Characterization of a New HpaI Centromeric Satellite DNA in Salmo salar

A highly repeated HpaI DNA family was revealed in Atlantic salmon (Salmo salar) and analyzed by Southern blotting and fluorescence in situ hybridization (FISH). In this report, we describe the nucleotide sequence, genomic structure and chromosomal localization of this HpaI repeat. This novel satellite appeared tandemly arrayed and located at centromeric areas of three acrocentric chromosome pairs as evidenced by FISH. The sequence was characterized by a high AT content (63%), a short consensus motif (A/T)(G/C)AAA(T/C) similar to other centromeric satellites motifs, and by short AT enriched stretches. The presence of this sequence in other salmonid species was also tested by Southern blot hybridization and used to analyze its evolution within this group.     

The production of gynogenetic Atlantic salmon,Salmo salar L.

The production of Atlantic salmon gynogenomes by the combined use of a novel method for sperm irradiation and differently timed high hydrostatic pressure shocks is described. Sperm solutions were exposed to UV irradiation in a temperature-controlled flow-through device. Eggs fertilised with such sperm were exposed to shocks of 9500 psi at 30 min or approximately 7 h after fertilisation in order to produce meiotic and mitotic gynogenomes respectively. Yields of meiotic gynogenomes were generally high (up to 95%); those of mitotic gynogenomes were lower (range 2–20%). Analyses of the offspring by ploidy status and fingerprinting confirmed their gynogenetic origin. Small numbers of mitotic gynogenetic fish were grown on for 2 years in fresh and salt water. S1/S2 ratios were lower in gynogenetic fish and mean age at maturity was greater. Of the presumptive gynogenetic fish subjected to destructive sampling (n = 87) all were female.     

Major histocompatibility polymorphism associated with resistance towards amoebic gill disease in Atlantic salmon (Salmo salar L.)

The association between major histocompatibility (MH) polymorphism and the severity of infection by amoebic gill disease (AGD) was investigated across 30 full sibling families of Atlantic salmon. Individuals were challenged with AGD for 19days and then their severity of infection scored by histopathological examination of the gills. Fish were then genotyped for the MH class I (Sasa-UBA) and MH class II alpha (Sasa-DAA) genes using polymorphic repeats embedded within the 3' untranslated regions of the Sasa-UBA and Sasa-DAA genes. High variation in the severity of infection was observed across the sample material, ranging from 0% to 85% gill filaments infected. In total, seven Sasa-DAA-3UTR and ten Sasa-UBA-3UTR marker alleles were identified across the 30 families. A significant association between the marker allele Sasa-DAA-3UTR 239 and a reduction in AGD severity was detected. There was also a significant association found between AGD severity and the presence of two Sasa-DAA-3UTR genotypes. While the associations between MH allele/genotypes and AGD severity reported herein may be statistically significant, the small sample sizes observed for some alleles and genotypes means these associations should be considered as suggestive and future research is required to verify their biological significance.     

A population analysis of Robertsonian and Ag-NOR polymorphisms in brown trout (Salmo trutta)

An analysis of Robertsonian polymorphism and variation in the number of active NORs has been carried out in several populations of brown trout (Salmo trutta) from Northwestern Spain. The karyotype of this species appears to be soundly established, and essentially no variation has been found in chromosome number. Interindividual and interpopulation variation in arm number was detected, with figures ranging between 100 and 102 among individuals, and between 100.10 and 100.80 among populations. This variation in arm number is solely attributable to the polymorphism of the short arm of the main NOR-bearing pair 11, which can appear from acrocentric to metacentric in different individuals. Most populations analyzed showed the standard distribution of active NORs previously observed in this species. The Miño drainage basin, and specially the Chamoso population, showed a multi-chromosomal distribution of active NORs, with several new locations, always telomeric. In most cases no concordance was observed between previously detected rDNA sites in S. trutta and the new Ag-NOR locations. This fact suggests a transposition mechanism rather than an activation of silent rDNA sites to explain this multichromosomal NOR pattern.     

