Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout, Oncorhynchus mykiss (Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes)

The rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is a salmoniform fish that spawns once per year. Ripe females that had ovulated naturally, and those induced to ovulate using salmon gonadotropin-releasing hormone, were studied to determine whether follicles were forming at the time of spawning and to describe the process of folliculogenesis. After ovulation, the ovaries of postspawned rainbow trout were examined histologically, using the periodic acid-Schiff procedure, to stain basement membranes that subtend the germinal epithelium and to interpret and define the activity of the germinal epithelium. After spawning, the ovary contained a few ripe oocytes that did not ovulate, numerous primary growth oocytes including oocytes with cortical alveoli, and postovulatory follicles. The germinal epithelium was active in postspawned rainbow trout, as determined by the presence of numerous cell nests, composed of oogonia, mitotic oogonia, early diplotene oocytes, and prefollicle cells. Cell nests were separated from the stroma by a basement membrane continuous with that subtending the germinal epithelium. Furthermore, follicles containing primary growth oocytes were connected to the germinal epithelium; the basement membrane surrounding the follicle joined that of the germinal epithelium. After ovulation, the basement membrane of the postovulatory follicle was continuous with that of the germinal epithelium. We observed consistent separation of the follicle, composed of an oocyte and surrounding follicle cells, from the ovarian stroma by a basement membrane. The follicle is derived from the germinal epithelium. As with the germinal epithelium, follicle cells derived from it never contact those of the connective tissue stroma. As with epithelia, they are always separated from connective tissue by a basement membrane.     

Change of Rheoreaction and Concentration of Thyroid Hormones in Blood of Juvenile Rainbow Trout Oncorhynchus mykiss during Starvation

Journal of Ichthyology - Rheoreaction and concentration of thyroid hormones in blood of juvenile rainbow trout Oncorhynchus mykiss is studied during starvation (12 days). It is found that...     

Quantitative estimation of pituitary gonadotropin in juvenile rainbow trout with scanning cytophotometry applied to immunocytochemical preparations

A densitometrical method with computer-controlled scanning cytophotometry has been developed to quantify the amount of gonadotropin (GTH) in immunocytochemically treated paraffin sections of pituitaries of juvenile rainbow trout. Results obtained with this method totally correspond with those established with a radioimmunoassay of pooled pituitaries. Scanningcytophotometry offers the advantage that GTH-content of individual pituitaries of juvenile or small adult fish can be investigated.     

Microvascularization of the thyroid glands in larval and adult Xenopus laevis‐ histomorphology and scanning electron microscopy of vascular corrosion casts

This study demonstrates gross arterial supply, venous drainage and microvascular patterns of larval and adult thyroid glands in the African Clawed Frog, Xenopus laevis by scanning electron microscopy of vascular corrosion casts and light microscopy of stained serial tissue sections. Results confirm published findings gained by microscopical dissections with respect to gross arterial supply. However, in adult frogs one rather than two thyroid veins are found. This study reveals for the first time that bilaterally located thyroid glands in premetamorphosis have immature capillary networks, lack a clear hierarchy of blood vessels, and show many signs of sprouting angiogenesis. During metamorphic climax, blood vessels gain a clear hierarchy and capillaries form closed networks around thyroid follicles. From climax onwards, non‐sprouting angiogenesis (intussusceptive microvascular growth) becomes the prevailing mode of angiogenesis intensifying follicle capillarization. Due to narrow interfollicular spaces, thyroidal arterioles remain superficial while draining venules are located interfollicularly. In contrast with the mammalian thyroid gland where most thyroid follicles have their own capillary beds, most thyroid follicles in Xenopus share their capillary beds with neighbouring follicles. Consequently, the concept of individual morphological and functional angiofollicular units applicable to adult mammalian and human thyroid glands is not applicable to larval and adult amphibian thyroid glands.     

Effect of methyltestosterone on physiological state and rheoreaction of rainbow trout <Emphasis Type="Italic">Parasalmo mykiss</Emphasis> (=<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) under unfavorable keeping conditions

The effect of methyltestosterone given with feed during one and two months on the state of gonads, the level of thyroid, and sex steroid hormones in blood and on rheoreaction is studied in juvenile rainbow trout Parasalmo mykiss (=Oncorhynchus mykiss) raised under unfavorable conditions (tropics, Vietnam). In comparison with the control, in the experimental group, the part of sterile specimens was higher (83 vs. 35%), the part of males was lower (17 vs. 40%), while females and hermaphrodites were absent. At prolonged starvation (12 days), the experimental specimens demonstrated lower increase of the level of thyroid and sex steroid hormones in blood than that in the control specimens. Methyltestosterone modified the behavior of rainbow trout in water flow: delivery of the hormone in food during 1 month increased the part of fish moving against the flow and suppressed movement both upstream and downstream during 2 months. Thus, methyltestosterone negatively influences the physiological condition and adaptation capacity of rainbow trout.     

