Mortality of pre-smolt Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., caused by fluctuating water levels in the regulated River Nidelva, central Norway

The river Nidelva, situated in central Norway, is regulated for production of electricity. Water discharge may vary from 150 to 30 m3 s -1 over a period of 10 min at the outlet of the power stations. The water level then sinks 50 cm during the next 30 min. The Nidelva produces both salmon and trout. Water fluctuations were found responsible for large losses of O+ salmon and trout. The recruitment of salmon was concluded as satisfactory, while recruitment of trout was reduced as a result of stranding.     

Summer and fall microhabitat utilization of juvenile bull trout and cutthroat trout in a wilderness stream, Idaho

Microhabitat use and availability were evaluated and compared between different size classes of juvenile resident bull trout (Salvelinus confluentus) and cutthroat trout (Oncorhynchus clarki) in a small wilderness stream within the South Fork Clearwater River basin, Idaho. The objective was to determine if utilization of measured habitat characteristics changed from summer to late fall. Sampling of fish was conducted with night snorkeling. During the summer, smaller juvenile bull trout (<66 mm) total length (TL) were associated with shallow stream margins over coarse substrates. In the fall, they moved to significantly deeper, lower velocity water, and closer to cover (p<0.05), but maintained their association with coarse substrates. During the summer, larger juvenile bull trout and larger juvenile cutthroat trout (66–130 mm TL) occupied significantly deeper water than smaller juvenile bull trout (p<0.05). Generally, larger juvenile bull trout were found closer to the bottom and in lower velocity water than larger juvenile cutthroat trout (p<0.05). In the fall, larger juvenile bull trout and larger juvenile cutthroat trout were associated with significantly deeper, lower velocity water located closer to cover than in summer (p<0.05). However, cutthroat trout occupied slightly deeper water over finer substrates than bull trout. Deep water with low velocities evidently provide important rearing areas for large bull trout and large cutthroat trout in the fall. Land management practices that maintain such environments will benefit these species.     

Post-hatching development of the thymic epithelial cells in the rainbow trout Salmo gairdneri: an ultrastructural study

This study reports the ultrastructure of subpopulations of epithelial cells of the thymic parenchyma during the post-hatching development of the rainbow trout, Salmo gairdner, kept at 14 degrees C. At hatching, the thymus contained a small number of medium and large thymocytes interspersed among three different types of epithelial cells: (1) epithelial cells adjacent to the connective tissue capsule; (2) ramified dark epithelial cells with electron-dense cytoplasm; and (3) pale electron-lucent epithelial cells displaying secretory-like features. All these cells types were anchored to one another by desmosomes and had apparently differentiated from the pharyngeal epithelium. At 4 days after hatching, the thymus enlarged, and numerous gaps occurred between the cell processes of contiguous epithelial cells adjacent to the capsular connective tissue. In 21-day-old trout, thymic trabeculae developed carrying blood vessels, and a subcapsular zone became evident containing lymphoblasts and large subcapsular epithelial cells. In 30-day-old trout, an outer thymic zone developed consisting of spindle-shaped epithelial cells which formed a dense network. At this stage, scattered cystic cells, which apparently differentiated from the pale epithelial cells, were present.     

A comparison of the effect of long-term starvation on responses to low-temperature stress by juvenile rainbow (Oncorhynchus mykiss) and brown (Salmo trutta) trout reveal different responses in the two species

Biometric parameters and oxidative stress indicators were measured in liver and muscle samples from rainbow trout and brown trout juveniles exposed to a 45-day starvation period at low water temperature. As a general tendency, hepatic antioxidant enzyme activities in both species increased with fasting to eliminate the harmful effects of reactive oxygen species (ROS). However, the metabolic response to food deprivation in the muscle of each species was different. Lipid peroxidation levels in both species increased with starvation. We concluded that (1) low water temperature enhances ROS production in salmonids because of increased polyunsaturated fatty acid content in the cell membrane; (2) starvation significantly impaired the growth parameters of brown trout, yet the reverse was found for rainbow trout; and (3) despite this negative interaction, brown trout juveniles can physiologically tolerate oxidative stress caused by starvation and can therefore be cultivated under stressful conditions even in their early life stages.     