Enkephalin-immunoreactive cells in the mesencephalic tegmentum project to the optic tectum of the teleosts Salmo gairdneri and Salmo salar

Summary Immunocytochemistry using antibodies against Met-enkephalin and Leu-enkephalin has demonstrated a group of large enkephalin-immunoreactive neurons in the nucleus of the rostral mesencephalic tegmentum (mRMT) of two teleost fish, Salmo gairdneri and Salmo salar. Injections of cobalt-lysine in the medial optic tectum retrogradely labeled the above group of tegmental neurons. Tegmental neurons were labeled only ipsilaterally to the injection site. This indicates that enkephalinergic neurons in the nRMT project to the optic tectum, and that at least some of the enkephalinergic axons observed in the optic tectum belong to a tegmento-tectal pathway. Comparable enkephalinergic pathways have been described in reptiles and birds, where pretectal-mesencephalic nuclei contribute to the enkephalin-containing fibers that project to the optic tectum.     

A triose-phosphate isomerase polymorphism in the Atlantic salmonSalmo salar L.

Atlantic salmon,Salmo salar L., from four European locations show allelic variation at one of three triose-phosphate isomerase (TPI) loci (TPI-3*) when separated on horizontal starch gel electrophoresis, using either eye or liver extracts. Two common alleles (*100 and*103) and one rare allele (*97) segregate atTPI-3* with unambiguous typing being possible by observing the interlocus heterodimers. Family studies demonstrate thatTPI-3* 100 and*103 are of autosomal location and are inherited in a Mendelian fashion.TPI-3* variation can also be typed in adipose fin tissue, allowing nondestructive tissue sampling. Three loci are also active in brown trout,Salmo trutta, with two individuals being homozygous forTPI-3*, as are a small number ofS. salar from eastern Canada. The presence of this additional variable allozyme locus inS. salar is important, since genetic studies in that species have been limited by the low level of allozyme variability detectable.     

Renal,respiratory and ionic regulation in Atlantic salmon (Salmo salar L.) kelts following transfer from fresh water to seawater

Summary Atlantic salmon may return to the sea after spawning in fresh water. These fish, known as kelts, reportedly show a limited ability to hypoosmoregulate. However, this study shows that fresh-water-adapted kelts exposed to seawater demonstrate rapid adaptation (within 48 h) in osmoregulatory parameters to values characteristic of seawater-adapted salmonids. The urine flow rate falls from 1.2 to 0.2 ml·kg^-1·h^-1 within 24 h. Over the same period, urine osmolality increases from 48 mosmol·kg^-1 to become isosmotic with the plasma, and Mg²⁺ secretion by the kidney tubules elevates the urine concentration from 0.5 to 100 mmol·l^-1. As is characteristic for marine teleosts, kelts drink seawater and process the ingested water in the gut to replace body water lost by osmosis to the hyperosmotic medium. Seawater exposure causes a marked hypoxia, arterial oxygen tension falling by 43% within minutes and persisting for at least 4 days at this low level. This is associated with large changes in blood pH and acid-base balance. The physiological mechanisms involved in adaptation to a hyperosmotic external medium are discussed, and the osmoregulatory capacity of kelts is compared with that of salmon at other stages of the life cycle.Abbreviations FW fresh water - GFR glomerular filtration rate - Hb haemoglobin - Hct haematocrit - MCHC mean cell haemoglobin concentration - pH_a pH in arterial blood - P _aO₂ partial pressure of oxygen in arterial blood - SEM standard error of mean - SW seawater - UFR urine flow rate     

Diel activity pattern of juvenile Atlantic salmon (Salmo salar) in early and late winter

Radiotelemetry was used to investigate the diel activity pattern of juvenile Atlantic salmon (Salmo salar) in early and late winter. Fish were active throughout the diel cycle. However, there was significantly less daytime than nighttime movement and movement declined significantly with increasing fork length. Maximizing winter growth rate, through an overall increase in foraging activity, may reduce the risk of starvation in smaller fish. The results of the present study provide evidence that the activity patterns of juvenile salmonids are quite complex and support the suggestion that individual variation in activity patterns are, at least, partially driven by body size.     

