Sample displacement chromatography of Atlantic Salmon (Salmo salar) thrombin

A modified method of sample displacement chromatography (SDC) was used to purify active salmon thrombin on a heparin-coupled matrix to near homogeneity in milligram amounts from 117 ml plasma. This was achieved by combining a low-pressure multi-column affinity chromatography system with non-homogenous sample application in the order of increasing affinity to Heparin Sepharose. The results suggest that this modified method could be useful in protein purification. Some characteristics of salmon thrombin are presented.     

The feeding behaviour of juvenile Atlantic salmon in relation to turbulent flow

The feeding behaviour of juvenile Atlantic salmon Salmo salar in the Sainte‐Marguerite River, Quebec, Canada, varied with the characteristics of turbulent flow. Simulations indicated that juveniles would decrease their swimming costs during attacks by 19·8% in low and by 31·1% in high turbulent conditions by initiating movements in low‐speed flow events. The real swimming costs did not differ from the swimming costs estimated for a situation where fish initiate their movements at randomly selected flow velocities. The juvenile Atlantic salmon did not seem to prefer low‐speed flow events when initiating their movements. The proportion of time used for movements by fish decreased with an increase in the mean and the s . d . of the flow velocity.     

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.     

Movement and habitat shift responses of juvenile Atlantic Salmon (Salmo salar) to annually permanent stream flooding

Reservoir formation in a river system changes a lotic environment to more lacustrine conditions, with impacts throughout the ecosystem. In this study, a river reach containing typical salmonid riffle/run habitat was flooded to create a large, deep pool from June to September in each of 3 years. We test the hypothesis that juvenile Atlantic salmon (Salmo salar) with their preference for run/riffle habitats will respond to the transformation to a lentic environment by moving into adjacent lotic environments. Movements of juvenile Atlantic salmon were monitored using a combination of biotelemetry (radio- and passive integrated transponder-tagging) and electrofishing. Results showed that no tracked fish moved away from the created pool habitat. Mass-specific growth rates showed the created pool habitat resulted in net growth of juveniles. The results confirm that fish may not immediately (i.e., at least for an approximate 2 months) respond to rapid, large-scale habitat alterations by moving to find similar habitat conditions outside the altered habitat. This is most probably related to plasticity of behavior and habitat use, and no change in biological conditions to a point that would negatively impact fish growth and survival, for example food availability, competition, or predation. The results also support the hypothesis that the relative importance of physical habitat variables is not universal among streams and populations, therefore limiting the value of applying standard habitat suitability criteria and use.     

Tissue Distribution of 14C-Diflubenzuron in Atlantic Salmon (Salmo salar)

Diflubenzuron is a potent inhibitor of chitin synthesis, with potential use against salmon lice infestations. The absorption, distribution and elimination of the substance in Atlantic salmon was examined after a single, oral dose of 75 mg/kg body weight. The kinetic properties were studied by whole-body autoradiography, liquid scintillation counting and thin layer chromatography, using a 14C-labelled isotope of the substance. The drug was poorly absorbed from the intestine, but reached a concentration of more than 4 µg/g in the mucus layer of the skin 2 days after administration. If maintained for several days, this concentration is probably sufficient to control all moulting stages of sea lice in Atlantic salmon. The main route of excretion was via the bile.     

N-Terminal Sequence and Main Characteristics of Atlantic Salmon (Salmo salar) Albumin

Atlantic salmon (Salmo salar) serum albumin was purified from plasma and its N-terminal sequence determined. Atlantic salmon albumin is the predominant plasma protein, negatively charged, at pH 8.6. Albumin was purified to >95% purity which yielded a single band on SDS-PAGE and agarose gel electrophoresis. The molecular weight of the purified albumin was approximately 6,5 kDa. The N-terminal sequence of Atlantic chinook salmon albumin was consistent with that predicted from its previously determined cDNA sequence and was identical to that of salmon (Oncorhynchus tshawytscha) albumin through the first 15 residues. However, the fact that the actual N-terminus was different from that predicted from cDNA sequence indicates that Atlantic salmon albumin, like chinook salmon albumin, lacks a propeptide.     

