Sperm traits in farmed and wild Atlantic salmon Salmo salar

Differences in sperm metabolism and morphology between wild and non‐local farmed Atlantic salmon Salmo salar were assessed by measuring metabolic enzyme activities and length of sperm flagella. No differences were observed between wild and farmed S. salar sperm with regards to cell counts or any of the biochemical variables assessed. Flagella of sperm cells were significantly longer in wild than farmed S. salar; however, this did not result in higher energy levels or different fertilization rates.     

Water chemistry and its effects on the physiology and survival of Atlantic salmon Salmo salar smolts

The physiological effects of episodic pH fluctuations on Atlantic salmon Salmo salar smolts in eastern Maine, U.S.A., were investigated. During this study, S. salar smolts were exposed to ambient stream-water chemistry conditions at nine sites in four catchments for 3 and 6 day intervals during the spring S. salar smolt migration period. Plasma chloride, plasma glucose, gill aluminium and gill Na(+)- and K(+)-ATPase levels in S. salar smolts were assessed in relation to ambient stream-water chemistry during this migration period. Changes in both plasma chloride and plasma glucose levels of S. salar smolts were strongly correlated with stream pH, and S. salar smolt mortality occurred in one study site with ambient stream pH between 5·6 and 5·8 during the study period. The findings from this study suggest that physiological effects on S. salar smolts are strongly correlated with stream pH and that in rivers and streams with low dissolved organic carbon (DOC) concentrations the threshold for physiological effects and mortality probably occurs at a higher pH and shorter exposure period than in rivers with higher DOC. Additionally, whenever an acidification event in which pH drops below 5·9 coincides with S. salar smolt migration in eastern Maine rivers, there is potential for a significant reduction in plasma ions of S. salar smolts.     

Multiple central-place territories in wild young-of-the-year Atlantic salmon Salmo salar

1. The space use of central-place foragers, animals that forage from and return to a single central place such as a nest, burrow or sleeping site, is well documented. Limited data, however, exist for multiple central-place foragers that alternate among several central places. 2. The conventional view of stream-dwelling salmonids suggests that they conform to the central-place territorial model (CPTM) by (i) attacking prey and intruders from one primary foraging station, and defending (ii) small (iii) exclusive areas that (iv) increase with body size. 3. Recent studies suggest greater variability in salmonid space-use than would be expected by the CPTM, but tend to focus on the time allocated towards different activities rather than their distribution in space, especially for young-of-the-year (YOY) fish that are hard to tag and monitor in the wild. 4. In this study, the validity of CPTM was tested by mapping the daily space use of 50 YOY Atlantic salmon in a natural stream via repeated observations of tagged fish in diverse habitats, and by comparing these to earlier estimates of territory use in YOY salmonids. 5. The 50 YOY Atlantic salmon were multiple central-place foragers. All fish visited more than one foraging station (median = 12.5 stations), visited most stations (68.5%) repeatedly, showed limited fidelity to a particular station and typically attacked prey only while holding a position at a station. 6. The multiple central-place territories of the 50 fish were large (mean = 0.932 m(2)) compared to earlier territory size estimates (mean = 0.107 m(2)) for salmonids of similar size and, surprisingly, did not increase with body size. Focal fish attacked intruders from similar distances as reported earlier for much smaller territories, suggesting that large territories are less exclusively defended at any given time. 7. Overall, this study provides a new view on foraging and territoriality in stream salmonids, and on the small but diverse literature on multiple central-place foragers. Further studies, however, are needed to clarify the evolutionary benefits and population consequences of multiple central-place space-use in mobile animals.     

