The interrelationship of cortisol, gill (Na + K) ATPase, and homeostasis during the Parr-Smolt transformation of Atlantic salmon (Salmo salar L.)

Serum cortisol concentrations were measured in juvenile Atlantic salmon (Salmo salar L.) undergoing the parr-smolt transformation in fresh water, at either 1 year (S1 population) or 2 years (S2 population) after hatching. Serum cortisol levels were generally low (less than 10 ng ml-1), but during smoltification became significantly elevated in both populations. In addition, the S2 population showed a small cortisol peak in the autumn prior to smoltification. Simultaneous measurement of gill (Na + K) ATPase activity and serum cortisol concentrations in S2 salmon juveniles revealed that both features rose during smoltification in fresh water. The rise in gill (Na + K) ATPase activity was independent of cortisol levels, and preceded the rise in cortisol titer by approximately 1 month. After seawater transfer, gill enzyme levels remained high while cortisol titers fell sharply. Serum cortisol levels, but not gill (Na + K) ATPase activities, were progressively reduced by acclimation of smolts to increasing salinities. Linear regression studies indicated that, at any one level of gill (Na + K) ATPase, cortisol titer increased with increasing surface area: volume ratio. Extracellular fluid volume (sodium space) was found to decline with increasing gill (Na + K) ATPase activity, and to increase with serum cortisol titers. These results indicate that high serum cortisol levels represent a secondary response caused by the development of hypoosmoregulatory ability while still resident in fresh water. Cortisol does not appear to directly stimulate gill (Na + K) ATPase activity in Atlantic salmon smolts.

Ultrastructural and histochemical observations regarding the ovarian follicles of the amago salmon (Oncorhynchus rhodurus)

Pre- and postovulatory ovarian follicles of the amago salmon were investigated with special consideration given to the steroid production site. In the preovulatory specimens, the special thecal cells contained abundant mitochondria and smooth endoplasmic reticulum, as in the case of other steroid-producing cells, while the granulosa cells developed rough endoplasmic reticulum like protein-secreting cells. Remarkably ultrastructural changes occurred in the granulosa and the special thecal cells during the oocyte maturation stage; dilation of rough endoplasmic reticulum in the former cell and further development of smooth endoplasmic reticulum in the latter one. Histochemical reactions of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity were only positive in the special thecal cells of the postovulatory follicles. These results strongly suggest that the special thecal cells are the major sites of estrogen precursor synthesis in the amago salmon ovary.

Efferents from the supracommissural ventral telencephalon in the hime salmon (landlocked red salmon, Oncorhynchus nerka): an anterograde degeneration study

Efferents from the area ventralis telencephali pars supracommissuralis (Vs) of hime salmon (landlocked red salmon, Oncorhynchus nerka) were studied using anterograde degeneration methods. It was found that Vs sends intratelencephalic fibers bilaterally to the internal cell layer of the olfactory bulb and wide areas of telencephalon, while it sends extratelencephalic fibers bilaterally to habenulae, inferior lobes and midbrain tegmenti through medial and lateral forebrain bundles and lateral preoptic area. A possibility was pointed out that some of these extratelencephalic projections are involved in the pathway controlling the sexual behavior which are suggested from behavioral experiments.

The immunocytochemical localization of pituitary somatotrops in the genus Oncorhynchus using an antiserum to growth hormone of chum salmon (Oncorhynchus keta)

Pituitary somatotrops were localized in four species from the genus Oncorhynchus using an antiserum to chum salmon (Oncorhynchus keta) growth hormone. The antiserum cross-reacted specifically with the acidophils in the caudal pars distalis of all species tested. Corroborative immunodiffusion studies were also conducted with pituitary homogenates from the same species. Immunological identity of the GH molecule was observed for all species tested.

Immunocytochemical identification of thyrotropin (TSH)-producing cells in pituitary glands of several species of teleosts with antiserum to human TSH beta subunit

A rabbit antiserum raised against human thyrotropin (TSH) beta subunit (anti-human beta-TSH) was used to identify TSH cells in the pituitaries of five species of teleosts by means of the unlabeled antibody peroxidase-antiperoxidase (PAP) technique. The anti-human beta-TSH reacted only with polygonal basophils located in the rostral pars distalis (RPD) in the pituitaries of sexually immature eel (Anguilla japonica). In the pituitaries of medaka (Oryzias latipes) and white-edged rockfish (Sebastes taczanowskii), this serum reacted specifically with only one cell-type located in the antero-dorsal proximal pars distalis (PPD) and antero-ventral PPD, respectively. In the pituitaries of two species of salmonids, sexually immature rainbow trout (Salmo gairdneri) and sexually mature chum salmon (Oncorhynchus keta), the anti-human beta-TSH bound to the polygonal basophils in the ventral PPD adjacent to the RPD. Thus, the present immunocytochemical study identified polygonal basophils located in the RPD or PPD as TSH cells in five species of teleosts.

