Environmental and Genetic (vgll3) Effects on the Prevalence of Male Maturation Phenotypes in Domesticated Atlantic Salmon

Pre-harvest male maturation is problematic for Atlantic salmon (Salmo salar) farmers and is regulated by the environment and genetics (e.g., vgll3). Five families of all-male salmon parr (produced using YY males crossed with XX females) with different vgll3 genotypes were split between three environmental regimes in January 2018. The “advanced maturation” regime used elevated temperature (16 °C) and continuous light from January 2018 with post-smolt maturation assessed in March 2018. The “extended freshwater” regime used ambient freshwater (1–16 °C) and simulated natural photoperiod (SNP) with post-smolt maturation assessed in November 2018. The “sea transfer” regime used ambient temperatures (1–14 °C) and SNP in freshwater until May 2018 when they were transferred to 9 °C seawater with natural photoperiod for 2.5 years (final mean weight of circa. 14 kg) and assessed for post-smolt maturation, 1 sea-winter (1 SW) maturation, and 2 sea-winter (2 SW) maturation in the autumn (November/December) of 2018, 2019, and 2020, respectively. Post-smolt maturation was highest in the advanced maturation and extended freshwater regimes (39–99% depending on family) and lowest in the sea transfer regime (0–95% depending on family). In the sea transfer regime, maturity incidence increased over time (0–95% post-smolt maturation, 1–100% 1 SW, and 50–90% 2 SW maturation, depending on family). In all regimes, those homozygous for the pre-designated vgll3 “early” maturing allele had the highest incidences of maturation whilst those homozygous for the “late” allele had the lowest. A low percentage of 2 SW phenotypic and genetic females were found (0–5% depending on family), one of which was successfully crossed with an XY male resulting in progeny with an approx. 50/50 sex ratio. These results show (i) post-smolt maturation varies dramatically depending on environment although genetic regulation by vgll3 was as expected, and (ii) crossing YY sperm with XX eggs can result in XX progeny which can themselves produce viable progeny with an equal sex ratio when crossed with an XY male.publishedVersio

Effects of laboratory salmon louse infection on osmoregulation, growth and survival in Atlantic salmon

Anadromous Atlantic salmon (Salmo salar) rely on long ocean migrations to build energy stores for maturation and spawning. In seawater, wild Atlantic salmon are threatened by high salmon lice (Lepeophtheirus salmonis) infestation levels resulting from intensive salmonid sea-cage aquaculture. Salmon lice infection can cause a stress response and an osmotic imbalance in the host. The lice infection intensity threshold values for these responses, however, remain to be identified in Atlantic salmon. In order to define this under laboratory conditions, individually tagged F1 wild origin Atlantic post-smolts (40 g) were infected with salmon lice copepodids or left as uninfected controls. Twenty-eight days post infection, infected post-smolts had a mean of 0.38 (range of 0.07–0.9) mobile lice g−1 fish weight. During this period, specific growth rates (SGRs) were lower in infected than control fish (0.4 vs 1.0% day−1). Higher plasma Na+, Cl− and osmolality in infected fish also indicate osmoregulatory impairment. SGR correlated negatively with plasma Na+, Cl−, osmolality and cortisol in the infected, but not in the control group. Infection intensity (lice g−1 fish) correlated positively with mortality rate and plasma Na+, Cl−, osmolality and cortisol and correlated negatively with SGR and condition factor. Calculated lice intensity threshold values for changes in plasma ions were 0.18 lice g−1 for plasma Cl−, and 0.22 lice g−1 for plasma Na+. Moribund infected fish occurred at infection intensities above 0.2 lice g−1, and these fish had extreme plasma Cl−, Na+, osmolality and cortisol levels. There was a positive correlation between plasma cortisol and plasma Na+, Cl− and osmolality in infected fish. This study provides vital information that can be used to define thresholds in the monitoring and conservation of wild Atlantic salmon populations affected by aquaculture-driven salmon lice infestations.publishedVersio