Sub-lethal plasma ammonia accumulation and the exercise performance of salmonids

The proposal that plasma ammonia accumulation might impair the swimming performance of fish was first made over a decade ago, and has now proven to be the case for a number of salmonid species. The first experimental evidence was indirect, when a negative linear relationship between plasma ammonia concentrations and maximum sustainable swimming speed (U(crit)) was found following the exposure of brown trout (Salmo trutta) to sub-lethal concentrations of copper in soft acidic water. Since then, negative linear relationships between plasma ammonia concentration and U(crit) have been demonstrated following exposure of brown trout, rainbow trout (Oncorhynchus mykiss) and coho salmon (Oncorhynchus kisutch) to elevated water ammonia. For brown trout, the relationships between plasma ammonia and U(crit) were remarkably similar following either exposure to elevated water ammonia or to sub-lethal copper. This indicates that the impairment of swimming performance resulting from exposure to sub-lethal concentrations of heavy metals may be attributable in large part to an accumulation of endogenous ammonia. The negative relationship between plasma ammonia concentration and U(crit) was similar in size-matched rainbow and brown trout but, under similar regimes of ammonia exposure, rainbow trout were able to maintain a significantly lower plasma ammonia concentration, revealing inter-specific differences in ammonia permeability and/or transport. One primary mechanism by which ammonia accumulation may impair exercise performance is a partial depolarisation of membrane potential in tissues such as the brain and white muscle. This may prejudice the co-ordination of swimming movements and reduce or abolish the development of muscle tension, thus, compromising swimming efficiency and performance at the top end of the range.     

STUDIES ON ENZYME ACTION : XLVI. THE ESTER-HYDROLYZING ACTIONS OF WHOLE TROUT PREPARATIONS UNDER VARIOUS CONDITIONS.

The ester-hydrolyzing actions of trout extracts at different hydrogen ion concentrations were studied. It was pointed out that the behavior was similar to that found with various tissue and tumor materials and that similar relations hold. Glycerol solutions extracted somewhat larger amounts of active enzyme material from trout than did water and sodium chloride solutions, although the differences were not large. Evidence was presented for the existence of a so called "coenzyme."     

Spermiogenesis in the rainbow trout (Salmo gairdneri)

In an ultrastructural study on the spermiogenesis of the rainbow trout (Salmo gairdneri R.) four spermatogenetic stages were identified. In young round spermatids, the nuclear chromatin was first heterogeneous (euchromatin and heterochromatin). Subsequently, it became more homogeneous and started to condense in the form of coarse granules and fibers and then into fibrils associated in ribbon-like elements which eventually partly fused together. During early spermiogenesis, a juxtanuclear vacuole appeared in the area where the nuclear envelope was specialized due to condensation of material between the two envelopes and a slight accumulation of nuclear material. This area was finally located in the anterior part of spermatids and spermatozoa; it probably plays a role during fertilization. A flagellar rootlet appeared early in spermiogenesis; it may play a role in the attachment of the flagellum to the nucleus since it persisted until the centriolar complex was definitively fixed in the implantation fossa. The flagellum did not display a plasma membrane and was first located in the cytoplasm, but when it was later extruded from the cell, it acquired a membrane. The cytoplasm was rich in ribosomes (free or in small groups) but poor in membranous organelles. The few mitochondria polarized around the centriolar complex were finally organized into an annular mid-piece. The spermatids remained connected by intercellular bridges until the end of spermiogenesis. The complexity of trout spermiogenesis is intermediate between that in poecilids and that in carp and pike, which have very simple spermatozoa. The role of the material from the nucleus and the cytoplasm reaching the Sertoli cell in the control of spermatogenesis has been discussed.     

Mycological aspects of a disease of young perch in Windermere

A disease of young perch in Windermere was investigated. In contrast to the case of U.D.N. infections of salmon and trout, a variety of fungi were obtained from the diseased fish. These reflected the spora present in the water at the same time to a large extent. An exception was Saprolegnia ferax , which did not grow on the fish and indicated that some degree of host specificity was involved. The Achyla isolates, both from the fish and from the water, were found to be heterothallic and male in reaction.     