The hearing of the Atlantic Salmon, Salmo salar

The hearing of the salmon, Salmo salar L., was studied by means of a cardiac conditioning technique. Fish were trained to show a slowing of the heart, on hearing a sound, in anticipation of a mild electric shock applied later. The minimum sound level to which the fish would respond was determined for a range of pure tones, both in the sea, and in the laboratory. The fish responded only to low frequency tones (below 380 Hz), and particle motion, rather than sound pressure, proved to be the relevant stimulus. The sensitivity of the fish to sound was not affected by the level of sea noise under natural conditions but hearing is likely to be masked by ambient noise in a turbulent river. Sound measurements made in the River Dee, near Aberdeen, lead to the conclusion that salmon are unlikely to detect sounds originating in air, but that they are sensitive to substrate borne sounds. Compared with the carp and cod the hearing of the salmon is poor, and more like that of the perch and plaice.     

Cataract Development in Atlantic Salmon (Salmo salar L) in Fresh Water

Irreversible bilateral cataracts were diagnosed by slit-lamp biomicroscopy in 178 of 200 farm-raised Atlantic salmon (Salmo salar L) fed a standard diet over a five-month period. Initial changes were anterior polar opacities, progressing to involve both the anterior and posterior cortex before changes in the lens nucleus were seen. The lens changes were recorded and given scores according to the severity of the cataracts. At each of 3 samplings, after 2, 4 and 5 months, 200 fish were measured, weighed and examined by slit-lamp biomicroscopy. At all 3 samplings, there was a significant correlation between body length and both cataract incidence and cataract severity. There was also a significant correlation between body weight and cataract incidence and severity for the 2 last samplings. There was a significant correlation between K-factor as a measure of the shape of the fish, and both cataract incidence and severity, at all 3 samplings. Evaluation of specific growth rate in the periods between the examinations showed that the rapidly-growing fish were most susceptible to cataract formation. After cataract developed, however, the growth rate slowed. Follow-up examination of severely affected fish 3 months after transfer to sea water showed a normal cortical zone in the periphery of the lens in 24 out of 28 fish.     

The functional relationship between peak spring floods and survival and growth of juvenile Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta)

1. The effects of high spring floods on survival and growth of juvenile Atlantic Salmon, Salmo salar, and Brown Trout, Salmo trutta , are explored, using data from a long-term study in the River Saltdalselv, northern Norway. The flow regime in this river is typical for northern rivers.
2. There was considerable variation in year class strength of both species.
3. Mortality of Atlantic Salmon increased significantly in years with high discharge during the alevin stage as well as the first week after emergence. High discharge during the egg stage and more than 1 week after emergence seemed to be of minor importance. Water temperature at emergence was rather high (average 10·5 °C) and did not significantly affect year class strength.
4. Brown Trout emerged earlier than Atlantic Salmon at an average water temperature of 8·2 °C. Highest mortality was observed in years with low water temperatures at emergence as well as high discharge during the alevin stage.
5. For 1-year-old fish or older, the size of the spring peak flood did not influence mortality significantly.
6. Growth of Atlantic Salmon parr was diminished in years with a high peak spring flood. A similar effect on Brown Trout was not detected.     

The Thyrotropic Cell in the Atlantic Salmon,Salmo salar

The thyrotropin (TSH) producing cells are distributed in the rostral and proximal pars distalis. This cell type is the smallest and most infrequent cell of the adenohypophysis. Its cytology is similar to the smallest gonadotropic (GTH) cells although the two cell types can be separated by the size of the small secretory granules (diameter less than 200 nm) in the TSH cells. In presmolts and smolts the cells are more numerous than in parr and adult salmon and have cytological features indicating an increased activity. This was also the case after intraperitoneal injections of synthetic TRH. Antisera to carp GTH and salmon GTH cross-reacted with both the GTH and the TSH cells. Anti-human TSH cross-reacted only with the TSH cells which confirms the assumption of antigenic similarity between human and fish TSH.     