Evidence for episodic acidification effects on migrating Atlantic salmon Salmo salar smolts

Field studies were conducted to determine levels of gill aluminium as an index of acidification effects on migrating Atlantic salmon Salmo salar smolts in the north‐eastern U.S.A. along mainstem river migration corridors in several major river basins. Smolts emigrating from the Connecticut River, where most (but not all) tributaries were well buffered, had low or undetectable levels of gill aluminium and high gill Na⁺/K⁺‐ATPase (NKA) activity. In contrast, smolts emigrating from the upper Merrimack River basin where most tributaries are characterized by low pH and high inorganic aluminium had consistently elevated gill aluminium and lower gill NKA activity, which may explain the low adult return rates of S. salar stocked into the upper Merrimack catchment. In the Sheepscot, Narraguagus and Penobscot Rivers in Maine, river and year‐specific effects on gill aluminium were detected that appeared to be driven by underlying geology and high spring discharge. The results indicate that episodic acidification is affecting S. salar smolts in poorly buffered streams in New England and may help explain variation in S. salar survival and abundance among rivers and among years, with implications for the conservation and recovery of S. salar in the north‐eastern U.S.A. These results suggest that the physiological condition of outmigrating smolts may serve as a large‐scale sentinel of landscape‐level recovery of atmospheric pollution in this and other parts of the North Atlantic region.     

Migratory behaviour of wild and farmed Atlantic salmon (Salmo salar) during spawning

Migratory behaviour at spawning of wild and newly-escaped farmed Atlantic salmon was analysed by radio telemetry in the River Alta, North Norway. Spawning areas were located by aerial surveys. Farmed females moved significantly more than wild females ( P <0.01). There was no such difference between the two groups of males. About 83% of the wild fish stayed within identified spawning areas for 1 day or longer. The corresponding figure for farmed salmon was only 43% ( P <0.05). Wild salmon stayed 8.1 days inside spawning areas and farmed salmon 5.2 days. The present results suggest that escaped farmed salmon had reduced spawning success compared with wild fish.     

Characterization of an Atlantic salmon Salmo salar stream at the southern limit of its eastern Atlantic distribution

Ten reaches of an Atlantic stream located in north‐west Spain were sampled intensively during one summer to characterize the conditions where Atlantic salmon Salmo salar have been re‐introduced along the stream. Fish species richness and diversity showed a downstream increase, which was mainly attributed to the higher number of cyprinid species found in the lower reaches. Moreover, except for brown trout Salmo trutta that appeared to be the most ubiquitous species, the densities of the other species was higher in the lower than in the upper stream reaches. Redundancy analysis showed that the pattern of fish assemblages observed along the studied stream was mainly related to the expected gradient observed in the levels of dissolved oxygen, discharge and mean current speed. There was a significant differentiation between midstream and downstream reaches, both in terms of the composition of their fish assemblages and the freshwater habitat. This study emphasizes the importance of describing the variations in fish assemblages and habitat characteristics along a river to explore its relation to potential changes in the survival of fish populations. In particular, the development of habitat–fish relationships may be a useful tool for water managers to assess the effects of development and restoration projects on the habitat of S. salar.     

Gonadotropic cells in the Atlantic salmon,Salmo salar

Summary 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 semithin 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.The authors are indebted to Dr. N. Johansson and superintendent N. Steffner for generously providing facilities at their institutes in Älvkarleby. They also wish to thank Mrs. Y. Lilliemarck and Mrs. V. Lundin for their skillful technical assistance. The grants made available by the Swedish Natural Science Research Council (No. 2124-037) are also gratefully acknowledged. Thanks are also due to Mrs. S.M. McNab for linguistic assistance     

The effects of intraperitoneally implanted dummy acoustic transmitters on the behaviour and physiology of juvenile Atlantic salmon, Salmo salar L

The behavioural and physiological effects of surgical implantation of dummy miniature acoustic transmitters into the peritonealcavities ofjuvenile Atlantic salmon, Salmo salar L., were assessed. lntraperitoneal implantations had no significant effect on growth, feeding or swimming behaviour in either parr or smolts. Recovery from the surgical implantation was both rapid and total; infection was absent; and physiological processes such as smoltification and maturation of testes in precocious parr were unaffected. Expulsion of the transmitter through the body wall, not through the implantation wound, occurred in a number of fish but without adversely affecting the animals. The intraperitoneal implantation technique is discussed in relation to its use during biotelemetry studies.     