Vertebral deformities in interspecific diploid and triploid salmonid hybrids

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Triploidy effects growth, life history strategies, and bone health in Arctic char (Salvelinus alpinus), but does not impact cataract incidence

Skeletal deformities and ocular cataracts have limited the farm performance of sterile triploid salmonids, but have not been assessed in Arctic char (Salvelinus alpinus). We repeatedly radiographed mixed-sex diploid and triploid char (n = 110/ploidy) of Hammerfest (Norway) origin reared on a natural photoperiod and temperature in freshwater over a 3-year period and assessed cataracts at termination. At the population level, triploids were significantly (p 90% in both ploidy), but severity was low (on average, 0.1). Based on the average wet body mass of immature fish and losses due to sexual maturation and mortality, mono-sex stocks of male triploid fish gave the highest return per 100 juveniles stocked, followed by diploid males, diploid females, and triploid females (87.5, 83.0, 80.8, and 69.3 kg, respectively) at the earliest opportunity to harvest (i.e. when the fish first reached 0.7–1.0 kg). Therefore, all-male triploids may provide benefits to char aquaculture although their skeletal health should be addressed.publishedVersio

Effects of light source and intensity on sexual maturation, growth and swimming behaviour of Atlantic salmon in sea cages

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Detecting and tracing farmed salmon with natural geo-element otolith ‘fingerprint’ tags: developing and validating tag delivery techniques

Farmed fish escape and enter the environment with possible effects on wild populations. Attempts to reduce the incidence of escape could be assisted if individuals can be traced back to the point of escape, so that escape causes can be identified and technical standards improved. We tested if permanent marks could be created on the otoliths of salmon that could be detected throughout the lives of the fish. Marks were created by altering the natural ratios of the natural elements barium (Ba) and strontium (Sr) in the otolith. By combining several natural geo-elements, unique fingerprints can be created, which can act as codes that enable tracing of fish back to the point of escape. The marks are detected by laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). We delivered marks to salmon in 4 different ways: 1) injecting female broodstock with geo-element markers prior to spawning so that the marks can be passed from the mother to all eggs in a clutch, with all larvae receiving a mark in the core of their otolith; 2) incorporating small amounts of geo-element markers into the vaccination serum for co-delivery of the marks into the fish along with the vaccine; 3) bathing eggs of salmon in geo-element solution immediately after fertilisation; and 4) bathing late stage yolk-sac larvae in an geo-element solution. All methods were successful in creating unique, permanent marks on the otoliths of salmon that could be detected throughout the lifetime of the fish. For all four delivery techniques, marking was 100% successful with Ba at concentrations as low as 0.001 μg. g-1 fish and for Sr at 1 μg. g-1 fish. Detection limits with the laser were set at 99.94%, so the techniques delivered a very high degree of accuracy. In all methods, we developed procedures that minimized marking and analysis costs, so that methods could be implemented at full-scale commercial application. After marking, fish were ongrown under standard commercial conditions to harvest size (approx. 4 kg). Marking methods had no effect on all standard production parameters, such as survival, growth, and the incidence of larval deformities compared to unmarked control fish. Further, the amounts of natural 2 strontium and barium used to create the marks are so small that they pose no problem for food safety, as they represent less than 0.1–1% of the amounts that naturally occur in salmon tissues. Our results indicate single marking with one of the techniques can create up to 63 unique fingerprint marks at low cost using Ba (0.0002–0.02 $US per mark) and Sr (0.46–0.82$US per mark). Double marking in different parts of the otolith using two of the different code delivery methods was also successful (e.g. maternal transfer and vaccination combined). This means 63 x 15 unique codes, or 1023 codes are possible, which is sufficient to provide a unique code for every site in the sea in Norway. We conclude that fingerprinting with natural geo-elements is feasible for commercial application. 94% of the salmon in Norway could be marked for as little as 0.02 $US per fish with a single marking method with traceability back to the top 63 producing companies. Double marking would enable more detailed tracing of every fish back to its site in the sea.Oppdrettslaks rømmer og kan påvirke de ville populasjonene. Antallet rømminger kunne vært redusert hvis den rømte fisken kunne vært sporet tilbake til rømningsstedet slik at årsaken til rømning kunne blitt identifisert. Vi testet om det er mulig å lage kjemiske merker på laksens ørestein som kan identifiseres gjennom hele livssyklusen. Disse merkene ble laget ved å endre forholdet mellom naturlige geoelementer (stabile isotoper av barium (Ba) og strontium (Sr)) i øresteinen. Ved å kombinere flere av disse naturlige geoelementene kan en lage unike ’fingeravtrykk/strekkoder’ som kan brukes for å spore en fisk tilbake til rømningsstedet. Merkene leses ved en teknikk hvor en brenner hull i øresteinen med laser og måler sammensetningen ved hjelp av massespektrometri. Merkene i øresteinen ble etablert ved hjelp av fire metoder: 1) ved å injisere morfisken med geoelementer i forkant av gytingen slik at disse kan overføres til alle eggene og at merket blir avsatt i øresteinens kjerne; 2) ved å tilsette små mengder av geoelementene i fiskens vaksine slik at fisken merkes ved vaksineringen; 3) ved å tilsette geoelementer i svellevannet som tilsettes rett etter befruktningen av eggene; 4) ved å bade plommesekkyngelen i en løsning med geoelementer. Ved alle metodene klarte vi å lage unike, permanente merker i øresteinen som kunne finnes og kjennes igjen gjennom hele fiskens livssyklus. Alle metodene ga 100 Etter merking ble fisken oppdrettet under standard oppdrettsbetingelser til slaktestørrelse (ca. 4 kg). Merkemetodene påvirket ingen produksjonsparametre som overlevelse, vekst eller innslag av deformiteter. Mengden naturlig strontium og barium som ble brukt er mindre enn 1 Våre resultater viser at en ved enkel merking med en av teknikkene kan lage opptil 63 unike ‘fingeravtrykk’ til en lav kostnad ved bruk av Ba (0,0002–0,02$US per merke) og Sr (0,46–0,82 $US per 3 merke). Dobbelmerking; dvs. å merke i ulike deler av øresteinen ved hjelp av to av metodene, var også mulig (for eksempel injeksjon av morfisk og vaksinering på parrstadiet). Dette betyr at en kan lage 63 x 15 = 1023 unike koder, nok til å gi hver lokalitet i Norge en unik kode. Vi konkluderer med at merking med naturlige geoelementer er en mulig løsning for å merke oppdrettsfisk. 94$US per fisk og med mulighet til å spore den tilbake til de 63 største produsentene. Dobbelmerking gir mulighet for sporing tilbake til lokalitet

