Physiological responses in Nile tilapia exposed to different photoperiod regimes

After conditioning Nile tilapia Oreochromis niloticus for 2 weeks, the photoperiod regime of 12 tanks of fish was changed to a 6L : 6D photoperiod while 12 further tanks were retained on the conditioning photoperiod regime (12L : 12D). Blood samples were collected 3 days (first sampling) and 3 months (second sampling) after changing the photoperiod regime. Blood was collected at 6 h intervals from both photoperiod regimes (1000, 1600, 2200 and 0400 hours). At the first sampling time, fish in the 6L : 6D had significantly higher cortisol both in the light and dark phases than levels in fish in the 12L : 12D photoperiod. At the second sampling time, the levels were significantly higher only in the light phase. The levels of cortisol, glucose and Cl⁻ in fish exposed to the 6L : 6D photoperiod, however, were far lower than those of acute stress‐induced levels observed in fish exposed to a stress experiment. Furthermore, there were no significant differences in overall values of all the variables between the photoperiod regimes at the second sampling time. This indicated that the fish exposed to the 6L : 6D photoperiod were not chronically stressed. Significantly higher blood lymphocyte counts were observed in fish exposed to the 6L : 6D compared to those of the 12L : 12D photoperiod during the light phase at the second sampling time. Other variables (glucose, Cl⁻, haematocrit and neutrophil) did not show a significant difference between the treatments at either sampling time. These results demonstrated that the artificial photoperiod regime did not cause a significant acute or chronic stress response in Nile tilapia.     

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.     

Effect of rearing density on thyroid and interrenal gland activity and plasma and hepatic metabolite levels in rainbow trout, Salmo gairdneri Richardson

There were significant inverse correlations between rearing density of rainbow trout, Salmo gairdneri Richardson, and final body weight, plasma L-thyroxine (T₄), trüodo-L-tryronine (T₃), cortisol and protein concentrations, plasma T₄/T₃ ratios and thyroid epithelial cell height. In addition, hepatosomatic indices and plasma free fatty acid concentrations were higher in fish reared at low (134 g 1⁻¹) density compared with groups reared at medium (210g1⁻¹) or high density (299g 1⁻¹), and the post-feeding (3.5-4h) elevation in plasma glucose and triglyceride levels evident in trout maintained at low rearing density was not found in those fish reared at higher densities. There were no significant effects of rearing density on hematocrit, carcass composition, hepatic glycogen and lipid levels and interregnal nucleus size.     

Cortisol and thyroid hormone responses to acid stress in the brown trout, Salmo trutta L.

Individual cannulated brown trout monitored during exposure to acidic water showed increased plasma cortisol after 3 h at pH 4.0 with low (0.05 mm) or high (2.8 mm) calcium (Ca) content, and after 2 days in acidic water with a high Ca content. Most fish did not survive for 2 days in acidic water with a low Ca content. Non-cannulated fish showed a similar increase in mean plasma cortisol after 2 days in high-Ca acidic water (pH 4.0–4.6), but not in acidic water of a low Ca content. After 7 days of exposure to acidic water, plasma cortisol appeared to recover when there was a high Ca content but increased 20-fold when Ca content was low. In cannulated fish severe acid stress resulted in a marked and rapid thyroid response. Plasma thyroxine (T₄) was elevated after 3 h exposure to acidic water of both low and high Ca content and remained elevated for 2 days of acid exposure with high Ca. In non-cannulated fish an increase in mean T₄ was apparent only after 7 days in low-Ca acidic water. Plasma triiodothyronine (T₃) levels were not significantly altered by any of the acid regimes. Plasma glucose of cannulated fish was elevated within 3 h of acid-exposure and remained elevated after 2 days in high-Ca acidic water.     

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.     

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.     

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.     

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.     

