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Landlocked Atlantic salmon (ouananiche, Salmo salar) spawning migration timing varies throughout its range and is influenced by a variety of environmental variables. This study examined the spawning migration time of landlocked Atlantic salmon in a small (4 ha) constructed stream linked to a large reservoir (32,600 ha) in Newfoundland, Canada. Salmon use of the stream was passively monitored using Passive Integrated Transponder ( PIT) Tags from 2006 to 2012. Of the salmon tagged throughout the reservoir, 48% entered the stream during the spawning season and remained there for 18-36 days from late September to November before they returned to the reservoir. Most fish entered the stream at dusk (32%). The lunar cycle influenced the timing of migration each year. Mean stream discharge (cubic metres per second) influenced migration timing in some years, and water temperature appeared to have minimal impact on migration timing. Twenty per cent of fish migrated to the stream in multiple years and 51% of these individuals appeared to use the stream on a biennial or alternate year cycle. These results demonstrate that small constructed streams can attract salmon from throughout a large reservoir and can provide valuable habitat in areas where spawning habitat is limited. [ABSTRACT FROM AUTHOR]

The behavior of early (June-July) and late (August-September) migrating, adult Atlantic salmon, in The River Klarälven, Sweden, was analyzed using radio telemetry. River Klarälven is a regulated river without functioning fishways, instead upstream migrating salmon are trapped and trucked past eight hydropower plants before released back to the river. We distinguished two parts of the spawning migration, that is, one part being the migration from the place where the fish was released to the spawning grounds. The other part was a holding phase on the spawning grounds with little or no movements before spawning. The late salmon spent less of their total time on holding, 36.2%, and more on migration, 63.8%, compared with early migrating salmon, which distributed their time rather evenly between migration, 47.5%, and holding, 52.5%. In total, early salmon used 30% more time migrating and 156% more time holding than late salmon. Some Atlantic salmon (Salmo salar) fell back over the hydropower plant after release and got excluded from spawning. The fallback rates of transported, tagged spawners were higher in the early than in the late group in both years. The fallback rate in 2012 was 42.8% of the early group and 15.1% in the late. In 2013, there were 51.7 % fallbacks in the early group and 3.4% in the late. The salmon fell back on average 9 days after being released in 2012 and 16 days in 2013. A high mean daily discharge on the day of release increased the probability of becoming a fallback. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The dynamics of fatty acid composition have been studied in differently aged salmon juveniles (0+, 1+, 2+ parrs and 3+ smolts) inhabiting two biotopes of the Varzuga River (the White Sea basin) differing in ecological conditions. Differences in the levels of linoleic (18:2n-6), linolenic (18:3n-3), and oleic (18:1n-9) acids have been revealed. It has also been shown that 3+ smolts have an increased content of long-chain fatty acids-arachidonic (20:4n-6), eicosapentaenoic (20:5n-3), and docosahexaenoic (22:6n-3)-characteristic of the composition of marine-type lipids. [ABSTRACT FROM AUTHOR]

Th article discusses the histopatholgy, immunohistochemistry, and gross pathology associated with Pasteurella piscicida (PP) as the causative agent in outbreaks of disease in Atlantic salmon. It states that the four isolates of the PP are the same except for the 97A1which showed some differences in 16S rRNA gene sequence. The hypothesis on the possible source of the P. skyensis in infected Atlantic salmon from mammals either from migratory or local animals, is cited.

Abstract: The migratory timing and behaviour of wild Atlantic salmon smolts leaving their natal stream was determined using a passive integrated transponder (PIT) antennae system at a study site on a tributary of the River Itchen, England. Experiments compared the downstream migration of smolts under natural control conditions (2000–2006) with two years (2008 and 2009) when the main downstream exit of the study site was subject to street-lit conditions every alternate night (maximum light intensity measured at the stream surface=14lx). Migration of smolts under control conditions was significantly (p <0.01, n=170) correlated with sunset. By contrast, street lighting resulted in the timing of migration being random (p =0.11, n=7; p =0.76, n=34, respectively) with respect to time of day. Furthermore, migration of smolts was significantly (p =0.01, n=19) correlated with the time of sunset for fish migrating when the lamp had been off, but random (p =0.36, n=22) when the lamp had been on (2008 and 2009 data, combined). This alteration in migratory behaviour due to street lighting may impact fitness. [Copyright &y& Elsevier]