Effects of laboratory salmon louse infection on mortality, growth, and sexual maturation in Atlantic salmon

Elevated salmon louse infection pressure generated by salmon farming represents a major threat for wild Atlantic salmon (Salmo salar). This study explored the effect of salmon lice on mortality, and body and gonad growth in F1 wild Atlantic salmon. Mature males (jacks) and immature fish were either infected with two different louse infection intensities (LIIs, 0.08 or 0.35 lice g−1) or kept as uninfected controls. Fish maturation was thereafter environmentally stimulated in seawater, followed by transfer to freshwater for 38 d to simulate river ascendance. No females matured, while 99% of the initially immature males started puberty. Jacks had high, and immature and maturing fish low, seawater mortality, independent of lice. The parasites had an LII-dependent negative effect on growth in length, weight, and condition factor in seawater. In freshwater, after the lice had detached, fish that were previously infected in seawater had reduced growth in length but not weight when compared to the uninfected control. The parasites did not affect relative gonad size in any fish phenotypes. The present results show that Atlantic salmon has a complex, and unexplored, regulation of growth when recovering from lice infection under laboratory settings. Further, the results suggest that possible negative effects of salmon louse on reproductive success in Atlantic salmon is most likely governed by the reduced body size and condition. However, further work on possible effects of salmon louse on semen quality is encouraged.publishedVersio

