Atlantic Salmon Eggs Research Articles

Some quantitative indicators of postovulatory aging and its effect on larval and juvenile development of Atlantic salmon (Salmo salar)

Modern out-of-season egg production in Atlantic salmon (Salmo salar) increases the risk of postovulatory aging (POA) of oocytes. Postovulatory aging is known to influence oocyte quality in salmonids, but reliable tests for POA are lacking in Atlantic salmon egg production. To address this problem, we have collected oocytes from the same 20 Atlantic salmon females sequentially in approximately 1-week intervals, from the start of ovulation until 28 days postovulation (dpo), to determine the effect of natural retention of matured oocytes in body coelomic cavity on further performance of embryos and juveniles produced from those oocytes. Also, we investigated oocyte water hardening and several coelomic fluid parameters as potential quantitative indicators of POA. Oocyte quality decreased significantly from 22 dpo onward, as inferred from decrease in fertilization success and survival of embryos, alevins, and juveniles and increase in alevin and juvenile deformity rates. The occurrence of head deformities was significantly related to postovulatory age of oocytes. Coelomic fluid pH decreased significantly at 28 dpo and correlated positively with fertilization rates (r = 0.45), normal eyed embryo rates (r = 0.67), and alevin relative survival rates (r = 0.63) and negatively correlated with total alevin deformity rates (r = −0.59). Oocyte weight gain at 60 minutes decreased significantly at 28 dpo and correlated negatively with total alevin deformities and the occurrence of cranial nodules (r = −0.99). Generally, quality of ovulated oocytes remained stable for the first 2 weeks after ovulation. Later on, POA negatively influenced Atlantic salmon embryo, alevin, and juvenile performance. For the first time, we show a long-term effect of POA on salmonid juvenile performance. Standardized pH measurements of coelomic fluid could potentially improve embryo and juvenile production by identifying low-quality oocytes at an early stage during the production.

The Impact of Egg Ozonation on Hatching Success, Larval Growth, and Survival of Atlantic Cod, Atlantic Salmon, and Rainbow Trout.

The direct exposure of fish eggs to ozonated water has generated interest as a means of ensuring pathogen-free eggs without the use of harsh chemicals. However, there are numerous knowledge gaps, including safe contact times, exposure levels, and potential long-term effects on aquaculture species in both freshwater and seawater. The effect of different ozone (O3) doses (0.5-1.0, 1.5-2.0, and 2.5-3.0 mg of O3/L for 90 s) on recently fertilized eggs of Atlantic Cod Gadus morhua and eyed eggs of Atlantic Salmon Salmo salar and Rainbow Trout Oncorhynchus mykiss was evaluated in comparison with the effects of two commercial disinfectants: Perosan (0.004 mg/L) and Ovadine (100 mg/L). The impact of ozone application was evaluated based on hatching success, larval nucleic acid concentration, larval growth, and survival. Overall, results indicated that ozonation of Atlantic Cod eggs at a dose less than 3.0 mg/L for 90 s produced no negative effect on the larvae up to 30 d posthatch. Furthermore, ozonation of Atlantic Salmon and Rainbow Trout eggs generated no negative effect on the larvae, based on monitoring until 85% yolk sac re-absorption (16 d posthatch).