Granular epithelioid cells in the kidney of the Atlantic salmon (Salmo salar)

Two-year-old salmon at the migrating stage were kept in two different aquaria, the one containing seawater, the other freshwater. The fish kept in seawater showed retarded growth at the beginning of the year, but their growth had caught up with and passed the freshwater fish by the end of the year. At this time, 69 out of 79 of the freshwater fish died without any evident reason. When the fish were in seawater or freshwater at the biologically appropriate time, the number of granular epithelioid cells was equal in both groups. But the fish forced to remain in freshwater subsequently developed a considerably higher number of epithelioid cells. This may reflect an effort to maintain normal blood pressure.

Capillary distribution and metabolic histochemistry of the lateral propulsive musculature of pelagic teleost fish

Metabolic and vascular adaptation of teleost lateral propulsive musculature to an active mode of life was investigated in four pelagic teleosts (mackerel, yellowtail scad, pilchard and Australian salmon). Histochemical profiles and capillarisation data of the red and white muscle were compared to those of less active demersal species. Pelagic white muscle stained positively for the aerobic enzymes succinate dehydrogenase and NADH diaphorase, and had both subsarcolemmal and intermyofibrillar mitochondria which corresponded to the loci of the histochemical stain. Subsarcolemmal mitochondria tended to be localised close to capillaries. In contrast, white muscle from demersal species was unstained for the same enzymes and was devoid of mitochondria. Red muscle of all species had abundant mitochondria and stained intensely for aerobic enzymes. Capillarisation was quantified by determining the percentage of fibres surrounded by a given number of peripheral capillaries, mean fibre diameter, mean number of peripheral capillaries, capillary: fibre ratio and sharing factor where appropriate. Red muscle of mackerel, Australian salmon, pilchard and scad are better vascularised than red muscle of the flathead having 153, 200, 242, 291 and 309 microns 2 of cross-sectional fibre area per peripheral capillary, respectively. White muscle of mackerel, pilchard and scad are better vascularised than white muscle of the Australian salmon and flathead having 2040, 3367, 4992, 9893 and 10,469 microns 2 of cross-sectional fibre area per peripheral capillary, respectively. Red muscle of Australian salmon had distinct regional variation. Deep red muscle was found to be more highly vascularised (4.2 peripheral capillaries per muscle fibre) than lateral red muscle (1.9 peripheral capillaries per muscle fibre). Red muscle of the other species was less heterogeneous. White muscle capillarisation was slightly variable in all species. It is concluded that the white muscle of the pelagic species studied is functionally and structurally adapted for sustained aerobic activity with relatively abundant mitochondria being preferentially situated close to the source of gas and metabolite exchange.

Nucleus praeopticus and nucleus lateralis tuberis of Salmo salar and Salmo gairdneri: structure and relationship to the hypophysis

The nucleus praeopticus (NPO) is located on both sides of the preoptic recess and is composed of a pars parvocellularis and a pars magnocellularis. Only in the rainbow trout does the pars magnocellularis consist of separately located medium-sized cells and very large cells. Cytologically, three cell types can be distinguished: 1) unipolar cells ending in the cerebrospinal fluid (CSF), 2) bipolar cells also ending in the CSF and forming an axon, and 3) multipolar cells which generally do not have a direct connection with the ventricle. Axons originate from the cell bodies forming the paired preopticohypophysial tract that runs along the border of the diencephalon and the optic tract. A considerable number of NPO fibers leading to the hypophysis makes close contact with the cell bodies of the pars lateralis of the nucleus lateralis tuberis, indicating a functional relationship. Most NPO fibers terminate in the caudal part of the neurohypophysis, around blood capillaries and at the basal lamina of the pars intermedia. Far fewer fibers appear to terminate near the boundary of the neurohypophysis and the rostral and proximal pars distalis. The nucleus lateralis tuberis (NLT) is located in the caudal hypothalamus, beginning at the rostral end of the horizontal commissure and extending caudally beyond the hypophysial stalk. It consists of the partes rostralis, medialis, lateralis and ventrolateralis. In both species the p. rostralis contains small subependymal neurons and some larger ones. Only in the p. medialis of the Atlantic salmon are large cells present. In both species the most prominent part is the p. lateralis, which consists solely of large cells. Cells situated between the p. medialis and the p. lateralis are grouped in the p. ventrolateralis. It was impossible to trace the axons originating in the NLT, since the cyto- and axoplasm could not be stained specifically. The structure of the NPO and NLT in the two salmonid species is compared with that of other teleosts.