First access to territorial space and exposure to strong predation pressure: A conflict in early emerging Atlantic salmon (Salmo salar L.) fry

Summary This work aimed to elucidate conflicting factors that may explain the narrow and synchronous emergence in salmonids. Fry are highly vulnerable to predation and stand a better chance of surviving if they emerge synchronously. On the other hand, fry that leave the gravel first should increase their chance of obtaining one of the limited number of feeding territories. The risk involved in early emergence for Atlantic salmon fry was evaluated by exposing them to predatorySalmo trutta. Yolk sac alevins were incubated in an artificial redd in order to catch them by their time of emergence. Early-, peak- and late-emerging fry were then successively marked and transferred to flume tanks in which the predators were either present from the start or not introduced until all fry had been added. When the predators were initially present, the predation pressure differed depending on the time of fry emergence, resulting in survival rates of 11.6, 44.9 and 51% in early-, peak- and late-emerging fry, respectively. By assuming that the predation rate of the three emergence groups was dependent both on time of emergence and fry density the survival rates were calculated to be 7.5, 41.1 and 53.5% in groups I, II and III, respectively. These figures corresponded well to the observed rates. When the predators were added after completed emergence the resulting survival rates were 56.9, 39.7 and 25.2% in early-, peak- and late-emerging fry, respectively. Thus, predation after complete emergence gave a survival probability that varied across the three emergence-date groups, despite being exposed to a predator during the same number of days. The presence of fish predators in combination with a limited territorial space seems to make both early and late emergence hazardous and favours synchronous swimming movements.     

Colocalization of neuropeptide Y (NPY)-like and FMRFamide-like immunoreactivities in the brain of the Atlantic salmon (Salmo salar)

Summary The colocalization of the peptides neuropeptide Y (NPY) and Phe-Met-Arg-Phe-NH₂ (FMRFamide) in the brain of the Atlantic salmon was investigated with double immunofluorescence labeling and peroxidase-antiperoxidase immunocytochemical techniques. Colocalization of NPY-like and FMRE amide-like immunoreactivities was observed in neuronal cell bodies and fibers in four brain regions: in the lateral and commissural nuclei of the area ventralis telencephali, in the nucleus ventromedialis thalami, in the laminar nucleus of the mesencephalic tegmentum, and in a group of small neurons situated among the large catecholaminergic neurons in the isthmal region of the brainstem. All cell bodies in these nuclei were immunoreactive to both NPY and FMRF. We consistently observed larger numbers of FMRF-immunoreactive than NPY-immunoreactive fibers. In the nucleus ventromedialis thalami NPY- and FMRFamide-like immunoreactivities were colocalized in cerebrospinal fluid (CSF)-contacting neurons. NPY-immunoreactive, but not FMRF-immunoreactive, neurons were found in the stratum periventriculare of the optic tectum, and at the ventral border of the nucleus habenularis (adjacent to the nucleus dorsolateralis thalami). Neurons belonging to the nucleus of the nervus terminalis were FMRF-immunoreactive but not NPY-immunoreactive. The differential labeling indicates, as do our cross-absorption experiments, that the NPY and FMRFamide antisera recognize different epitopes. Thus, it is probable that NPY-like and FMRFamide-like substances occur in the same neurons in some brain regions.     