AquAdvantage® Salmon - a pioneering application of biotechnology in aquaculture

The U.S. FDA is currently reviewing AquaBounty Technologies' New Animal Drug Application for a fast growing transgenic Atlantic salmon, known as AquAdvantage® Salmon, which would be the first genetically modified food animal approved for human consumption. AquAdvantage® Salmon was developed by inserting into a fertilized Atlantic salmon egg, a transgene constructed from the growth hormone gene of a related species (Chinook salmon). The AquAdvantage® genetic construct confers upon the Atlantic salmon a rapid growth phenotype and improved metabolic efficiencies associated with low but sustained levels of growth hormone. This allows the fast growing AquAdvantage® Salmon to reach market size in half the time of a conventional Atlantic salmon. AquAdvantage® Salmon will be available only as all female, sterile, eyed eggs, and the resulting fish must be maintained in a freshwater, land based, physically contained facility [1]. The founding line of AquAdvantage® Salmon was created in 1989, and an Investigational New Animal Drug (INAD) dossier was opened with the FDA in 1995. In 2009, AquaBounty submitted to the FDA the last of more than 25 scientific studies in support of our application. In 2010 the FDA presented their findings to the Veterinary Medical Advisory Committee (VMAC), and recommended an approval. The VMAC committee, comprised of independent experts selected from academia, industry, and NGO's, concurred with the FDA's findings, which were that AquAdvantage® Salmon is equivalent to conventional farmed Atlantic salmon, and is safe for human consumption as well as safe for the environment. The regulatory analysis included an environmental assessment of a proposed AquAdvantage® Salmon egg production site in Canada, and an AquAdvantage® Salmon growout site in Panama, both of which were inspected and approved by the FDA. Important biosecurity elements for containing AquAdvantage® Salmon and minimizing potential risk to the environment at the two production sites include physical, biological, and environmental containment. For example, at the proposed growout site in Panama which is more than 120 km from the nearest ocean, sterile, all female populations of AquAdvantage® Salmon are confined to a highly biosecure culture facility possessing 21 individual containment elements, with a minimum of eleven containment barriers in sequence. In addition to the biological and physical containment elements, a natural thermal barrier of lethally high water temperatures (for Atlantic salmon) downstream of the facility would effectively prevent any live, escaped AquAdvantage® Salmon from reaching the Pacific Ocean. In 2012 the FDA published the environmental assessment for public commentary, and a Finding of No Significant Impact (FONSI), indicating that rearing AquAdvantage® Salmon in those sites did not present a risk to the environment when reared under the conditions of use stipulated by the FDA. The public comment period concluded in April of 2013, and a final resolution of the application is expected this year from the FDA. If approved by the FDA, the product offered by AquaBounty would be eyed eggs of AquAdvantage® Salmon, which would carry an FDA approved label indicating that they are female, triploid, genetically engineered Atlantic salmon eggs carrying a single copy of the AquAdvantage®gene construct. The label would also stipulate that the fish from these eggs could only be grown in pre-approved, land based, physically contained, freshwater aquaculture facilities. As a pioneering application for a genetically modified animal destined for human consumption, AquAdvantage® Salmon has attracted considerable attention and opposition by anti-GMO, anti-biotech activist organizations, as well as the organic food industry which is threatened by the more productive, lower cost, food production alternatives offered by GM plant and animal biotechnology. Resigned to accepting the inevitable regulatory approval of GM salmon and other innovative animal biotech products, the anti-GMO community is now desperately resorting to labeling initiatives, and economic extortion of future market stakeholders, in an effort to commercially stigmatize genetically modified food products.

Survival of eggs of Atlantic salmon (Salmo salar) in a drawdown zone of a regulated river influenced by groundwater

Groundwater may create refuges for Atlantic salmon egg survival during low flows in regulated rivers and thus play an important role for survival during winter. To investigate the links between the survival of salmon embryos and hyporheic hydrological processes during permanent winter drawdown, a 100-m-long and 50-m-wide gravel area in a regulated river, the River Suldalslagen, was used for an experimental study. Surface and subsurface water levels were monitored with 2-min time resolution by means of water pressure sensors placed in pipes. Temperature, conductivity and dissolved oxygen were also measured. Eight cylindrical boxes, each with two compartments (at 10- and 30-cm depth, respectively) containing 50 Atlantic salmon eggs, were placed in the river bed substrate of both the drawdown zone and the permanently wetted area as a reference. They were regularly checked for survival during winter from January to May, coinciding with egg development period for this river. Survival rates in boxes in the dewatered river bed were between 8 and 78% during winter, compared to 80 to 99% in the reference wetted area. The main driver for egg survival in the dewatered area was groundwater with sufficient oxygen levels.