The culturable intestinal microbiota of triploid and diploid juvenile Atlantic salmon (Salmo salar) - a comparison of composition and drug resistance

<p>Abstract</p> <p>Background</p> <p>With the increased use of ploidy manipulation in aquaculture and fisheries management this investigation aimed to determine whether triploidy influences culturable intestinal microbiota composition and bacterial drug resistance in Atlantic salmon (<it>Salmo salar</it>). The results could provide answers to some of the physiological differences observed between triploid and diploid fish, especially in terms of fish health.</p> <p>Results</p> <p>No ploidy effect was observed in the bacterial species isolated, however, triploids were found to contain a significant increase in total gut microbiota levels, with increases in <it>Pseudomonas </it>spp., <it>Pectobacterium carotovorum</it>, <it>Psychrobacter </it>spp., <it>Bacillus </it>spp., and <it>Vibrio </it>spp., (12, 42, 9, 10, and 11% more bacteria in triploids than diploids, respectively), whereas a decrease in <it>Carnobacterium </it>spp., within triploids compared to diploids was close to significant (8% more bacteria in diploids). With the exception of gentamicin, where no bacterial resistance was observed, bacterial isolates originating from triploid hosts displayed increased resistance to antibacterials, three of which were significant (tetracycline, trimethoprim, and sulphonamide).</p> <p>Conclusion</p> <p>Results indicate that triploidy influences both the community and drug resistance of culturable intestinal microbiota in juvenile salmon. These results demonstrate differences that are likely to contribute to the health of triploid fish and have important ramifications on the use of antibacterial drugs within aquaculture.</p

A comparison of triploid and diploid Atlantic salmon (Salmo salar) performance and welfare under commercial farming conditions in Norway

Avoiding genetic interactions between wild and farmed Atlantic salmon is regarded as one of the major requirements for a sustainable salmon aquaculture industry. For this reason, farming functional sterile triploids has been suggested as a possible solution. However, knowledge about how triploids cope under commercial conditions is lacking. In the present study, we compared the performance of diploid and triploid Atlantic salmon among four Norwegian aquaculture companies. Diploid and triploid groups of the same genetic line were farmed in western, mid, and northern Norway under commercial conditions from seawater transfer until slaughter.Overall, triploid salmon exhibited reduced survival, higher incidence of emaciated fish, and scored, on average, a lower quality rating during primary processing. The results highlight the need for further research on how to improve the welfare and performance of triploid salmon in commercial aquaculture operations.publishedVersio

Adaptive photoperiod interpretation modulates phenological timing in Atlantic salmon

Photoperiod, the portion of 24-h cycle during which an organism is exposed to illumination, is an important phenological cue in many animals. However, despite its influence on critical biological processes, there remain many unknowns regarding how variations in light intensity translate into perceived photoperiod. This experiment examined how light intensity variations affect perceived photoperiod in Atlantic salmon (Salmo salar) to determine whether photoperiod interpretation is, a) fixed such that anything above a minimum detection threshold is regarded as ‘illumination’, or b) adaptive and varies with recent light exposure. To do this we compared the frequency of smoltification and sexual maturation between groups of male parr which were exposed to one of eight light regimes on a 12:12 cycling regime (12-hour day/12-hour night). The eight regimes were divided into two treatments, four with ‘High’ daytime light intensity and four with ‘Low’ daytime light intensity. The ‘High' and ‘Low' intensity treatments were each sub-divided into four groups for which the subjective ‘night’ light intensity was 100%, 10%, 1% and 0% of the daytime light intensity, with four replicate tanks of each treatment. The results show that above a minimum detection threshold, Atlantic salmon have adaptive photoperiod interpretation which varies with recent light exposure, and that adaptive photoperiod interpretation modulates the timing of the parr-smolt transformation and sexual maturation. Further, we show that photoperiod interpretation varies between closely related families. Given the influence of phenological timing on species survival, our results reveal a critical role for integration of photoperiod interpretation in attempts to understand how geographically shifting thermal niches due to climate change will affect future populations.publishedVersio