N‐Terminal Sequence and Main Characteristics of Atlantic Salmon (Salmo salar) Albumin

Abstract

Atlantic salmon (Salmo salar) serum albumin was purified from plasma and its N‐terminal sequence determined. Atlantic salmon albumin is the predominant plasma protein, negatively charged, at pH 8.6. Albumin was purified to >95% purity which yielded a single band on SDS‐PAGE and agarose gel electrophoresis. The molecular weight of the purified albumin was approximately 6,5 kDa. The N‐terminal sequence of Atlantic chinook salmon albumin was consistent with that predicted from its previously determined cDNA sequence and was identical to that of salmon (Oncorhynchus tshawytscha) albumin through the first 15 residues. However, the fact that the actual N‐terminus was different from that predicted from cDNA sequence indicates that Atlantic salmon albumin, like chinook salmon albumin, lacks a propeptide.     

Seasonal variation in the thermal performance of juvenile Atlantic salmon (Salmo salar)

1. Experimental data on the maximum growth and food consumption of winter‐acclimatised Atlantic salmon (Salmo salar) juveniles from three Norwegian rivers situated at 59 and 70°N were compared with predictions from published models of growth and food consumption of summer‐acclimatised fish from the same populations. 2. All winter‐acclimatised fish maintained positive growth and a substantial energy intake over the whole range of experimental temperature (1–6 °C). This contrasted with predictions from growth models based on summer acclimatised Atlantic salmon, where growth and energy intake ceased at approximately 5 °C. 3. Growth and food consumption varied significantly among populations. Winter‐acclimatised fish from a Northern population had a higher mass‐specific growth rate, higher energy intake and higher growth efficiency than southern populations, which is contrary to predictions from models developed using summer‐acclimatised salmon, where fish from the Northern population had the lowest growth efficiency. 4. The experiment provides evidence that thermal performance varies seasonally and suggests adaptation to the annual thermal regime.     

Differences in the energetic cost of swimming in turbulent flow between wild,farmed and domesticated juvenile Atlantic salmon Salmo salar

Domestication has been shown to have an effect on morphology and behaviour of Atlantic salmon (Salmo salar). We compared swimming costs of three groups of juvenile Atlantic salmon subject to different levels of domestication: (1) wild fish; (2) first generation farmed fish origination from wild genitors; and (2) seventh generation farmed fish originating from Norwegian aquaculture stocks. We assessed swimming costs under two types of turbulent flow (one mean flow velocity of 23 cm s^?1 and two standard deviations of flow velocity of 5 and 8 cm s^?1). Respirometry experiments were conducted with fish in a mass range of 5–15 g wet at a water temperature of 15° C. Our results confirm (1) that net swimming costs are affected by different levels of turbulence such that, for a given mean flow velocity, fish spent 1·5‐times more energy as turbulence increased, (2) that domesticated fish differed in their morphology (having deeper bodies and smaller fins) and in their net swimming costs (being up to 30·3% higher than for wild fish) and (3) that swimming cost models developed for farmed fish may be also be applied to wild fish in turbulent environments.     

Physiological seawater adaptation in juvenile Atlantic salmon (Salmo salar) autumn migrants

Summary

• 1 About 25 % of juvenile Atlantic salmon (Salmo salar) migrating downstream in the River Frome in southern England do so in the autumn rather than in the spring. Here, we examine the physiological status of these fish with regard to those features that adapt them to sea water during the parr–smolt transformation (i.e. gill Na⁺K⁺ ATPase activity; the number, size and type of chloride cells on the gill lamellae; salinity tolerance and relative plasma thyroid levels).
• 2 Autumn migrants, and those fish which subsequently reside in the tidal reaches during the winter, are not sufficiently physiologically adapted to permit permanent or early, entry into the marine environment.
• 3 It is not known what proportion of autumn migrating fish survive and return to spawn as adults. If significant numbers do return, however, the production from tidal reach habitats must be taken into account in the development of salmon stock management strategies, especially monitoring and assessment programmes, and in the evaluation of factors affecting stocks.