The Survival of Atlantic Salmon (Salmo salar) Eggs During Dewatering in a River Subjected to Hydropeaking

AbstractHydropeaking in regulated rivers is likely to become more frequent with increasing demands for renewable energy. Sudden fluctuations affect surface and subsurface flow regimes and change hydrological interactions occurring in the hyporheic zone. The hyporheic zone plays an important role for salmon embryonic development, and groundwater influx may create refuges for egg survival during low flow in hydropeaking regulated rivers. The links between salmon embryo survival and hyporheic hydrological processes during hydropeaking have hardly been investigated.A field experiment was undertaken in a 5 × 20 m side gravel bar subject to dewatering due to hydropeaking. Eleven cylindrical boxes composed of eight compartments were placed in the permanently wet area and the ramping zone. Sixty eggs were placed in two compartments (at 10 and 30 cm depth) in each box. Surface and interstitial water levels and temperatures were monitored at 2 min resolution. Data were collected for a period of 3 months, coinciding with early stages of salmonid egg development in this catchment. Egg compartments were checked on six occasions for survival after different hydropeaking events. Dead eggs were counted and removed. Survival rates were lower in the top compartments in the ramping zone (78%) compared with the boxes in the permanently wet area and the lowermost compartments in the ramping (survival rates >99%). With no water quality issues in the catchment and very low inputs of fine sediments in the egg compartments, exposure to dry conditions and subzero temperatures were the main factors explaining egg mortality in the top compartments of the ramping zone. The rate of survival will thus depend on the surface water and groundwater interactions. Site‐specific hydrological interactions occurring in the hyporheic zone should be actively considered when managing fish populations in rivers with hydropeaking. Copyright © 2014 John Wiley & Sons, Ltd.

Signal crayfish (Pacifastacus leniusculus) predation upon Atlantic salmon (Salmo salar) eggs

Abstract The signal crayfish (Pacifastacus leniusculus) is a large, polytrophic crustacean which has invaded waterways across much of Europe. Crayfish prey on the eggs of several fish species and egg predation, especially by invasive crayfish, is cited as a likely cause of population decline and a serious concern for the conservation of some fish species including at least one salmonid. Numerically, crayfish populations may be dominated by small individuals, but most studies have investigated egg predation by large crayfish. Evidence for crayfish gaining access to buried fish eggs is equivocal. The ability of signal crayfish of a range of age groups (and hence, sizes) to prey on unburied and buried Atlantic salmon (Salmo salar) eggs was investigated in laboratory experiments. Only Age 2+ and older crayfish (24–43 mm carapace length (CL)) significantly reduced egg survival in unburied egg experiments, although some evidence of egg predation was observed with Age 1+ crayfish (16–22 mm CL). Age 0+ crayfish (8–14 mm CL) did not prey on salmon eggs. No evidence of substantial excavations or predation upon buried eggs by crayfish of any size class was observed. Binomial logistic regression of egg survival against crayfish CL indicated that mean egg recovery fell below control levels when CL exceeded 16.3 mm. These results suggest that large signal crayfish are likely to pose the greatest threat to salmonid eggs, but that crayfish larger than 16.3 mm CL have the potential to prey on eggs. Further research is needed before manual removal or harvesting of signal crayfish are used as conservation measures for Atlantic salmon spawning areas in which signal crayfish occur. Restoration of high‐quality salmonid spawning habitat might, however, help to prevent signal crayfish predation of salmonid eggs in addition to broader benefits for salmonid conservation. © 2014 Crown copyright. Aquatic Conservation: Marine and Freshwater Ecosystems © 2014 John Wiley & Sons, Ltd.