Effects of exercise on nitrogen excretion, carbamoyl phosphate synthetase III activity and related urea cycle enzymes in muscle and liver tissues of juvenile rainbow trout (Oncorhynchus mykiss).

The purpose of this study was to determine if carbamoyl phosphate synthetase III (CPSase III) and related urea cycle enzyme activities in skeletal muscle tissue of juvenile rainbow trout (Oncorhynchus mykiss) increase during short- or long-term exercise, in parallel with changes in whole-body urea excretion rates. Urea excretion was elevated by 65% in fish that swam at high-speed (50 cm/s) vs. low-speed (20 cm/s) over a 2-h period, with no significant changes in CPSase III, ornithine transcarbamoylase or glutamine synthetase activities in muscle tissue. Fish that swam for 4 days at high-speed had higher rates of ammonia excretion and GSase activity in muscle and liver tissue relative to low-speed swimmers. Calculations showed that 47-53% of excreted urea, theoretically could be accounted for by total muscle CPSase III activity in juvenile and adult trout. The data indicate that increases in the rate of urea excretion during short-term high intensity exercise are not linked to higher activities of urea cycle enzymes in muscle tissue, but this does not rule out the possibility of increased flux through muscle CPSase III and related enzymes. Furthermore, these results indicate that urea cycle enzyme activities in skeletal muscle tissue can account for a significant portion of total urea excretion in juvenile and adult trout.     

Does individual variation in stress responses and agonistic behavior reflect divergent stress coping strategies in juvenile rainbow trout?

Individual rainbow trout were transferred to visual isolation in experimental aquaria. As a measure of the speed of acclimation, individual food intake was quantified during the first 6 d following transfer. Following acclimation, aggression was quantified by subjecting the fish to three resident-intruder tests, with 30 d of recovery between the tests. Moreover, between the resident-intruder tests (i.e., two times) the fish were exposed to an unfamiliar environment and their cortisol response was measured. The results of this study show that individuals of juvenile rainbow trout differ distinctly in their response to changes in their environment, and that this diversity in behavior is reflected by consistent behavioral traits displayed by individual fish. These traits have proven to be consistent not only over time but also across situations, revealing two distinct behavioral profiles, in the same manner as shown in studies on proactive and reactive mammals. Our results also show that the reactivity of the hypothalamic-pituitary-interrenal (HPI) axis, when exposed to a stressor, is a consistent physiological trait in juvenile rainbow trout. We found that difference in HPI axis reactivity is linked to the different behavioral profiles. However, HPI axis reactivity could not be linked directly to the singular behavioral traits measured. In other words, we did not find that the consistent behavioral traits shown by the fish were associated with a difference in HPI axis reactivity in the same manner as the reactivity of the hypothalamic-pituitary-adrenocortical axis does in mammals. Taken together, our results show that stress coping strategies akin to what has been described as reactive and proactive stress coping in mammals appear to exist in juvenile rainbow trout.     

Apoptosis and ovarian function: novel perspectives from the teleosts

Apoptosis is a fundamental mechanism in follicular atresia and postovulatory regression in mammals, but its role in teleost ovarian function is currently unknown. This study tested the hypotheses that apoptosis mediates follicular atresia in teleosts and is inducible in vitro by incubation in serum-free conditions. Vitellogenic follicles from rainbow trout (Oncorhynchus mykiss) and goldfish (Carassius auratus) were incubated overnight in serum-free medium and examined for apoptosis by 3'-end-labeling and/or TUNEL analysis. Primary, postovulatory, and oocytectomized vitellogenic trout follicles and atretic goldfish follicles were evaluated in similar fashion. Overall, goldfish follicles had lower levels of DNA fragmentation than trout follicles. The DNA fragmentation in atretic goldfish follicles was similar to that measured in healthy vitellogenic and prematurational follicles; DNA fragmentation did not change after incubation. In the trout, postovulatory and oocytectomized vitellogenic follicles showed significantly greater in vitro susceptibility to apoptosis than intact vitellogenic follicles, whereas primary follicles were least susceptible. The TUNEL analyses revealed that in trout vitellogenic follicles, more thecal/epithelial cells than granulosa cells showed fragmented DNA in vivo, but incubation (24 h) did not result in increased apoptosis in cells of either type. These results indicate that apoptosis is involved in normal ovarian growth and postovulatory regression in teleosts, but that it does not appear to be an early event in teleost follicular atresia.     