     

Age Structure,Changing Demography and Effective Population Size in Atlantic Salmon (Salmo salar)

Effective population size (N_e) is a central evolutionary concept, but its genetic estimation can be significantly complicated by age structure. Here we investigate N_e in Atlantic salmon (Salmo salar) populations that have undergone changes in demography and population dynamics, applying four different genetic estimators. For this purpose we use genetic data (14 microsatellite markers) from archived scale samples collected between 1951 and 2004. Through life table simulations we assess the genetic consequences of life history variation on N_e. Although variation in reproductive contribution by mature parr affects age structure, we find that its effect on N_e estimation may be relatively minor. A comparison of estimator models suggests that even low iteroparity may upwardly bias N_e estimates when ignored (semelparity assumed) and should thus empirically be accounted for. Our results indicate that N_e may have changed over time in relatively small populations, but otherwise remained stable. Our ability to detect changes in N_e in larger populations was, however, likely hindered by sampling limitations. An evaluation of N_e estimates in a demographic context suggests that life history diversity, density-dependent factors, and metapopulation dynamics may all affect the genetic stability of these populations.THE effective size of a population (N_e) is an evolutionary parameter that can be informative on the strength of stochastic evolutionary processes, the relevance of which relative to deterministic forces has been debated for decades (e.g., Lande 1988). Stochastic forces include environmental, demographic, and genetic components, the latter two of which are thought to be more prominent at reduced population size, with potentially detrimental consequences for average individual fitness and population persistence (Newman and Pilson 1997; Saccheri et al. 1998; Frankham 2005). The quantification of N_e in conservation programs is thus frequently advocated (e.g., Luikart and Cornuet 1998; Schwartz et al. 2007), although gene flow deserves equal consideration given its countering effects on genetic stochasticity (Frankham et al. 2003; Palstra and Ruzzante 2008).Effective population size is determined mainly by the lifetime reproductive success of individuals in a population (Wright 1938; Felsenstein 1971). Variance in reproductive success, sex ratio, and population size fluctuations can reduce N_e below census population size (Frankham 1995). Given the difficulty in directly estimating N_e through quantification of these demographic factors (reviewed by Caballero 1994), efforts have been directed at inferring N_e indirectly through measurement of its genetic consequences (see Leberg 2005, Wang 2005, and Palstra and Ruzzante 2008 for reviews). Studies employing this approach have quantified historical levels of genetic diversity and genetic threats to population persistence (e.g., Nielsen et al. 1999b; Miller and Waits 2003; Johnson et al. 2004). N_e has been extensively studied in (commercially important) fish species, due to the common availability of collections of archived samples that facilitate genetic estimation using the temporal method (e.g., Hauser et al. 2002; Shrimpton and Heath 2003; Gomez-Uchida and Banks 2006; Saillant and Gold 2006).Most models relating N_e to a population''s genetic behavior make simplifying assumptions regarding population dynamics. Chiefly among these is the assumption of discrete generations, frequently violated in practice given that most natural populations are age structured with overlapping generations. Here, theoretical predictions still apply, provided that population size and age structure are constant (Felsenstein 1971; Hill 1972). Ignored age structure can introduce bias into temporal genetic methods for the estimation of N_e, especially for samples separated by time spans that are short relative to generation interval (Jorde and Ryman 1995; Waples and Yokota 2007; Palstra and Ruzzante 2008). Moreover, estimation methods that do account for age structure (e.g., Jorde and Ryman 1995) still assume this structure to be constant. Population dynamics will, however, likely be altered as population size changes, thus making precise quantifications of the genetic consequences of acute population declines difficult (Nunney 1993; Engen et al. 2005; Waples and Yokota 2007). This problem may be particularly relevant when declines are driven by anthropogenic impacts, such as selective harvesting regimes, that can