Chronic effects of low pH on length and weight of Atlantic salmon,Salmo salar

Synopsis Measurements were made on Atlantic salmon from five sources in New England. Fish were reared at pH 7.0 and 5.2 from hatch to 199, 270 or 440 days. Length and weight were smaller in Atlantic salmon, Salmo salar, that were continuously exposed to low pH in the laboratory. Length and weight in neutral pH water varied among fish from the different sources. Fish from the Green Lake, Craig Brook, and Tunison sources were not significantly different in their lengths over time. Cortland and landlocked Atlantic salmon were not significantly different from one another but were significantly different from the other three sources. At pH 5.2, there were no significant differences in length between fish from any of the five sources. The Cortland salmon were significantly different from the other four sources in respect to their weight over time at neutral pH. At pH 5.2, there were no significant differences between any of the five sources.Cooperators are the U.S. Fish and Wildlife Service, the Maine Department of Inland Fisheries and Wildlife, the University of Maine, and the Wildlife Management Institute     

Somatolactin mRNA expression during the parr–smolt transformation in hatchery-reared Atlantic salmon Salmo salar smolts

Expression of somatolactin (SL) mRNA was quantified during smoltification at 2 week intervals during January and February and weekly during March, April and May 2004 in a line-bred ranching stock of Atlantic salmon Salmo salar . Gene expression of SL (and a splice variant termed SL₁₈₀) was lower in fish sampled in the later weeks of smoltification than in those at the beginning, a pattern opposite to that of gill Na⁺ K⁺-ATPase activity.     

Identification of olfactory receptor genes in Atlantic salmon Salmo salar

It has been hypothesized that salmonids use olfactory cues to return to their natal rivers and streams. The key components of the molecular pathways involved in imprinting and homing, however, are still unknown. Aquatic chemical cues are received through the nares and into the nasal cavity that contains a single olfactory organ, the olfactory rosette. The olfactory rosette contains sensory neurons, each of which is thought to express only one olfactory receptor. If odorants are involved in salmonid homing migration then olfactory receptors should play a critical role in the dissipation of information from the environment to the fish. Therefore, to understand the molecular basis for imprinting and homing in Atlantic salmon Salmo salar it is important to identify and characterize the repertoire of olfactory receptors in this species. The first public assembly of the S. salar genome was searched for genes encoding three of the superfamilies of fish olfactory receptors: V2R-like (olfc), V1R-like (ora) and main olfactory receptor (mor). A further six ora genes were added to ora1 and ora2, which had been described previously. In addition, 48 putative mors were identified, 24 of which appear to be functional based on their gene structures and predicted amino-acid sequences. Phylogenetic analyses were then used to compare these S. salar olfactory receptor genes with those of zebrafish Danio rerio, two pufferfish species Takifugu rubripes and Tetraodon nigroviridis, medaka Oryzias latipes and three-spined stickleback Gasterosteus aculeatus.     

The effects of sustained aerobic swimming on osmoregulatory pathways in Atlantic salmon Salmo salar smolts