Mate choice for major histocompatibility complex genetic divergence as a bet-hedging strategy in the Atlantic salmon (Salmo salar)

Major histocompatibility complex (MHC)-dependent mating preferences have been observed across vertebrate taxa and these preferences are expected to promote offspring disease resistance and ultimately, viability. However, little empirical evidence linking MHC-dependent mate choice and fitness is available, particularly in wild populations. Here, we explore the adaptive potential of previously observed patterns of MHC-dependent mate choice in a wild population of Atlantic salmon (Salmo salar) in Québec, Canada, by examining the relationship between MHC genetic variation and adult reproductive success and offspring survival over 3 years of study. While Atlantic salmon choose their mates in order to increase MHC diversity in offspring, adult reproductive success was in fact maximized between pairs exhibiting an intermediate level of MHC dissimilarity. Moreover, patterns of offspring survival between years 0+ and 1+, and 1+ and 2+ and population genetic structure at the MHC locus relative to microsatellite loci indicate that strong temporal variation in selection is likely to be operating on the MHC. We interpret MHC-dependent mate choice for diversity as a likely bet-hedging strategy that maximizes parental fitness in the face of temporally variable and unpredictable natural selection pressures.     

Studies on the alteration of chromosome copy number and cell division potential in a dnaA mutant of Escherichia coli

Summary The dnaA167 mutant of Escherichia coli, N167, maintains, on the average, two replicating chromosomes per cell at the perimissive growth temperature of 30°C and only one per cell at the higher permissive growth temperature of 38°C. When the growth temperature of this mutant is changed from 30° to 38°C the cells rapidly readjust their chromosome copy number from two to one. I have examined the kinetics of this transition with reference to DNA replication and cell division. My results indicate that this mutant uncouples cell division from chromosome duplication to achieve the appropriate copy number, suggesting that the dnaA gene product may be involved in the coordination between these two cellular events.     

Spatial and temporal variation of genetic diversity and estimation of effective population sizes in Atlantic salmon (Salmo salar, L.) populations from Asturias (Northern Spain) using microsatellites

Rivers in Asturias (northern Spain) constitute the southern limit of the distribution of Atlantic salmon (Salmo salar L.) in Europe, a biological resource facing one of the more serious challenges for conservation today. In this work, eight microsatellite loci have been used to analyse samples collected in 1993 and 1999 from four Asturian rivers (Esva, Narcea, Sella, and Cares), obtaining information about the temporal and the spatial genetic variation in these populations and, in addition, estimations of their effective population sizes. The temporal analysis revealed a general decrease in all the estimated genetic variability parameters when samples from 1993 (mean A ₍₁₉₉₃₎ = 6.47, mean H _O(1993) = 0.472, mean H _E(1993) = 0.530) were compared with those obtained in 1999 (mean A ₍₁₉₉₉₎ = 6.16, mean H _O(1999) = 0.460, mean H _E(1999) = 0.490). This reduction was particularly notable for the case of the Esva river. Our results pointed to a pattern of spatial genetic differentiation inside the Asturian region (F _{ST (1993)} = 0.016 P < 0.01; F _{ST (1999)} = 0.023 P < 0.01). Using the standard Temporal Method we found estimates of N _e^{^} _(Esva) = 75.1 (33.2–267.2); N _e^{^} _(Cares) = 96.6 (40.0–507.5), N _e^{^} _(Sella) = 106.5 (39.1–9396.4) and N _e^{^} _(Narcea) = 113.9 (42.0–3693.3). The use of likelihood-based methods for the N _e^{^} estimations improved the results (smaller CIs) for the Esva and Cares rivers (N _e^{^} _(Esva) = 63.9 (32.3–165.3); N _e^{^} _(Cares) = 76.4 (38.8–202.0) using a Maximum likelihood approach) and suggested the presence of larger populations for the Sella and Narcea rivers (N _e^{^}≈200). These results showed that the Asturian Atlantic salmon populations (in particular Esva and Cares river populations) could be close to the conservation genetic borderline for avoiding inbreeding depression although we discuss some implications of the analysis of temporal genetic change in populations with overlapping generations.     