鹅掌楸油细胞的发育解剖学研究

鹅掌楸油细胞比相邻组织细胞分化,因而在叶肉细胞未完全分化的叶原基、幼叶以及未完全分化的幼茎中,都可看到已分化的油细胞。通常,在第二叶原基中可发现油细胞原始细胞,由于其染色深、细胞核大而易与周围组织的细胞相区别。以后,油细胞逐步液泡化,直至形成一个大的液泡,此时,细胞核呈扁平状,并与细胞质一起成为一薄层围绕着大液泡。当油细胞发育成熟后,细胞质及核开始解体,整个油细胞的腔由大液泡充满,成为油囊,在部分     

Assessment of thyroid function in adult medaka (Oryzias latipes) and juvenile rainbow trout (Oncorhynchus mykiss) using immunostaining methods

The effect of injected bovine TSH on the pattern of anti-T(4) and anti-T(3) immunostaining of the thyroid tissue was examined in rainbow trout (Oncorhynchus mykiss) and medaka (Oryzias latipes) to determine if the previously reported immunostaining of the cytoplasm of thyrocytes is due to the presence of colloid pinocytotic vesicles and is thus indicative of thyroid hormone release. We hypothesized that the number of immunostained thyrocytes should increase following a TSH challenge, and this should parallel other indicators of increased thyroid activity. In medaka, immunostained thyrocytes were only found following the TSH challenge, and were most marked after 24 to 72 hours; the immunostaining was associated with large colloid-filled cytoplasmic vesicles. In trout, the number and staining intensity of immunostained thyrocytes were increased after the TSH challenge; the immunostaining was present throughout the cytoplasm of the thyrocytes. These findings support the working hypothesis that the immunostaining of the thyrocytes is associated with the pinocytosis of thyroglobulin by the thyrocytes in parallel with an increase in release of thyroid hormone, and that this investigational approach provides a reliable indicator of thyroid hormone release activity.     

Influence of temperature and membrane lipid composition on the osmotic water permeability of teleost gills.

Osmotic water uptake was measured gravimetrically in isolated, ligated gill arches from trout (acclimated to and incubated at 5 degrees and 20 degrees C) and tilapia (21.5 degrees and 33 degrees C). For both species, incubation of arches at the higher temperature led to 1.5- to 3-fold greater measures of water weight gain. However, gills from warmer-acclimated trout and tilapia had 1- to >3-fold lower the initial rate and 1.5- to >2.5-fold lower the extent of water uptake seen in colder-acclimated conspecifics. Both the incubation temperature sensitivity and the acclimation effects are consistent with transmembrane water permeation. Calcium-free incubations (permitting paracellular water movement) also indicated that interfacial cell membranes contribute to gill permeability characteristics; without calcium, trout gill osmotic water uptake values increased 1.5- to 2-fold, and the temperature dependence of water uptake decreased (initial rate) or was eliminated (extent). The specific contribution of cholesterol to restricting barrier membrane water permeability was indicated by concentration-dependent increases in water uptake in the presence of either nystatin (a cholesterol-complexing, pore-forming agent) or methyl-beta-cyclodextrin (which selectively depletes membrane cholesterol). In addition, a cholesterol-specific cytochemical probe (filipin) intensely labeled the apical surface membranes of trout and tilapia gill epithelium. In summary, these studies implicate membrane cholesterol in determining water permeability in fish gills.     

The ultrastructure of the salt gland of Spartina foliosa

Summary The salt gland in Spartina foliosa is composed of two cells, a large basal cell and a smaller, dome-shaped cap cell which is located on a neck-like protrusion of the basal cell. There is no cuticular layer separating the salt gland from the mesophyll tissue. The basal cell has dense cytoplasm which contains numerous mitochondria, rod-like wall protuberances, and infoldings of the plasmalemma which extend into the basal cell and partition the basal cell cytoplasm. The protuberances originate on the wall between the basal and the cap cells and are isolated from the basal-cell cytoplasm by the infoldings of the plasmalemma. While the cap cell has no partitioning membrane system or wall protuberances, it resembles the basal cell by having dense cytoplasm and numerous mitochondria.The basal cell seems to be designed for efficient movement of ions toward the cap cell. The long, dead-end extracellular channels in the basal cell of Spartina appear comparable to surface specializations seen in the secreting epithelium of animal cells which carry out solute-linked water transport. The number of mitochondria and their close association with the plasmalemma extensions suggest that they have an important role in the transfer of ions through the basal cell.The accumulated ions would move into the extracellular spaces along an osomotic gradient where the accompanying passive flow of water would move the ions into the cap-cell wall and from there the solution would pass out through the pores in the cuticle.     