Considerations of a method of analyzing diallel crosses of atlantic salmon

Inferences derived from a proposed mixed model analysis of a diallel cross involving four stocks of Atlantic salmon (Salmo salar) are illustrated with growth data on weight and length. Variation between stocks was more apparent when samples represented dams as opposed to sires, thus stressing the relative importance of maternal effects. However, the ranking of stocks was not altered when either the means of sire sources or the means of dam sources were considered. No heterotic effects were found for the growth traits studied.

Gonadotropic cells in the Atlantic salmon, Salmo salar. An experimental immunocytological, electron miscroscopical study

The gonadotropin-producing cells (GTH-cells) in the Atlantic salmon were studied light and electron microscopically before, during and after spawning, and after injections of luteinizing hormone-releasing hormone (LH-RH). The double immunofluorescent technique was applied using rabbit anti-carp GTH as the first antibody. Numerous immunofluorescent cells were observed throughout the pars distalis, but very few in the pars intermedia. These cells are basophilic and PAS-positive, and ultrastructurally classified as globular gonadotropes. Only one gonadotropic cell type could be identified; its size, morphology and fine structure vary considerably. In the same specimen the GTH-cells can be predominantly globular or vesicular in appearance, depending on the reproductive phase of the fish. At spawning and after LH-RH injection, many GTH-cells reach a vacuolar stage; the content of the vacuoles is not immunofluorescent. Another cell type, which resembles GTH-cells in semi-thin sections, did not show gonadotropic properties; its nature and functional significance are unknown. In addition, the present study revealed an increase in the synthetic and exocytotic activity of prolactin cells after LH-RH injections. It is suggested that LH-RH mediates this effect via LH and eventually via estradiol.

Localization of monoamines in the forebrain of two salmonid species, with special reference to the hypothalamo-hypophysial system

In the salmon and trout aminergic cell bodies were found in the nucleus recessus lateralis (NRL) and the nucleus recessus posterioris (NRP), both of which are situated near the third ventricle. Three cell types could be distinguished. Type 1 produces a green and type 2 a yellow fluorescence. The former type probably contains dopamine and the later 5-hydroxytryptamine. Both types possess intraventricular protrusions in contact with the cerebrospinal fluid. The third cell type produces a less intense blue-green fluorescence; relatively few cells of this type have thick processes in contact with the ventricle. In addition, large fluorescent cells were found in the salmon, dorsal from the caudal part of the NRL. The various parts of the NRL and NRP are interconnected by thick bundles of nerve fibers; tracts leaving the nuclei could be traced for short distances only. The cells of the nucleus praeopticus (NPO), those of the medial part and to a much lesser extent also of the lateral part of the nucleus lateralis tuberis (NLT) have an aminergic innervation which probably originates form the NRL and/or NRP. All parts of the neurohypophysis contain many monoaminergic fibers, with aminergic material concentrated at the neuro-adenohypophysial interface. Fibers were not observed to penetrate the basal lamina. In the salmon and trout the fibers have a similar distribution, but differ in the intensity of fluorescence, being high in the salmon and low in the trout. Only in the trout have fluorescent cells been found in the adenohypophysis and very occasionally in the neurohypophysis. A number of these cells are basophilic and show a PAS-positive reaction.

Comparison of Mauthner cell size in teleosts

The Mauthner cells (M-cells) are a pair of neurons found in the medulla oblongata of most fish and amphibians. This neuron is not the same size in all teleosts. Based on the hypothesis that differences in M-cell size might be related to fish family and possibly fish habitat, M-cell and nuclear size were compared between fish families. In order to minimize effects of fish length on cell or nuclear size, statistical treatment of the data was made for four separate length classes. The results indicate at least three groupings by cell or nuclear size. The cell is large in fish from the Salmonidae, Catostomidae and Cyprinidae, small in the Stichaeidae, Cottidae and Pleuronectidae and absent in Batrachoididae, Lophiidae, Ogcocephalidae and Cylopteridae. In general a correlation exists between fish that lack or have small M-cells and a demersal habitat. Since these fish may rely on camouflage for protection against predation, the M-cells may have altered excitability or function as compared to more active fish in which the M-cell is known to function in initiating the startle response (larval zebrafish and goldfish). Differences in input to M-cells of different sizes in conjunction with known electrophysiological properties of the goldfish M-cell are discussed in relation to the function of this neuron.