Morphological and functional development of the thyroid tissue in rainbow trout (Oncorhynchus mykiss) embryos

The development of the thyroid tissue in rainbow trout (Oncorhynchus mykiss) embryos between 20 and 88 days postfertilization (dpf) was studied using traditional histological methods in combination with immunostaining using antibodies raised against L-thyroxine (T4) and triiodo-L-thyronine (T3). In 20 dpf embryos, the thyroid primordium appeared as a simple tube aligned with the dorsal surface of the ventral aorta. The tubular primordium becomes progressively bifurcated at each end and follicles are formed by pinching off balls of cells from the tips of the bifurcations. The secretory activity of the thyroid tissue appears first as a synthesis phase, evident at 30 dpf, characterized by T4 and T3 immunostaining present only in the follicle lumen. A later hormone release or secretory phase was first evident for T4 immunostaining at 43 dpf and for T3 immunostaining at 46 dpf and was characterized by the presence of immunostaining both within the follicle lumen and also in the cytoplasm of some (but not all) thyrocytes. This stage was also coincident with a marked increase in the number of pituitary thyrotrophs. The proportion of embryos exhibiting immunostained thyrocytes increased progressively from 43 to 52 dpf, at which stage all embryos had T4- and T3-immunostained thyrocytes.     

Magnetic field perception in the Rainbow Trout, <Emphasis Type="Italic">Oncorhynchus</Emphasis> <Emphasis Type="Italic">mykiss</Emphasis>

In this study, we present evidence for the perception of different magnetic field parameters in a facultative anadromous fish species of the family Salmonidae. Magnetic field perception of the rainbow trout, Oncorhynchus mykiss, was demonstrated with a heartbeat conditioning test. The electrocardiogram was measured with subcutaneously inserted silver wire electrodes in freely swimming fish. We demonstrate a conditioned response (i.e. a significant longer interval between two heartbeats) to an intensity/inclination shift for three adult and two juvenile rainbow trouts. Moreover, a conditioned response to a 90° direction shift was demonstrated for three adult and two juvenile trouts. These findings support the hypothesis that the rainbow trout is able to perceive different magnetic field parameters. Furthermore, the study demonstrates magnetosensation in different developmental stages in the rainbow trout, i.e. juvenile and adult fish.     

Induction, isolation and a characterization of the lipid content of plasma vitellogenin from two Salmo species: rainbow trout (Salmo gairdneri) and sea trout (Salmo trutta)

Vitellogenin synthesis is induced in juvenile rainbow trout (Salmo gairdneri) and juvenile sea trout (Salmo trutta) by estradiol-17 beta. A purification procedure for vitellogenin from trout plasma by precipitation with MgCl2-EDTA and subsequent anion exchange chromatography on DEAE-Sephacel is described. The total lipid contents of purified rainbow trout and sea trout vitellogenins are 18 and 19%, respectively. Approximately 2/3 of the lipids are phospholipids, while the remainder consists of triglycerides and cholesterol. Phosphorus determinations on delipidated vitellogenin yield a phosphorus content of 0.63% in rainbow trout and 0.58% in sea trout vitellogenin. Native (dimeric) vitellogenins from rainbow trout and sea trout both have an apparent molecular weight of 440,000, when estimated by gel filtration on Sepharose 6B.     

Diurnal rhythms of plasma growth hormone,somatostatin, thyroid hormones,cortisol and glucose concentrations in rainbow trout,Oncorhynchus mykiss,during progressive food deprivation

Abstract

The diurnal patterns of changes in plasma cortisol, growth hormone (GH), somatostatin‐14 (SRIF), thyroid hormones (L‐thyroxine, T₄ and triiodo‐L‐thyronine, T₃) and glucose were investigated in rainbow trout, Oncorhynchus mykiss, both during single meal‐feeding and during a progressive fast of 13 weeks. All measured variables exhibited a diurnal pattern in fed rainbow trout, most of which appeared to be correlated with the time of feeding (30–60 min after the onset of light), while additional changes, associated with the scotophase were also found for cortisol. Although fasting had no affect on mean daily plasma cortisol or SRIF concentrations, there was a progressive increase in mean daily plasma GH concentrations and a progressive decrease in mean daily plasma thyroid hormone and glucose concentrations associated with fasting. However, for GH, significant changes were not evident until week 10 of the fast. In addition, fasting appeared to phase‐shift the diurnal patterns of plasma GH, cortisol and glucose concentrations; the consequence of such a shift is that conclusions as to the effects of fasting, if based on a single time of sampling, may be flawed.     

Effect of Diet Change on Rheoreaction in Young Rainbow Trout Oncorhynchus mykiss

Journal of Ichthyology - The motivational component of rheoreaction has been determined in 4-month-old juvenile rainbow trout Oncorhynchus mykiss on different diets. It is shown that the diet...     