Atlantic salmon Salmo salar smolts were exposed to one of the four different aerobic exercise regimens for 10 weeks followed by a 1 week final smoltification period in fresh water and a subsequent eight‐day seawater transfer period. Samples of gill and intestinal tissue were taken at each time point and gene expression was used to assess the effects of exercise training on both branchial and intestinal osmoregulatory pathways. Real‐time polymerase chain reaction (PCR) analysis revealed that exercise training up‐regulated the expression of seawater relevant genes in the gills of S. salar smolts, including Na⁺, K⁺ ATPase (nka) subunit α1b, the Na⁺, K⁺, 2 Cl^? co‐transporter (nkcc1) and cftr channel. These findings suggest that aerobic exercise stimulates expression of seawater ion transport pathways that may act to shift the seawater transfer window for S. salar smolts. Aerobic exercise also appeared to stimulate freshwater ion uptake mechanisms probably associated with an osmorespiratory compromise related to increased exercise. No differences were observed in plasma Na⁺ and Cl^? concentrations as a consequence of exercise treatment, but plasma Na⁺ was lower during the final smoltification period in all treatments. No effects of exercise were observed for intestinal nkcc2, nor the Mg²⁺ transporters slc41a2 and transient receptor protein M7 (trpm7); however, expression of both Mg²⁺ transporters was affected by salinity transfer suggesting a dynamic role in Mg²⁺ homeostasis in fishes.     

Consistent melanophore spot patterns allow long‐term individual recognition of Atlantic salmon Salmo salar

The present study shows that permanent melanophore spot patterns in Atlantic salmon Salmo salar make it possible to use images of the operculum to keep track of individual fish over extended periods of their life history. Post‐smolt S. salar (n = 246) were initially photographed at an average mass of 98 g and again 10 months later after rearing in a sea cage, at an average mass of 3088 g. Spots that were present initially remained and were the most overt (largest) 10 months later, while new and less overt spots had developed. Visual recognition of spot size and position showed that fish with at least four initial spots were relatively easy to identify, while identifying fish with less than four spots could be challenging. An automatic image analysis method was developed and shows potential for fast match processing of large numbers of fish. The current findings promote visual recognition of opercular spots as a welfare‐friendly alternative to tagging in experiments involving salmonid fishes.     

Liver ultrastructure of juvenile Atlantic salmon (Salmo salar)

Light and transmission electron microscopy of the liver of juvenile Atlantic salmon (Salmo salar) reveals a tubular arrangement of parenchymal cells, with biliary passages typically located at the center of tubules. Hepatocytes generally contain a single nucleus surrounded by a cuff of rough endoplasmic reticulum (RER), with many round to elongate mitochondria associated with the perinuclear RER. Whereas glycogen deposits are common and usually lie at the cell periphery, parenchymal cells seldom contain lipid droplets. Golgi complexes and heterogeneous dense bodies also occur in many hepatocytes, often in close proximity to bile canaliculi. Numerous microvilli from hepatocytes extend into the subendothelial space of Disse, which is also the location of stellate fat-storing cells. Interhepatocytic macrophages, sometimes containing prominent phagolysosomes and residual bodies, are common in the liver. The intrahepatic biliary system consists of intercellular canaliculi, bile pre-ductules, ductules, and ducts. In contrast to some other teleosts, the liver of the Atlantic salmon contains no intracellular bile canaliculi or Kupffer cells. The hepatic endothelium, arterioles, and perivenous regions are also described.     

Phylogenetic position of a paramyxovirus from Atlantic salmon Salmo salar

A paramyxovirus has been isolated from Atlantic salmon Salmo salar suffering from epitheliocystis. This virus does not cause any mortality when used to challenge disease-free salmon, but has been associated with 2 cases of mortality in salmon farms in Norway. Atlantic salmon paramyxovirus (ASPV) has been suggested as a name for the virus. The ASP virus is a slow-growing virus in cell cultures (rainbow trout gill cells: RTgill-W1). Little is known about its importance and its phylogenetic position is uncertain. Hence, the need for a fast and sensitive diagnostic method for studying the prevalence of this virus in salmon farms and for more basic knowledge about its identity were the motivation for this study. A partial nucleotide sequence (816 bp) from the large protein (L protein) gene of the ASP virus has been sequenced from 2 different isolates. The putative amino acid sequence has been compared with the L protein of other paramyxoviruses. This sequence gives strong support to a relationship between the ASP virus and members of the subfamily Paramyxovirinae, genus Respirovirus.     