Reprint of: Saprolegnia strains isolated from river insects and amphipods are broad spectrum pathogens

Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. Reports based on phylogenetic analysis suggest that Saprolegnia strains isolated from aquatic animals such as crustaceans and frogs are close to Saprolegnia strains isolated from infected fish or fish eggs and vice versa. However, it has often been assumed that host specificity occurs for each individual isolate or strain. Here we demonstrate that Saprolegnia spp. can have multiple hosts and are thus capable of infecting different aquatic organisms. Saprolegnia delica, Saprolegnia hypogyna, and 2 strains of Saprolegnia diclina were isolated from aquatic insects and amphipods while S. delica, Saprolegnia ferax, Pythium pachycaule, and a Pythium sp. were isolated from the water of a medium to fast flowing river. The ITS region of the rRNA gene was sequenced for all isolates. In challenge experiments, all four isolates from insects were found to be highly pathogenic to eggs of Atlantic salmon (Salmo salar) and embryos of the African clawed frog (Xenopus laevis). We found that Saprolegnia spp. isolated from salmon eggs were also able to successfully establish infection in nymphs of stonefly (Perla bipunctata) and embryos of X. laevis). These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments.

Deciphering microbial landscapes of fish eggs to mitigate emerging diseases.

Animals and plants are increasingly suffering from diseases caused by fungi and oomycetes. These emerging pathogens are now recognized as a global threat to biodiversity and food security. Among oomycetes, Saprolegnia species cause significant declines in fish and amphibian populations. Fish eggs have an immature adaptive immune system and depend on nonspecific innate defences to ward off pathogens. Here, meta-taxonomic analyses revealed that Atlantic salmon eggs are home to diverse fungal, oomycete and bacterial communities. Although virulent Saprolegnia isolates were found in all salmon egg samples, a low incidence of Saprolegniosis was strongly correlated with a high richness and abundance of specific commensal Actinobacteria, with the genus Frondihabitans (Microbacteriaceae) effectively inhibiting attachment of Saprolegniato salmon eggs. These results highlight that fundamental insights into microbial landscapes of fish eggs may provide new sustainable means to mitigate emerging diseases.

Size and ATP Content of Unfertilized Eggs from Farmed and Wild Atlantic Salmon in Newfoundland

AbstractIn Newfoundland and Labrador (hereafter, Newfoundland), all farmed Atlantic Salmon Salmo salar originate from the Saint John River, New Brunswick, strain, raising the question of potential impacts of escapees on wild, genetically distinct stocks. Unfertilized eggs of farmed and wild salmon were assessed for diameter, mass, adenosine triphosphate (ATP) content, and fertilization success, this is the first study to assess ATP content in Atlantic Salmon eggs. Results demonstrated that farmed salmon egg mass (0.1046 g), diameter (6.2 mm), and ATP content (0.0281 nmol/egg) were significantly lower than the same characteristics in wild salmon. Among and within females, variability in egg size was similar in both wild and farmed groups. This study lends some evidence to the fact that in the Newfoundland context, eggs of escaped farmed salmon may be less likely to produce viable, large larvae compared with their wild counterparts.Received September 17, 2013; accepted December 6, 2013

Assessing risks of invasion through gamete performance: farm Atlantic salmon sperm and eggs show equivalence in function, fertility, compatibility and competitiveness to wild Atlantic salmon.

Adaptations at the gamete level (a) evolve quickly, (b) appear sensitive to inbreeding and outbreeding and (c) have important influences on potential to reproduce. We apply this understanding to problems posed by escaped farm salmon and measure their potential to reproduce in the wild. Farm Atlantic salmon (Salmo salar) are a threat to biodiversity, because they escape in large numbers and can introgress, dilute or disrupt locally adapted wild gene pools. Experiments at the whole fish level have found farm reproductive potential to be significant, but inferior compared to wild adults, especially for males. Here, we assess reproductive performance at the gamete level through detailed in vitro comparisons of the form, function, fertility, compatibility and competitiveness of farm versus wild Atlantic salmon sperm and eggs, in conditions mimicking the natural gametic microenvironment, using fish raised under similar environmental conditions. Despite selective domestication and reduced genetic diversity, we find functional equivalence in all farm fish gamete traits compared with their wild ancestral strain. Our results identify a clear threat of farm salmon reproduction with wild fish and therefore encourage further consideration of using triploid farm strains with optimized traits for aquaculture and fish welfare, as triploid fish remain reproductively sterile following escape.