affect age structure and N_e simultaneously (Ryman et al. 1981; Allendorf et al. 2008). Demographic changes thus have broad conservation implications, as they can affect a population''s sensitivity to environmental stochasticity and years of poor recruitment (Warner and Chesson 1985; Ellner and Hairston 1994; Gaggiotti and Vetter 1999). Consequently, although there is an urgent need to elucidate the genetic consequences of population declines, relatively little is understood about the behavior of N_e when population dynamics change (but see Engen et al. 2005, 2007).Here we focus on age structure and N_e in Atlantic salmon (Salmo salar) river populations in Newfoundland and Labrador. The freshwater habitat in this part of the species'' distribution range is relatively pristine (Parrish et al. 1998), yet Atlantic salmon in this area have experienced demographic declines, associated with a commercial marine fishery, characterized by high exploitation rates (40–80% of anadromous runs; Dempson et al. 2001). A fishery moratorium was declared in 1992, with rivers displaying differential recovery patterns since then (Dempson et al. 2004b), suggesting a geographically variable impact of deterministic and stochastic factors, possibly including genetics. An evaluation of those genetic consequences thus requires accounting for potential changes in population dynamics as well as in life history. Life history in Atlantic salmon can be highly versatile (Fleming 1996; Hutchings and Jones 1998; Fleming and Reynolds 2004), as exemplified by the high variation in age-at-maturity displayed among and within populations (Hutchings and Jones 1998), partly reflecting high phenotypic plasticity (Hutchings 2004). This diversity is particularly evident in the reproductive biology of males, which can mature as parr during juvenile freshwater stages (Jones and King 1952; Fleming and Reynolds 2004) and/or at various ages as anadromous individuals, when returning to spawn in freshwater from ocean migration. Variability in life history strategies is further augmented by iteroparity, which can be viewed as a bet-hedging strategy to deal with environmental uncertainty (e.g., Orzack and Tuljapurkar 1989; Fleming and Reynolds 2004). Life history diversity and plasticity may allow salmonid fish populations to alter and optimize their life history under changing demography and population dynamics, potentially acting to stabilize N_e. Reduced variance in individual reproductive success at low breeder abundance (genetic compensation) will achieve similar effects and might be a realistic aspect of salmonid breeding systems (Ardren and Kapuscinski 2003; Fraser et al. 2007b). Little is currently known about the relationships between life history plasticity, demographic change and N_e, partly due to scarcity of the multivariate data required for these analyses.Our objective in this article is twofold. First, we use demographic data for rivers in Newfoundland to quantify how life history variation influences age structure in Atlantic salmon and hence N_e and its empirical estimation from genetic data. We find that variation in reproductive contribution by mature parr has a much smaller effect on the estimation of N_e than is often assumed. Second, we use temporal genetic data to estimate N_e and quantify the genetic consequences of demographic changes. We attempt to account for potential sources of bias, associated with (changes in) age structure and life history, by using four different analytical models to estimate N_e: a single-sample estimator using the linkage disequilibrium method (Hill 1981), the temporal model assuming discrete generations (Nei and Tajima 1981; Waples 1989), and two temporal models for species with overlapping generations (Waples 1990a,b; Jorde and Ryman 1995) that differ principally in assumptions regarding iteroparity. A comparison of results from these different estimators suggests that iteroparity may often warrant analytical consideration, even when it is presumably low. Although sometimes limited by statistical power, a quantification and comparison of temporal changes in N_e among river populations suggests a more prominent impact of demographic changes on N_e in relatively small river populations.     

Spawning behaviour of a farmed escaped female Atlantic salmon (Salmo salar)

Excavation of stranded redds revealed differences in spawning behaviour between farmed and wild Atlantic salmon. The redd of a farmed fish contained more egg pockets (nine v . average of two) and fewer eggs per pocket (averages: 459 v . 707). No other pocket measures differed.