Naked DNA vaccination of Atlantic salmon Salmo salar against IHNV

A naked plasmid DNA encoding the glycoprotein (pCMV4-G) of a 1976 isolate of infectious hematopoietic necrosis virus (IHNV) obtained from steelhead Oncorhynchus mykiss was used to vaccinate Atlantic salmon Salmo salar against IHNV. Eight weeks post-vaccination the fish were challenged with a strain of IHNV originally isolated from farmed Atlantic salmon undergoing an epizootic. Fish injected with the glycoprotein-encoding plasmid were significantly (p < 0.05) protected against IHNV by both immersion and cohabitation challenge. Survivors of the first challenges were pooled and re-challenged by immersion 12 wk after the initial challenge. Significant (p < 0.05) protection was observed in all of the previously challenged groups including those receiving the complete vaccine. Fish injected with the glycoprotein-encoding plasmid produced low levels of virus-neutralizing antibodies prior to the first challenge. Neutralizing antibodies increased in all groups after exposure to the IHNV. Passive transfer of pooled sera from pCMV4-G vaccinates and IHN survivors provided relative survivals of 40 to 100% compared to fish injected with sera collected from fish immunized with control vaccines or left unhandled. In this study, DNA vaccination effectively protected Atlantic salmon smolts against challenges with IHNV.     

Biochemical genetics of the Atlantic salmon Salmo salar L.

In recent years, blood group and protein polymorphisms in Atlantic salmon have been investigated extensively with a view, primarily, to their use in identifying individuals of different spawning populations present in high seas fisheries. Erythrocyte antigens, haemoglobins, serum proteins and various tissue enzymes—mainly esterases and de-hydrogenases—have been studied by electrophoretic and immunological techniques. These studies are reviewed here for the first time.
Many of the protein systems exhibit multiple components and this fact, together with cytological evidence, indicates the occurrence of tetraploidy in the course of Salmonid evolution. The significance of a tetraploid origin in the evolution and ecological adaptation of Salmonids is discussed briefly.
Some protein systems studied exhibit phylogenetic variation, and analyses of phenotype ratios and allele frequencies indicate that the populations of different river systems are genetically distinct. Allele frequencies have not yet been shown to be stable from generation to generation however, and some of the factors likely to affect allele frequencies are discussed.
Different spawning populations can not be identified in high seas fisheries using these protein characters, although it may be possible to identify the continent of origin (N. America or Europe) of some individuals. Indeed, it has been proposed independently by two groups that North American and European populations of Atlantic salmon be assigned to different sub-species viz. S. s. americanus and S. s. europaeus respectively. The contradictory evidence on which these taxa are proposed is discussed, together with the evidence for other population groups proposed in the European part of the salmon's range. The possible role and future direction of studies on the biochemical genetics of salmon are outlined.     

Experimental infections of Atlantic salmon Salmo salar with Spironucleus barkhanus

Atlantic salmon Salmo salar L. (Salmonidae) were experimentally infected with Spironucleus barkhanus (Diplomonadida: Hexamitidae). Parasites were found in the blood 1 to 8 wk after infection, after which they disappeared from the blood and were found mainly in the internal organs (e.g. spleen and liver), eye socket or muscles. Mortality (38 out of 40 infected fish) occurred when fish had lesions in internal organs and/or on the body surface. Uninfected fish cohabiting with infected fish became infected after 4 wk, indicating direct transmission. There was no difference in susceptibility to spironucleosis between 3 different families of Atlantic salmon. All families developed the disease with a similar pattern of parasitaemia in the blood, similar clinical signs and gross pathology, and with very high mortality (29 out of 30). Clinical signs of systemic spironucleosis may include anemia, skin blisters, muscle ulcerations or unilateral exophthalmia. Gross pathologies include hemorrhaging of internal organs, splenomegaly or deformed (globulated) spleen, or granulomatous lesions in the spleen and liver.