Endocrine, osmoregulatory, respiratory and haematological parameters in flounder exposed to the water soluble fraction of crude oil

Flounders Pleuronectes flesus with an implanted vascular catheter were exposed to a 50% dilution of the water soluble fraction (WSF) of Omani crude oil (c. 6ppm total aromatic hydrocarbons) and serial blood samples taken to determine their endocrine status (cortisol, catecholamines and thyroid hormones) and the resultant and/or causal physiological (haematological, ionoregulatory and respiratory) disturbances. This resulted in a progressive increase in plasma cortisol concentrations from 3 h onwards (rising from 18 to 51 ng ml⁻¹ after 48-h exposure), and increased plasma glucose concentrations indicating a generalized stress response. Plasma T3 and T4 concentrations of both control and WSF-exposed groups declined progressively over the experimental period; exposure to the WSF of crude oil further depressed plasma T4 concentrations but not plasma T₃ concentrations relative to those of control fish. Plasma osmolality and sodium and chloride concentrations were stable in WSF-exposed fish, however, plasma potassium concentrations were increased significantly at the 24-and 48-h sampling points. The most profound physiological disturbance in WSF-exposed fish was a dramatic decline in blood oxygen content (CvO₂) (from 2–8 to 0–8 ml 100 ml⁻¹ after 48-h exposure), which is likely to be the cause of the increased plasma noradrenaline concentrations from 3 h onwards. Increased noradrenaline is likely in turn to have been responsible for the significant increase in blood haematocrit and blood haemoglobin at the 3-h sampling point, although the dominant effect in the longer-term was a significant decline in both of these haematological parameters.     

Changes in plasma thyroid hormone levels in pink salmon, Oncorhynchus gorbuscha, during their spawning migration in the Fraser River (Canada)

Plasma thyroid hormone levels were measured in pink salmon, Oncorhynchus gorbuscha , during their spawning migration in the Fraser River, British Columbia. The plasma levels of both l-thyroxine (T₄) and triiodo-l-thyronine (T₃) were significantly higher in males than in females. In both sexes the hormone levels were maintained, or increased somewhat, during the early stages of migration, but fell thereafter. In females the plasma T₄ and T₃ levels of salmon collected on the spawning grounds were at or below detectable levels of the assays. The changes in thyroid hormone levels are correlated with changes in plasma insulin, gonadotropin, gonadal steroid hormones, cortisol and vitellogenin levels measured in the same specimens.     

Characterization of the cortisol response following an acute challenge with lipopolysaccharide in yellow perch and the influence of rearing density

Two experiments were performed to characterize the corticosteroid response of yellow perch Perca flavescens following an intraperitoneal injection of lipopolysaccharide (LPS) and determine if sustained differences in rearing density alter this response. In the first experiment, yellow perch were injected with LPS (3 mg kg⁻¹), saline, or handled without receiving any injection. Concentrations of cortisol in plasma were elevated in all groups relative to non‐disturbed fish at 1·5 and 3 h after handling but by 6 h after injection the mean concentration of cortisol in plasma from LPS‐injected yellow perch were three to five times higher than fish before injection and significantly larger than groups of fish not treated with LPS. In the second test, yellow perch were held at different rearing densities (9 v . 18-19 kg m⁻³) for 3, 7 and 14 days before injection with LPS (3 mg kg⁻¹). The cortisol response of yellow perch following LPS injection of fish held for 14 days at high density was significantly lower than that of fish held at the low density for the same duration. Additionally a trend of a decreased cortisol response to LPS injection as duration of holding increased was observed among fish held at high density relative to fish held at low density. These data illustrate that the corticosteroid response of yellow perch following LPS injection is distinct from handling alone and that the magnitude of the response is impacted by rearing density.     

Influence of Photoperiod, Daylength, and Feeding Schedule on Tadpole Growth and Development

The metamorphic rate of Rana pipiens tadpoles was studied under different photoperiods, daylengths, and feeding schedules. Tail resorption and hindlimb growth and development induced by immersion in 30 μg/l thyroxine (T₄) were accelerated under longer photoperiods and continuous light when 6L: 18D, 12L: 12D, 18L: 6D, and 24L regimes were compared. Constant light exposure did not produce faster development than an 18 hr photoperiod, and initially was less effective. The rate of spontaneous and T₄-induced metamorphosis was greater the shorter the day on 9L:9D, 12L: 12D, or 15L: 15D cycles, although all groups received the same overall amount of light, but in different dosages. When feeding schedule but not the LD cycle was varied, groups of tadpoles fed on 18, 24, or 30 hr regimes showed no differences in growth and development rate on 19L: 5D, and only random variations under continuous light. Differences in metamorphic rate on 18, 24, or 30 hr days are not due to the feeding schedules, but to the LD cycles. From these experiments we conclude that illumination, particularly the length and frequency of the photoperiod, affects the utilization of T₄. Development rates independent of the total amount of illumination, but related to daylength and light schedule, suggest interaction of light with an endogenous timing mechanism.     