Saprolegnia strains isolated from river insects and amphipods are broad spectrum pathogens

Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. Reports based on phylogenetic analysis suggest that Saprolegnia strains isolated from aquatic animals such as crustaceans and frogs are close to Saprolegnia strains isolated from infected fish or fish eggs and vice versa. However, it has often been assumed that host specificity occurs for each individual isolate or strain. Here we demonstrate that Saprolegnia spp. can have multiple hosts and are thus capable of infecting different aquatic organisms. Saprolegnia delica, Saprolegnia hypogyna, and 2 strains of Saprolegnia diclina were isolated from aquatic insects and amphipods while S. delica, Saprolegnia ferax, Pythium pachycaule, and a Pythium sp. were isolated from the water of a medium to fast flowing river. The ITS region of the rRNA gene was sequenced for all isolates. In challenge experiments, all four isolates from insects were found to be highly pathogenic to eggs of Atlantic salmon (Salmo salar) and embryos of the African clawed frog (Xenopus laevis). We found that Saprolegnia spp. isolated from salmon eggs were also able to successfully establish infection in nymphs of stonefly (Perla bipunctata) and embryos of X. laevis). These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments.

Use of Stable Isotopes to Identify Redds of Putative Hatchery and Wild Atlantic Salmon and Evaluate Their Spawning Habitat and Egg Thiamine Status in a Lake Ontario Tributary

AbstractBoth wild and hatchery Atlantic Salmon Salmo salar can contribute to restoration but can exhibit differences in spawning habitat selection (e.g., water depth, current speed) and egg nutritional quality (e.g., thiamine), which affect reproductive success. Hence, there is a need to be able to differentiate the spawning contribution of the two groups in the wild. As diets of wild and hatchery‐reared spawners are markedly dissimilar and diet is known to influence stable isotope signature, egg stable isotope signatures offer the potential to discriminate redds of each. Using stable isotope analysis of carbon and nitrogen (δ13C and δ 15N) of naturally spawned Atlantic Salmon eggs, we were able to discriminate the redds of putative wild (i.e., previously stocked life stage feeding in Lake Ontario; EWSR) from putative hatchery‐reared Atlantic Salmon (EHSR). Eggs of EWSR were significantly more enriched in nitrogen (δ15N: 15.0 ± 0.5‰ [mean ± SE]) but more depleted in carbon (δ13C: −26.6 ± 0.3‰) than eggs of EHSR (δ15N = 9.8 ± 0.6‰; δ13C = −17.5 ± 0.0‰). Eggs of EHSR were indistinguishable from eggs of known hatchery Atlantic Salmon for both δ13C and δ 15N. Using stable isotopes to discriminate redd type, few differences were found between the spawning habitat of putative wild and hatchery spawners. Similarly using the same criteria, thiamine levels in eggs of EWSR (8,474 ± 840 pmol/g) were not significantly different from eggs of known wild Atlantic Salmon (3,691 ± 782 pmol/g) or of eggs of EHSR (14,865 ± 1,050 pmol/g), whose thiamine levels were indistinguishable from eggs of known hatchery Atlantic Salmon (14,200 ± 1,167 pmol/g). Egg thiamine levels for all groups were above established mortality thresholds. Our results indicate that both hatchery and wild Atlantic Salmon can make reproductive contributions, which can be differentiated and quantified using stable isotope signatures.Received August 24, 2012; accepted May 15, 2013

Incubation, hatching and survival of eggs of Atlantic salmon (Salmo salar) in spawning redds influenced by groundwater