Structure and genetic diversity of small populations of brown trout Salmo trutta in Kandalaksha Bay,the White Sea

The phenetic variability (types of life strategy, age and sex structure of population, biological peculiarities), the anthropogenic pressure, and the genetic diversity were studied by five microsatellite loci for several minor populations of brown trout Salmo trutta inhabiting the waterbodies of Velikaya Salma Strait watershed area (Kandalaksha Bay, the White Sea). The level of genetic and phenetic diversity in small populations was comparable to those representing large water systems. Significant spatial dissimilarity of the populations located in less than 15-km distance was found. Low allelic and genetic diversity was observed for the studied populations. Variability of some studied loci through the time period was observed for the fish sampled from different populations. We assume that minor populations of brown trout may be treated as the standards of native populations for the monitoring activities on the brown trout populations and its environment both in short-term and long-term perspective.     

Fine structure of sacciform cells in the epidermis of the brown trout, Salmo trutta

The fine structure of a cell type in the epidermis of brown trout, Salmo trutta L., is described. Its cytological features are compared with those of other sacciform cells reported in several species of teleost fish. This cell type also has a highly electron-dense cytoplasm with numerous Golgi systems and extensive rough endoplasmic reticulum. However, surrounding the large central vacuole there are no peripheral vesicles—'bubbles'—which are characteristic features in non-salmonid teleosts. Instead of these, in the vacuole there are cytoplasmic intrusions of circular cross-sections forming a mesh in the cortical zone. Inside these intrusions there are granules which are interpreted as ribosomes trapped by fusion of the vacuole and reticulum membranes. The way in which the secretion is released into the lumen of the central vacuole is discussed. It is suggested that this proteinaceous material does not pass through the Golgi system, but flows directly from endoplasmic cisternae to the vacuole.     

The effects of aluminum and acid on the gill morphology in rainbow trout,Salmo gairdneii

Synopsis The objective was to determine the effects of acid and aluminum in acidified hard and soft water on the histology and morphometry of rainbow trout gills, and to determine relevant toxicity indicators within the gill tissue. Acid and aluminum promoted measurable primary epithelial hyperplasia which proved to be a reliable biological indicator of acid and aluminum contamination and possibly of some predictive value. Low levels of aluminum and acid resulted in hypertrophied chloride cells, suggesting a role in adapting to the contaminants. High concentrations of aluminum (>10 molI^-1) caused chloride cell necrosis and consequently a decline in cell numbers over time. Aluminum precipitates accumulating within the chloride cell cytoplasm probably lead to impaired function prior to cell degeneration. The morphological alterations resulted in a decrease in water space between secondary lamellae (up to 40% within 14 d) which may reduce the efficiency of gas exchange. Twice the aluminum was required in hard water to elicit a similar soft water tissue response. Pathological changes were more severe with aluminum at pH 5.2 than at pH 4.7; results of aluminum speciation suggest that both labile and non-labile fractions are responsible for the induction of gill lesions. Low levels of aluminum may protect fish from the effects of high hydrogen ion concentration.     

Ultrastructural evidence for apoptosis of pavement cells, chloride cells, and hatching gland cells in the developing branchial area of the trout Salmo trutta

Death by apoptosis of branchial epithelial cells was studied in brown trout embryos by means of transmission electron microscopy. Superficial pavement cells are sloughed off for the renewal of the epithelium after an apoptotic degeneration with shrinkage of the cytoplasm and loss of desmosomal contacts. Chloride cells appear as immature, mature and degenerating cells. Degenerating chloride cells, which are separated from the ambient water by pavement cells, show condensation of the cytoplasm and structural alterations in the tubular system and the mitochondria. Hatching gland cells degenerate either into apoptotic bodies or into cellular debris, depending on the functional stage of the cell. There was no phagocytosis by macrophages or adjacent cells of the degenerating chloride and hatching gland cells, but an infiltration of leucocytes was always observed in the epithelium undergoing cellular degeneration. In some instances, secondary necrosis of apoptotic hatching gland cells was observed. Apoptosis occurs in the three types of cells since early stages of development. However, a massive wave of cellular death occurred in pavement and hatching gland cells during the hatching stage and in the chloride cells during post-hatching stages.     