Soybean meal (SBM) induces enteritis in the distal intestine of Atlantic salmon. The present study assesses the effects of SBM concentrations on the kinetics of the enteritis process. Fish of 300 g, kept at 12 °C, were fed diets with different SBM inclusions: 0%, 10% and 20% SBM for 57 days. Samples of the distal intestine of five fish per treatment were taken for histological and electron microscopical analysis. A semi-quantitative scoring system was used to assess the degree of the morphological changes induced by SBM feeding in the distal intestinal epithelium. The first signs of enteritis appeared earlier in the salmon fed the 20SBM diet than in those fed the 10SBM diet. Thereafter, the condition increased steadily, displaying no signs of recovery. Furthermore, at the lower concentration, the process marking the onset of enteritis began more gradually than at the higher concentration and it displayed a tendency to stabilize after 13–20 days of continuous feeding. Electron microscopy indicated that the endocytosis process was hampered at day 3 of 20SBM and at 7 days of 10SBM. Furthermore, a strong reduction of microvilli was already evident after 7 days of 20SBM feeding, thus indicating a decreased uptake capacity of the distal enterocytes. In addition, transformation and migration of eosinophilic granulocytes was observed, which, in combination with the lysozyme C immunoreactivity supports their protective role during the inflammatory process in the distal gut of Atlantic salmon. It can be concluded that the severity of enteritis and its kinetics are concentration-dependent, showing no signs of recovery during feeding with diets containing SBM. [ABSTRACT FROM AUTHOR]

This study investigates the benefits of using prevalence as a summary measure of sea lice infestation on farmed Atlantic salmon, Salmo salar L. Aspects such as sampling effort, the relationship between abundance and prevalence arising from the negative binomial distribution, and how this relationship can be used to indicate the degree of aggregation of lice on a site at a given time point are discussed. As a case study, data were drawn from over 50 commercial Atlantic salmon farms on the west coast of Scotland between 2002 and 2006. Descriptive statistics and formal analysis using a linear modelling technique identified significant variations in sea lice prevalence across year class, region and season. Supporting evidence of a functional relationship between prevalence and abundance of sea lice is provided, which is explained through the negative binomial distribution. [ABSTRACT FROM AUTHOR]

Life-history studies comparing landlocked versus diadromous populations reveal factors associated with life-history evolution under different scenarios. We describe several aspects of spawning and development of landlocked Aplochiton zebra in Patagonia (Argentina) based on the presence of eggs, the gonadal development, the analysis of otolith daily growth increments validated by tetracycline marking experiments, and the analysis of standard length frequencies. Among Patagonian galaxiids, A. zebra showed intermediate size and age at first maturity and high fecundity, with vitellogenic oocytes covered with short chorionic filaments. Free embryos of A. zebra were larger than those of Galaxias maculatus and Galaxias platei. This information is particularly significant for conservational purposes when we consider the reduced distribution of landlocked populations of the species and the risks imposed by salmonid introduction. [ABSTRACT FROM AUTHOR]

Abstract: The present study compares developmental changes in plasma levels of growth hormone (GH), insulin-like growth factor I (IGF-I) and cortisol, and mRNA levels of their receptors and the prolactin receptor (PRLR) in the gill of anadromous and landlocked Atlantic salmon during the spring parr-smolt transformation (smoltification) period and following four days and one month seawater (SW) acclimation. Plasma GH and gill GH receptor (GHR) mRNA levels increased continuously during the spring smoltification period in the anadromous, but not in landlocked salmon. There were no differences in plasma IGF-I levels between strains, or any increase during smoltification. Gill IGF-I and IGF-I receptor (IGF-IR) mRNA levels increased in anadromous salmon during smoltification, with no changes observed in landlocked fish. Gill PRLR mRNA levels remained stable in both strains during spring. Plasma cortisol levels in anadromous salmon increased 5-fold in May and June, but not in landlocked salmon. Gill glucocorticoid receptor (GR) mRNA levels were elevated in both strains at the time of peak smoltification in anadromous salmon, while mineralocorticoid receptor (MR) mRNA levels remained stable. Only anadromous salmon showed an increase of gill 11β-hydroxysteroid dehydrogenase type-2 (11β-HSD2) mRNA levels in May. GH and gill GHR mRNA levels increased in both strains following four days of SW exposure in mid-May, whereas only the anadromous salmon displayed elevated plasma GH and GHR mRNA after one month in SW. Plasma IGF-I increased after four days in SW in both strains, decreasing in both strains after one month in SW. Gill IGF-I mRNA levels were only increased in landlocked salmon after 4days in SW. Gill IGF-IR mRNA levels in SW did not differ from FW levels in either strain. Gill PRLR mRNA did not change after four days of SW exposure, and decreased in both strains after one month in SW. Plasma cortisol levels did not change following SW exposure in either strain. Gill GR, 11β-HSD2 and MR mRNA levels increased after four days in SW in both strains, whereas only the anadromous strain maintained elevated gill GR and 11β-HSD2 mRNA levels after one month in SW. The results indicate that hormones and receptors of the GH and cortisol axes are present at significantly lower levels during spring development and SW acclimation in landlocked relative to anadromous salmon. These findings suggest that attenuation of GH and cortisol axes may, at least partially, result in reduced preparatory upregulation of key gill ion-secretory proteins, possibly a result of reduced selection pressure for marine adaptations in landlocked salmon. [Copyright &y& Elsevier]