Many west coastal and northern Norwegian rivers run through deep, confined valleys with permeable layers of glacial and alluvial deposits. Groundwater flows through these permeable layers and enter lakes and rivers as underwater seepage and springs. Groundwater inflow to inland Norwegian rivers may constitute 40–100% of total water discharge during low flow periods in late summer and winter. Juvenile salmonids may take advantage of groundwater upwellings and actively seek out such patches. In regulated rivers groundwater influx may create refuges during low flow or hydropeaking episodes. The importance of groundwater for salmon redd site selection and egg survival is also clear, although less known and documented in regulated rivers. Eggs of Atlantic salmon ( Salmo salar ) are deposited in redds in river bed gravels lacking fine sediments and with high oxygen levels. Egg development is therefore dependent on the interaction of a number of environmental factors such as groundwater influx, oxygen and temperature. Atlantic salmon in the regulated River Suldalslågen, Western Norway, spawn relatively late compared to other Norwegian rivers, with a peak in early January. Newly emerged fry are found from the end of May to the beginning of June, i.e. “swim up” one month earlier than expected using models for egg and alevin development and river water temperatures. The most plausible explanation is that groundwater has a higher and more stable temperature than surface river water. In field experiments, fertilized salmon eggs were placed in boxes close to natural spawning redds in the river bed at sites influenced and those not influenced by groundwater. A difference of up to 40 days in 50% hatching was found, and “swim up” occurred at the end of May in boxes influenced by groundwater. Preliminary studies have revealed that groundwater also plays an important role in survival of salmon eggs in the River Suldalslågen when dewatered in winter. Eggs placed in boxes in groundwater seepage areas during winter in the dewatered river bed survived even when covered by ice and snow. The survival from fertilization until 30 April, one month before hatching, was 91%, the same survival as found for eggs placed in boxes in the wetted river bed. However, mortality from fertilization to hatching was higher compared to the eggs placed in wetted river bed, 57 and 91% respectively. Groundwater creates a horizontal and vertical mosaic of temperatures in spawning redd areas leading to potentially greater variation in spawning sites, time of hatching and “swim up”. This is likely to increase egg survival during low flow periods in regulated rivers. In conclusion, the interaction between groundwater and surface river water should therefore be considered when managing fish populations in regulated rivers.

Screening of macro- and bioactive microconstituents of commercial finfish and sea urchin eggs

Crude and lipid composition, tocopherols, carotenoids, sterols and squalene content, together with fatty acids profiles of commercial marine egg products are reported, namely (a) canned eggs of lumpfish (Cyclopteris lumpus), Atlantic salmon (Salmo salar), trout (Oncorhynchus mykiss), smoked herring (Clupea harengus), and sea urchin (Paracentrotus lividus), (b) fresh sea urchin (P. lividus) eggs, and (c) beeswax covered, dried and salted mullet (Mugil cephalus) skeins -Greek “Avgotaracho”. The protein content of marine eggs ranged from 8.7 to 33.7 g/100 g on a fresh weight (fw) basis. Among neutral lipids triacylglycerols predominated, except for mullet roe where wax and steryl esters comprised 75% of neutral lipids. Phosphatidylcholine was the major phospholipid, followed by phosphatidylethanolamine. Marine eggs contained 0.18–2.39 g/100 g fw long chain ω3 polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid (DHA) in finfish eggs and eicosapentaenoic acid (EPA) in urchin eggs. They also contained 86.2–342.0 mg cholesterol/100 g fw, low amounts of squalene and other sterols and significant amounts of tocopherols (0.45–4.4 mg/100 g) and carotenoids (0.31–11.4 mg/100 g). The commercial finfish and urchin eggs are food of high nutritive value providing significant amounts of protein, ω3 PUFA, phosphatidylcholine, carotenoids, and tocopherols, with fatty acids profiles that exhibit low atherogenic and thrombogenic potential.

Investigating the threat of non-native North American signal crayfish (Pacifastacus leniusculus) to salmon redds

To test their ability to detect and excavate Atlantic salmon eggs (Salmo salar) in an artificial redd, North American signal crayfish (Pacifastacus leniusculus) were exposed to three successive experimental treatments. Crayfish successfully detected and excavated buried fish but were unable to detect buried salmon eggs, despite significant opportunity. The results strongly suggest that signal crayfish do not present a threat to Atlantic salmon via egg predation. In the wild, however, the vulnerability of redds may vary according to a range of biotic and abiotic factors. Copyright © 2011 John Wiley & Sons, Ltd.