Post-thawed motility and fertility from Atlantic salmon (Salmo salar L.) sperm frozen with four cryodiluents in straws or pellets

The cryopreservation of salmonid sperm is a complex process involving the interplay of many factors. Although cryopreservation protocols can be evaluated through a range of responses at various stages in the process, the number of progeny is the ultimate indicator of success. We compared reproductive success from freezing Atlantic salmon (Salmo salar L.) sperm using the eight combinations of (1) the penetrating cryoprotectants, 10% dimethyl sulfoxide (DMSO) or methanol (MeOH); (2) the nonpenetrating cryoprotectants glucose (0.3 M) or sucrose (0.6 M), and freezing in 0.1 mL pellets or 0.25 mL straws. All cryodiluents were supplemented with 10% (v/v) of hen's egg yolk. Response variables were the percentage and degree of motility of thawed and activated sperm using computer assisted sperm analysis (CASA), and rates of eyed embryos, hatch and egg sac larvae. Growth rates of alevins were assessed to two months post hatch. Atlantic salmon milt cryopreserved in straws had higher spermatozoa motility and fertilization success than milt cryopreserved in pellets (P < 0.05). Type of sugar tested did not significantly affect the response variables. In the MeOH treatment, thawed spermatozoa achieved higher speed and a higher fertilization rate evaluated at the eyed embryo stage than spermatozoa subjected to the DMSO treatment. Higher mortality rate (especially before hatching) of MeOH offspring than DMSO offspring led to equal numbers of progeny for the two treatments from the swimming stage to the end of the study. Moreover, during feeding fish from the MeOH group produced significantly lower weight larvae than the DMSO and control groups. Even so, the weight of the MeOH group was satisfactory. Length and the condition factors did not differ significantly among the larvae groups. Significant positive correlations were found between fertilization success (measured in number of eyed eggs) and both motility (rs = 0.81), and velocity (rs = 0.49). Freezing in straws gave betters results than freezing in pellets for cryopreservation of salmon milt; whereas type of sugar tested (glucose vs sucrose) did not have significant effects. Penetrating cryoprotectants DMSO and MeOH differed in their effect on post-thawed sperm velocity, fertilization rate and mortality rate of progeny, suggesting the need for further research on the influence of these cryoprotectants on frozen sperm and and post-fertilization devopmental processes.     

Comparison between PIT and radio telemetry to evaluate winter habitat use and activity patterns of juvenile Atlantic salmon and brown trout

Winter habitat use and activity patterns of juvenile Atlantic salmon and brown trout were analysed in a comparative study between Passive Integrated Transponder (PIT) technology, radio telemetry and underwater observation by snorkelling. Two study periods were conducted in Stoney River, Newfoundland, Canada. During Study period I, 49 juvenile Atlantic salmon (fork length: 11.0–18.0 cm) and 7 brown trout (11.0–17.3 cm) were tagged with PIT tags and/or radio transmitters in late winter of 2004. During Study period II, 18 juvenile Atlantic salmon (fork length: 12.0–18.4 cm) and 23 brown trout (10.9–20.8 cm) were tagged and tracked twice a day at 10:00 h and 22:00 h on five consecutive days in late winter of 2005. From the 56 fish released during Study period I, on average 19.6 ± 6.0% of the PIT tagged fish and 99.3 ± 2.2% of the radio tagged fish were relocated during any given survey. Over the Study period II, 39% of fish emigrated from the study site. PIT technology had an efficiency of 39.2 ± 14.1% to detect the remaining fish. In contrast, radio telemetry relocated on average 96.9 ± 6.5% of the tagged fish whereas by snorkelling on average only 4.1 ± 5.6% of the tagged fish were observed. PIT telemetry may however be more efficient in smaller, less heterogeneous streams. The advantage of PIT technology over radio telemetry is clearly that it is relatively less costly permitting higher numbers of individuals to be tagged and there is no limit in the operational life of the transponder. In winter, juvenile salmonids preferred low flow velocity and no preferences were observed for any specific water depth over the range of available water depths. Fish selected preferentially boulder habitat over other substrates in the environment. Habitat utilisation did not differ between day and night. The use of winter preference indices may be important for future habitat modelling.     

大西洋鲑杀鲑气单胞菌无色亚种的分离鉴定和致病性研究

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