The vascularization and the neuroendocrine pathways of the pituitary gland in the Atlantic salmon, Salmo salar

The pituitary gland of the Atlantic salmon, Salmo salar, is supplied by two arterial systems. The hypophysial arteries irrigate the rostral neurohypophysis and the pars distalis. The caudal hypothalamic arteries enter the neurointermediate lobe. In contrast with the capillary plexa in the neurohypophysis, the dorsal arteriol loops lack neurocrine terminals. An elaborate system of branches of the perivascular spaces extends into the neurohypophysis and it is continuous with the basement membrane in the neuroadenointerface and the intercellular channels of the pars distalis. This system is assumed to be an efficient conveyor of neurocrine factors and hypophysial hormones and an important vascular component. In the salmon the brain mediates its information to the pituitary through neurovascular links and the cells of the adenohypophysis are not innervated.The rostral neurohypophysis fulfills all criteria of being a median eminence although it lacks a well-defined portal system and it represents a secondary development from an original type seen in gnathostome vertebrates. It is suggested that the direct innervation of the endocrine cells in the pars distalis is a specialization and appeared late in the evolution of the teleost pituitary.

Influence of salinity on ultrastructure of the secretory cells of the adenohypophyseal pars distalis in yearling coho salmon (Oncorhynchus kisutch)

Six different types of secretory cells were identified by light and electron microscopy in the adenohypophyseal pars distalis of yearling coho salmon acclimated to fresh or salt water. Prolactin cells are markedly more active in the freshwater than the seawater fish; these cells exhibit definite functional activity 3 days after transfer from salt to fresh water, indicating an osmoregulatory role of prolactin in the freshwater environment. Plasma sodium showed a significant decline 6 h after transfer from sea water to fresh water and, even after 1 week, remained lower than in the fully acclimated freshwater fish. Corticotropic (ACTH) cells did not appear cytologically different in freshwater and seawater fish. GH cells, the most prominent cells in the proximal pars distalis, appear more numerous and more granulated in the seawater fish, suggesting an osmoregulatory involvement in young coho salmon. Putative thyrotropic (TSH) and putative gonadotropic cells (GTH) can be distinguished by differences in granulation; only one type of GTH cell is evident with ultrastructural features that differ from those of sexually mature salmon. Stellate, non-granulated cells occur in all regions of the adenohypophysis but more frequently in the prolactin follicles; they are much more prominent in the seawater than freshwater fish.

[Preoptic-hypophyseal neurosecretory system of the Baikal salmon, Coregonus autumnalis migratorius, during the prespawning period]

It has been shown that functional condition of the preoptic-hypophyseal neurosecretory system (PHNS) in the fish studied is associated with the activity of population. During early spring, when the fish are not yet completely active after winter, the PHNS is characterized by a low level of activity (accumulation of the neurosecretory substance and neurohypophysis, as well as moderate extrusion of the neurosecretory material along the axons beyond the preoptic nucleus). In July, some activation of synthesis and extrusion of the neurosecretory substance from cells of the preoptic nucleus and significant accumulation of the substance in the neurohypophysis are observed. In August and especially in September, during spawning migration, the rate of extrusion of the neurosecret from the preoptic nucleus and the extrusion of the neurohormones from neurohypophysis into the blood flow significantly increase. Neurosecretory cells of the preoptic nucleus remain highly active. During the same period, infiltration of the preoptic nucleus by leucocytes and neuronal hydroencephalokrynia are observed. During spawning migration, females (in contrast to males) exhibit more, significant decrease in the bulk of neurosecretory substance in the neurohypophysis, which is presumably associated with higher energy expenditures for the completion of ovogenesis.

Structure of the nongranulated cells in the hypophyseal rostral pars distalis of cyclostomes and actinopterygians

The structure of the nongranulated cells in the sea lamprey adenohypophysis and similar cells of the rostral pars distalis in a number of actinopterygian fishes was examined with the aim of determining the role(s) of these cells in pituitary function. A number of possible roles are proposed for the nongranulated cells. In salmonids and Amia calva the cells may be involved in the active movement of material into or from the follicle lumina. The structure of the nongranulated cells in in vitro cultured and in in vivo transplanted trout rostral pars distalis also suggests a phagocytotic role for these cell. In teleosts with a non-follicular rostral pars distalis the nongranulated cells and in the subsequent dispersal of the hormone (and/or carrier substance) into the peripheral circulation.

The fine structure of the epidermis of two species of salmonid fish, the Atlantic salmon (Salmo salar L.). and the brown trout (Salmo trutta L.)

The fine structure of epidermal mucous cells of two species of salmonid fish has been described. Mucous cells are, next to filament-containing cells, the most commonly encountered cells in fish epidermis. The development of the cells as they progress to the periphery has been characterised. They are initially difficult to distinguish from filament-containing cells: later, they can be recognised by the presence of much smooth-surfaced E.R. The mucigenesis and the subsequent secretion of mucus has been observed and it is essentially comparable to that which occurs in the mucous cells of the mammalian intestine. The mucous layer of the epidermal surface seems to mainly comprise of the products of these mucous cells and the "cuticle" seen in other species has not yet been observed in the salmonid species investigated here.