REMOVAL OF WEIRS AND THE INFLUENCE ON PHYSICAL HABITAT FOR SALMONIDS IN A NORWEGIAN RIVER

ABSTRACTIn the late 1970s, the construction of weirs in Norwegian regulated river systems for aesthetic reasons was common. However, today, the focus of river restoration has shifted towards improving biological functionality and biodiversity. In the present study, two weirs, originally built to create a stable water level, were removed on a residual flow reach in a Norwegian regulated river as a measure to restore river connectivity and to re‐establish the local population of Atlantic salmon. The removal design was based on hydraulic modelling, and biological monitoring was implemented before and after the weir removal to evaluate the biological response to weir removal. The results demonstrated that salmon spawning sites were recreated in the old bed substratum and were occupied immediately the first season after weir removal, when water velocities increased to more suitable levels for spawning. Accordingly, mortality of Atlantic salmon eggs was reduced and the densities of juveniles showed a marked increase after weir removal. Conversely, pike and cyprinids in the reach were found in the samples before weir removal but not after removal, indicating that the desired shift in fish community in response to habitat alteration was obtained. Furthermore, enumeration of migrating adult salmon at a fishway upstream of the study reach showed that the migration peak, on average, was 1 month earlier in the 3 years after removal as compared with the 5 years before removal. Finally, the use of hydraulic modelling represented a useful method for designing physical habitat adjustments and assessing their influence on fish biology. The model results also supported a rapid process in planning and execution of construction works. Copyright © 2011 John Wiley & Sons, Ltd.

Efficacy and Toxicity of Iodine Disinfection of Atlantic Salmon Eggs

AbstractRecent interest in the restoration of Atlantic salmon Salmo salar in the Great Lakes has given rise to new culture techniques and management programs designed to reduce pathogen transmission while stabilizing and enhancing wild populations. We examined the toxicity of iodine to Atlantic salmon eggs and its effectiveness as a disinfectant against bacteria on egg surfaces. We spawned and fertilized eight gravid Atlantic salmon from Cayuga Lake, New York, and exposed their eggs to 10 concentrations of iodine (5, 10, 50, 75, 100, 500, 750, 1,000, 5,000, and 7,500 mg/L) for 30 min during water hardening. An additional subsample of unfertilized eggs was also exposed to some of the same concentrations of iodine (5, 10, 50, 75, and 100 mg/L) to determine the efficiency of disinfection. Viable eggs were only obtained from four females. Survival of eggs to the eyed stage and hatch tended to be reduced at iodine concentrations of 50 and 75 mg/L and was significantly reduced at concentrations of 100 mg/L iodine or more. We calculated the concentrations of iodine that killed 50% of the Atlantic salmon eggs at eye‐up and hatch to be 175 and 85 mg/L, respectively. Aeromonas veronii, A. schubertii, A. hydrophila, A. caviae, Plesiomonas shiggeloides, and Citrobacter spp. were the predominant bacteria present on the surface of green eggs and were significantly reduced by an iodine immersion. The use of iodine as a disinfectant on Atlantic salmon eggs was effective at low concentrations (50–75 mg/L), for which toxicity to Atlantic salmon was minimal.Received June 8, 2010; accepted September 19, 2010

Atlantic salmon eggs favour sperm in competition that have similar major histocompatibility alleles.

Polyandry and post-copulatory sexual selection provide opportunities for the evolution of female differential sperm selection. Here, we examined the influence of variation in major histocompatibility (MH) class I allelic composition upon sperm competition dynamics in Atlantic salmon. We ran in vitro fertilization competitions that mimicked the gametic microenvironment, and replicated a paired-male experimental design that allowed us to compare differences in sperm competition success among males when their sperm compete for eggs from females that were genetically either similar or dissimilar at the MH class I locus. Concurrently, we measured variation in spermatozoal traits that are known to influence relative fertilization success under these conditions. Contrary to the findings demonstrating mechanisms that promote MH complex heterozygosity, our results showed that males won significantly greater relative fertilization success when competing for eggs from genetically similar females at the MH class I. This result also showed covariation with the known influences of sperm velocity on relative fertilization success. We discuss these unexpected findings in relation to sperm–egg recognition and hybridization avoidance mechanisms based upon immunogenetic variation.