Thyroid Hormone Replacement Restores Circulating Enkephalin Concentrations in Hypophysectomized Fetal Sheep

Abstract: We have investigated the effects of fetal hypophysectomy (HX) with or without thyroxine (T₄) replacement on the plasma concentrations of free methionine-enkephalin (free Met-Enk), noradrenaline, and adrenaline in late gestation sheep fetus. Plasma adrenaline concentrations were significantly higher in intact fetal sheep (1.05 ± 0.12 pmol/L) between 125 and 140 days of gestation when compared with the HX + saline (0.64 ± 0.10 pmol/L) and HX + T₄ (0.61 ± 0.08 pmol/L) groups. During the first 15 days of the T₄ or saline infusion, the plasma concentrations of free Met-Enk were significantly higher in the HX + T₄ group (392 ± 40 pmol/L) than in the HX + saline group (299 ± 43 pmol/L). At this stage of gestation, however, circulating concentrations of free Met-Enk were significantly higher in intact fetal sheep (556 ± 51 pmol/L) than in either of the HX groups. Between 125 and 140 days of gestation, plasma free Met-Enk concentrations were similar and significantly higher in the intact and HX + T₄ groups than those measured in the HX + saline fetal sheep. We conclude that the decrease in circulating free Met-Enk concentrations after removal of the fetal pituitary is primarily a consequence of functional athyroidism.     

Thyroid hormone levels in Atlantic salmon (Salmo salar) during the return migration from the ocean to spawn

Serum thyroid hormone levels were determined in adult Atlantic salmon ( Salmo salar ) of both sexes caught in the ocean and at a sequence of locations on their return migration to spawn. Tri-iodothyronine (T₃) levels were greatest in fish caught in coastal or estuarine waters or in a river near head-of-tide. T₃ levels were lower in fish caught in rivers throughout the angling season and lowest in those captured entering a tributary near spawning. Thyroxine (T₄) levels were lowest in immature fish captured in the ocean in winter but raised in fish captured in spring; many of the latter group showed endocrine evidence of their becoming sexually mature. T₄ levels were greatest in fish captured in coastal waters and progressively lower in fish captured in an estuary, near head-of-tide and in rivers. T₄ levels in fish captured at tributary entry near spawning exceeded those in fish caught in rivers earlier in the year. In general, these data support the hypothesis that motor activity level in migrant fish is a determinant of thyroid status.     

Seasonal changes in thyroidal status in the plaice, Pleuronectes platessa L.

A chemically specific analysis for plasma thyroid hormones has been used to disclose a seasonal bimodality in the concentrations of thyroxine (T₄) and triiodothyronine (T₃) in the plaice; maxima in both hormone levels occur in winter and in summer. The ratio of T₄ concentrations to T₃ varies seasonally being at a minimum in summer. A highly significant correlation of T₄ plasma levels with the landings per unit fishing effort for the same area has been observed.     

Patterns of oocyte growth, vitellogenin and gonadal steroid concentrations in greenback flounder

The pattern of oocyte development in association with changes of plasma concentrations of vitellogenin (Vtg), 17β‐oestradiol (E₂) and testosterone (T) was investigated in maturing female greenback flounder Rhombosolea tapirina over the first part of a reproductive season (February to June). Examination of oocyte size‐frequency distributions showed that the oocyte developmental pattern in R. tapirina is multiple group synchrony, and that reproductively mature fish were present at all sampling times. There were no significant temporal variations in the gonado‐somatic index ( I _G), hepato‐somatic index ( I _H), or plasma concentrations of Vtg, E₂ and T during the sampling period, which indicates that reproductive development is not synchronized within the population. Significant increases in I _G, I _H and plasma concentrations of Vtg, E₂ and T, however, were observed in vitellogenic fish, and in fish undergoing final maturation. A positive relationship was also found between the growth of oocytes and plasma concentrations of Vtg, E₂ and T, although the patterns of increase were different for each variable. Plasma concentrations of Vtg and E₂ rose steadily across oocyte sizes from 100 to 450 μm, but the rate of increase of plasma E₂ was slower than that of Vtg, and both reached a saturated concentration at oocyte sizes of c . 450 μm. In contrast, plasma concentrations of T showed no marked increase until oocytes grew beyond 400 μm.     