Timing of predation by rainbow trout controls Daphnia demography and the trophic status of a Minnesota lake

1. Stocking of lakes with rainbow trout is a common practice that presents a potential conflict for lake managers who must balance the interests of anglers with those concerned that zooplanktivory by trout may trigger a trophic cascade and result in decreased water clarity. 2. This study examined how the timing of trout stocking (autumn versus spring) in a Minnesota (U.S.A.) lake affected (i) the population dynamics of their zooplankton food supply (Daphnia pulicaria), (ii) phytoplankton biomass and water clarity and (iii) trout survival. Sizes of both Daphnia and trout populations were estimated acoustically with high‐frequency (192 kHz) sonar. 3. Daphnia were nearly eliminated from the lake during winters after trout were stocked in autumn. In both of these years (1996 and 1997), the Daphnia population was small in the spring, and grew during the summer and into the autumn as the trout population diminished. 4. The lake was then stocked in spring for 2 years (1998 and 1999). This fisheries manipulation alleviated predation over the winter, but increased predation on D. pulicaria during the spring, summer and autumn. However, the high mortality caused by the spring‐stocked trout was offset by even higher rates of reproduction by the relatively large populations of fecund Daphnia that survived the winter in 1998 and 1999. 5. Grazing by these dense populations of Daphnia produced clear‐water phases during May and June that were inhibited in autumn stocking years. In addition, the large Daphnia populations present during the spring and early summer of 1998 and 1999 provided abundant forage for trout. 6. This fisheries manipulation achieved seemingly mutually exclusive management objectives: a robust planktivorous sport fishery, and clear water for other forms of recreation.     

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

Summary In the salmon and trout aminergic cell bodies were found in the nucleus recessus lateraralis (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 latter 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 from 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.     

Cadmium-induced changes in gill morphology of zebrafish, Brachydanio rerio (Hamilton–Buchanan), and rainbow trout, Salmo gairdneri Richardson

Freshwater zebrafish and brackish water rainbow trout were exposed to different concentrations of cadmium for up to 6 weeks. The gill morphology was examined by light and electron microscopy, and a morphometric analysis was performed. The morphometric study of the secondary lamellae revealed an increase in the portion exterior to the basal lamina, resulting in an increased diffusion distance, after exposure to cadmium concentrations of 10μg l⁻¹ and above. In both species this was due to an increase in volume of the non-tissue spaces of the secondary lamellar epithelium. Furthermore, the water space between neighbouring secondary lamellae was clearly reduced. Morphological examination revealed some gross alterations compared with control fish. These initially consisted in curling of the secondary lamellae and finally resulted in local teleangiectasia. Partial lifting of the secondary lamellar epithelium from the pillar cells resulted in large non-tissue spaces which were invaded by leucocytes. The first sign of degeneration was observed in the chloride cells, which were characterized by a dispersed cytoplasm and a smooth apical plasma membrane.     

The temperature–productivity squeeze: constraints on brook trout growth along an Appalachian river continuum

We tested the hypothesis that brook trout growth rates are controlled by a complex interaction of food availability, water temperature, and competitor density. We quantified trout diet, growth, and consumption in small headwater tributaries characterized as cold with low food and high trout density, larger tributaries characterized as cold with moderate food and moderate trout density, and large main stems characterized as warm with high food and low trout density. Brook trout consumption was highest in the main stem where diets shifted from insects in headwaters to fishes and crayfish in larger streams. Despite high water temperatures, trout growth rates also were consistently highest in the main stem, likely due to competitively dominant trout monopolizing thermal refugia. Temporal changes in trout density had a direct negative effect on brook trout growth rates. Our results suggest that competition for food constrains brook trout growth in small streams, but access to thermal refugia in productive main stem habitats enables dominant trout to supplement growth at a watershed scale. Brook trout conservation in this region should seek to relieve the “temperature–productivity squeeze,” whereby brook trout productivity is constrained by access to habitats that provide both suitable water temperature and sufficient prey.