Strong genetic influence on IPN vaccination‐and‐challenge trials in Atlantic salmon, Salmo salar L.

Two series of experimental challenge trials were performed for evaluation of multivalent oil-adjuvanted vaccines with and without an infectious pancreatic necrosis virus (IPNV) antigen component. In both the trial series, Atlantic salmon were hatched, reared, vaccinated and subjected to temperature and light manipulation to induce smoltification. When ready for sea the fish were transported to the VESO Vikan experimental laboratory for bath or cohabitant challenge with IPNV. In the first series, four vaccination and bath challenge trials involving 2-year classes of experimental fish were conducted. In the second series, three groups of eyed eggs of Atlantic salmon allegedly differing in their innate resistance to IPNV were used (Storset, Strand, Wetten, Kjøglum & Ramstad 2007). Hatching, rearing and smoltification were synchronized for each group, and fish from each genetic group were randomly allocated IPN vaccine, reference vaccine or saline before being placed into parallel tanks for bath or cohabitant challenge. In the first series of trials, IPN-specific mortality commenced on day 10-12 after bath challenge. Replicates showed similar results. In trials 1 and 2 belonging to the same experimental fish year class, the average cumulative control mortality reached 60.6% and 79.5%, respectively, whereas in trials 3 and 4 belonging to the following year class the control mortality was consistently below 50%. In the second series of trials, the experimental fish originating from allegedly IPN susceptible parents consistently showed the highest cumulative mortality among the unvaccinated controls (>75%) whereas smolts derived from allegedly IPNV resistant parents showed only 26-35% control mortality. The IPN-vaccinated fish experienced significantly improved survival vs. the fish immunized with reference vaccine, with RPS values above 75% in the IPN susceptible strain. In the IPN resistant strain, the protection outcomes were variable and in part non-significant. The outcome of both the trial series suggests that control mortalities above 50% are necessary to reliably demonstrate specific protection with IPN vaccines.

Nest distribution shaping within‐stream variation in Atlantic salmon juvenile abundance and competition over small spatial scales

1. Spatial heterogeneity in population density is predicted to have important effects on population characteristics, such as competition intensity and carrying capacity. Patchy breeding distributions will tend to increase spatial heterogeneity in population density, whereas dispersal from breeding patches will tend to decrease it. The potential for dispersal to homogenize densities is likely to differ both among organisms (e.g. plants vs. mobile animals) and throughout ontogeny (e.g. larvae vs. adults). However, for mobile organisms, experimental studies of the importance of breeding distributions from the wild are largely lacking. 2. In the present study, experimental manipulations replicated over eight natural streams and 2 years enabled us to test for effects of the distribution of Atlantic salmon eggs over spatial scales which are relevant to local interactions among individuals. Artificial nests were placed along 250 m study reaches at one of two levels of nest dispersion - patchy (two nests per stream) and dispersed (10 nests per stream) - while holding total egg density (eggs m(-2) stream area) constant. 3. Nest dispersion had significant effects on the spatial distribution of the resulting juveniles in their first summer. Patchy nest distributions resulted in a highly right-skewed frequency distribution of local under-yearling densities (among 25 m sampling sections), as sample sections adjacent to the nest sites had relatively high densities. In contrast, dispersed nest distributions yielded approximately normal density distributions. Sections with high relative densities in the patchy nest distribution treatments also had relatively small juvenile body sizes, and patchy egg distribution appeared to produce a higher redistribution of individuals from the first to the second juvenile growth season than the dispersed distribution. 4. Because patchy breeding distribution combined with limited early dispersal can create spatial variation in density over scales directly relevant for individual interactions, this will be one important component in determining mean levels of early juvenile competition and its spatial variation within populations. Assuming random or ideal-free distribution of individuals may therefore underestimate the mean level of density experienced by juveniles over surprisingly small spatial scales (orders of magnitude smaller than total spatial extent of populations), even for mobile organisms.