Long-term ammonia exposure of turbot: effects on plasma parameters

Turbot juveniles were exposed to four ammonia concentrations [0·17 (L), 0·34 (M), 0·73 (MH) and 0·88 (H) mg l⁻¹ NH₃-N] for different exposure durations (28 days minimum to 84 days). Their physiological status and growth performances were compared to a control group [0·004 (C) mg l⁻¹ NH₃-N]. No growth was observed in the H group, and by day 57, mass increase in the MH group was only 15% of that in group C. During the first month growth in the L group was similar to that in control group while it was lower (33%) in the M group; afterwards the L and M groups had a similar growth (half that of controls). Accumulation of total ammonia nitrogen (TA-N) in plasma was dependent on ambient ammonia concentrations. Plasma urea levels in ammonia-exposed fish were lower, similar or greater than in controls (depending on ammonia concentration or exposure duration). Osmolarity, Cl^– and Na⁺ plasma concentrations were stable in the L and M groups. The increases in Na⁺, Cl^–, K⁺ and total Ca concentrations observed by the end of the experiment in the H and MH groups suggest that fish failed to adapt. There was an initial rise in plasma cortisol in all ammonia-exposed groups followed by a return to basal level (1·7–4 ng ml⁻¹) in the L and M groups. In group MH, plasma cortisol peaked at 42 ng ml⁻¹ by day 14, and after a decline at c . 1 month (14 ng ml⁻¹), it rose again.     

Changes in thyroid function and gonadotrophin activity during sexual development in ducks Anas sp. (Aves: Anatidae)

Age-related changes in plasma iodohormone concentrations in male and female Aylesbury and Khaki Campbell ducklings were determined between the second week after hatching and sexual maturity.
In both sexes and strains the concentration of total thyroxine (T₄) and the free thyroxine index (FT₄1) were low during the first 6–8 weeks after hatching. A marked increase in the T₄ and FT₄1 occurred when the ducklings were nine weeks old; T₄ progressively increased over the following four weeks and remained high thereafter. The T₄ concentration in both sexes was directly related to age.
Concentrations of total tri-iodothyronine (T₃) were more variable than T₄ but were highest before sexual maturation and inversely age-related. An age-related decline in free tri-iodothyronine index (FT₃1) was observed during the first nine weeks.
The possibility that these maturational changes in thyroid function may reflect changes in gonadal activity was assessed by measuring the concentration of luteinizing hormone (LH) in the same plasma samples. Although plasma LH increased with age, in all cases the increase occurred after changes in the thyroid hormones were observed. Moreover, the maturational pattern of LH was related to sex and strain whereas thyroid function was unaffected by sex or strain.
These results demonstrate reciprocal changes in plasma T₃ and T₄ levels in ducks during sexual development, although the stimuli responsible and physiological significance are uncertain.     

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.     

Individual feeding success of juvenile perch is consistent over time in aquaria and under farming conditions

Juvenile (0+ year) perch Perca fluviatilis , held in tanks (1 m³) for 8 months under constant temperature (17° C) and light (12L : 12D) conditions, were weighed monthly. Individually marked fish from the tanks were placed in aquaria in groups of four and tested for feeding success, assessed as individual share of a group meal in three identical short‐term aquarium experiments separated in time (January, May and June). The groups consisted of the same individuals in each of the three experiments. In tanks, growth (thermal growth coefficient, G _T) was used as a measurement of feeding success. Individual G _T in tanks was consistent over time, and individual share of a group meal in aquaria was consistent between consecutive months. There was no connection between individual feeding success in aquaria and G _T in tanks in May and June, and in January the factors were negatively correlated. The condition factor at the start of aquarium experiments and feeding success in aquaria were negatively correlated in June and tended to be so also in May. Boldness in aquaria was negatively correlated with growth in tanks. Thus, individuals that were successful in one environment seemed to be less successful in the other. There was a seasonal change in G _T, with an increase from March to April and from April to June despite constant day length and temperature.