Thyroglobulin may affect telomerase activity in thyroid follicular cells

Telomerase (TA) activity is known to be present in malignant tumor cells, but not in most somatic differentiated cells. TA shows relatively high activity in thyroid cancer cells, but reports vary. This fact prompted us to elucidate whether cell component inhibitors of TA in the thyroid follicles can modulate its activity. The activity of TA extracted from Hela cells was inhibited by mixing with the supernatant fraction of human thyroid tissue extract. To examine the effect of iodine, thyroid hormones (?-T3 and ?-T4) and human thyroglobulin (hTg) contained in the thyroid follicles, ?-T3, ?-T4 and hTg were added to the TRAP assay system in vitro, using TA from Hela cells. Iodine, ?-T3 and ?-T4 did not affect TA activity, but hTg inhibited the TA activity in a dose-dependent manner (IC₅₀ of hTg: ca 0.45 μM: inhibiting concentration of hTg was from 0.15 μM to 3.0 μM). The hTg inhibition was not evident in the RT-PCR system, suggesting no effect of hTg on Taq DNA polymerase activity. The hTg inhibition of TA activity was attenuated by dNTP but not significantly by TS primer. These data suggest that hTg contained in thyroid follicular cells of various thyroid diseases may affect the TA activity measured in biopsied thyroid specimens, and that the reduction of the TA activity by hTg may induce slow progression and growth, and low grade malignancy of thyroid cancer, particularly differentiated carcinoma.     

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.     

Thyroxine induces transitions in red muscle kinetics and steady swimming kinematics in rainbow trout (Oncorhynchus mykiss)

During normal development, rainbow trout undergo a shift in red muscle contraction kinetics and swimming kinematics. Young trout parr have faster muscle kinetics and faster tailbeat frequency during swimming than older, larger juvenile trout. In this study, the thyroid hormone thyroxine (T(4)) was used to induce these changes in trout parr. This allowed a comparison of swimming kinematics, through the use of video analysis and electromyography, and red muscle contractile properties, through the use of in vitro muscle preparations, between natural parr and same-sized induced juveniles. The red muscle of natural parr has faster contractile properties than induced juveniles, including faster twitch time and a faster maximum shortening velocity (V(max)). Further, natural parr swim with faster tailbeat frequencies than induced juveniles. The results suggest that the natural shift in red muscle contraction kinetics observed during parr-smolt transfomation in trout directly affects swimming behavior in these fish. Also, thyroid hormones appear to induce a shift towards slower isoforms of the muscle protein myosin heavy chain (MHC), a result distinct from work on rats where thyroid hormones induce shifts towards faster forms of MHC. J. Exp. Zool. 290:115-124, 2001.     

Comparative susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis, the cause of salmonid whirling disease.

The susceptibility of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta to Myxobolus cerebralis, the cause of salmonid whirling disease, was assessed following dosed exposures to the infectious stages (triactinomyxons). Parallel groups of age-matched brown trout and rainbow trout were exposed to 10, 100, 1000 or 10,000 triactinomyxons per fish for 2 h and then placed in aquaria receiving single pass 15 degrees C well water. Severity of infection was evaluated by presence of clinical signs (whirling and/or black tail), prevalence of infection, severity of microscopic lesions, and spore counts 5 mo after exposure. Clinical signs of whirling disease, including a darkened caudal region (black tail) and radical tail chasing swimming (whirling), occurred first among rainbow trout at the highest dose at 6 to 7 wk post exposure. Black tail and whirling occurred among rainbow trout receiving 1000 and 100 triactinomyxons per fish at 8 to 9 wk post exposure. Only 1 of 20 fish had a black tail among rainbow trout receiving 10 triactinomyxons per fish, although 30% of the fish were infected at 5 mo post exposure. Black tails were observed in brown trout at 1000 and 10,000 triactinomyxons per fish beginning at 11 and 7 wk post exposure, respectively. There was no evidence of the tail chasing swimming (whirling) in any group of brown trout. The prevalence of infection, spore numbers, and severity of microscopic lesions due to M. cerebralis among brown trout were less at each exposure dose when compared to rainbow trout. Infections were found among rainbow trout at all doses of exposure but only among brown trout exposed to doses of 100 triactinomyxons per fish or greater. Risk of infection analyses showed that rainbow trout were more apt to be infected at each exposure dose than brown trout. Spore counts reached 1.7 x 10(6) per head among rainbow trout at the highest dose of exposure compared to 1.7 x 10(4) at the same exposure dose among brown trout. Spore numbers increased with dose of exposure in rainbow trout but not in brown trout. As microscopic lesion scores increased from mild to moderate, spore numbers increased in rainbow trout but not brown trout. The mechanisms by which brown trout resist infections with M. cerebralis were not determined. Cellular immune functions, including those of eosinophilic granular leukocytes that were more prominent in brown trout than rainbow trout, may be involved.