Abstract: Net deformations of sea-cages in two full-scale commercial Atlantic salmon (Salmo salar) farms (Varaldsøy, Norway, Hestur, Faroe Islands) were determined in relation to incoming currents of varying velocities. Ambient currents were measured with acoustic current meters, and net deformation behaviour and cage volume reductions were found by using depth sensors (pressure sensors) placed on strategic locations at the net cage. Cages deformed in current flow largely through lifting of the bottom netting and deformation of the front and back walls. Currents and therefore net volume reductions differed between the two farms: at Varaldsøy, the most critical current/deformation combination was 0.13ms−1 and an estimated 20% cage volume reduction, while at Hestur, current speeds of 0.35ms−1 caused a corresponding 40% cage volume reduction. Substantial net deformation and cage volume reductions may have significant implications for both fish production and welfare. Development of a real time net volume indicator could assist farmers in maintaining adequate cage volumes for optimal production and serve as an indicator of the optimal timing for net replacement if biofouling levels contribute significantly to deformation. [Copyright &y& Elsevier]

Abstract: Pathogenic saprolegniaceae species are among the major disease-causing agents in farmed salmonids and in freshwater fish in general. Recent studies have used high-throughput cDNA-based methods to identify new potential actors of fish defence systems against various bacteria and viruses. However, the response of fish to fungal or fungus-like pathogens is still poorly documented. Here, we used a 16,006-gene salmonid cDNA microarray to identify genes which transcription levels are modified in juvenile Atlantic salmon (Salmo salar) affected with saprolegniasis compared to healthy fish from the same families. Our results confirmed the importance of non-specific immunity in the response of fish to saprolegniaceae infections and identified both similarities and differences in their genome-wide transcriptional response to oomycetes compared with their responses to bacterial or viral infections. Moreover, several clones with no known homologues were shown to be over-transcribed in infected fish. These may represent as yet unidentified immune-relevant genes in fish. [Copyright &y& Elsevier]

Many prey fishes rely on damage-released chemical alarm cues to detect and avoid predators. The ability to use these cues has been shown to confer considerable survival benefits to individuals. While several laboratory studies and a single field study have demonstrated that an ambient pH of 6.0 impairs fishes in their ability to detect these alarm cues, no study had yet compared the response to alarm cue exposures across populations residing in multiple streams of a different acidity level. In our study, we conducted live behavioural observations in five nursery streams, ranging in pH from 5.71 to 7.49 on two age classes (young of the year and parr) of wild juvenile Atlantic salmon (Salmo salar). We aimed to assess if the detection of these chemical alarm cues was constantly dependant on the ambient pH or if variations in the detection occurred among populations of the different streams regardless of the ambient acidity level. Our results demonstrated that salmon present in any acidic stream did not respond to alarm cues, while those in neutral streams exhibited typical alarm responses. [ABSTRACT FROM AUTHOR]

Landlocked Arctic charr (Salvelinus alpinus) populations in sub-Arctic and Arctic Greenland lakes were sampled with multi-mesh-sized survey gillnets. The study covered a range of small shallow lakes (0.01 km2, maximum depth <3.3 m) to large deep lakes (43 km2, maximum depth >200 m). Arctic charr were found in one to three different forms in lakes with maximum depths >3 m. A dwarf form occurred in all lakes inhabited by Arctic charr and was the only form in lakes with maximum depths <8 m. In deeper lakes with maximum depths >20 m and a surface area <0.5 km2, larger charr were found, although in low numbers, the length-frequency distribution being unimodal with a tail towards large sizes. In lakes with a maximum depth >20 m, large-sized charr were more abundant, and the length-frequency distribution of the population was bimodal, with a first mode around 10–12 cm and a second mode around 26–37 cm. In a single large and deep lake, a distinct medium-sized pelagic zooplankton-eating charr form occurred. Maximum size of individual charr was significantly positively correlated with lake maximum depth and volume, and the mean size of large-sized charr was significantly positively correlated with lake volume. Our study indicates that the charr population structure became more complex with increasing lake size. Moreover, the population structure seemed to be influenced by lake-water transparency and the presence or absence of three-spined stickleback (Gasterosteus aculeatus). [ABSTRACT FROM AUTHOR]

Paired releases of Carlin tagged fish were carried out in the river Kokemäenjoki, Bothnian Sea, in 1991–1993, to compare the survival and migration of Atlantic salmon (Salmo salar L.) smolts released at two different sites, off the estuary and at Nakkila, 55 km upstream. The eight different smolt groups, divided between the two sites, ranged in mean weight from 27 g (1 yr) to 260 g (2 yr). The size of the smolt groups were planned according to previous experience of the expected rate of recapture to allow the detection of a deviation of 20–25% from the initial 50:50 (coast:river) stocking ratio at a 5% significance level and 90% power, which requires 279 and 180 recaptures for each group, respectively. A 25% deviation corresponds to 40% mortality/55 km of river migration, which is somewhat less than reported in the literature. In all, 20 000 smolts were released. [ABSTRACT FROM PUBLISHER]