ g⁻¹ h ⁻¹ (16.4 μmol O₂ g ⁻¹ h ⁻¹). Acutely increasing the temperature from 37 to 42° C significantly elevated the rate of O₂ consumption from 0.739 to 0.970 ml O₂ g ⁻¹ h ⁻¹ ( Q ₁₀=l.72). In the field, O. a. grahami was observed to be 'gulping' air from the surface of the water especially in hot springs that exceeded 40° C. O. a. grahami may utilize aerial respiration when O₂ requirements are high.     

Resistance to cadmium by pretreated rainbow trout alevins

A toxicity test with cadmium concentrations ranging from 0·1 to 100·0 mg Cd 1⁻¹ was used to assess the effect of cadmium pretreatment on rainbow trout ( Salmo gairdneri Richardson) alevins. The median period of survival for fish pretreated at 0·01 mg Cd 1⁻¹ was found to be increased at test concentrations up to 10mg Cd 1⁻¹ compared with alevins pretreated with dilution water. However, at concentrations above 10mg Cd 1⁻¹ pretreatment at 0·01 mg Cd 1⁻¹ reduced the median period of survival.     

In vitro evidence for the ionoregulatory role of rainbow trout mucus in acid, acid/aluminium and zinc toxicity

Rainbow trout body mucus dialysed with acidified distilled water at pH 7,5 and 3 experienced ion depletion which was greatest at pH 3 and minimal between pH 7 and 5. Mucus Na⁺ loss is exacerbated in the presence of 1 mg I⁻¹ aluminium as A1₂(SO₄), at pH 5 and 7. Al₂(SO₄), causes greater depletion of Na⁺ from mucus than A1C1₃. A lethal level of zinc (2 mg 1⁻¹) does not deplete mucus Na⁻ or K⁺, unlike a lethal level of aluminium (1 mg 1⁻¹) at pH 7. The results are discussed in terms of the ionoregulatory role of mucus in heavy metal and acid toxicity.     

Sublethal effects of the pesticide Diazinon on olfactory function in mature male Atlantic salmon parr

Diazinon, an organophosphate pesticide, had a sublethal effect on the olfactory system of mature male Atlantic salmon parr. The olfactory responses of the parr to prostaglandin F_2a (PGF_2a) were studied after exposure of the epithelium to different concentrations of Diazinon in water. Electrophysiological recordings from the epithelium indicated that the responses to this prostaglandin were significantly reduced at nominal concentrations as low as 1.0μg l⁻¹ and the threshold of detection was reduced 10-fold at 2.0 μg 1⁻¹ . Mature male salmon parr exposed for a period of 120 h to Diazinon (nominal concentrations 0.3, 0.8, 1.7, 2.7, 5.6, 13, 28 and 45 μg 1 ⁻¹) also had significantly reduced levels of the reproductive steroids, 17,20β-dihydroxy-4-pregnen-3-one, testosterone and gonadotrophin II in the blood plasma after priming with ovulated female salmon urine. Both prostaglandin F_2a and ovulated female urine are known to have important roles in synchronizing reproductive physiology and behaviour in salmonids as well as other fish species. The results are therefore discussed in relation to the possible sublethal effects of Diazinon on reproduction in the Atlantic salmon and possible effects on populations of salmonids.