Comparative seawater performance and deformity prevalence in out-of-season diploid and triploid Atlantic salmon (Salmo salar) post-smolts

Growth performance, reproductive status, and chromosomal instability in triploid Nile tilapias

Reproductive control is one of the biggest challenges in tilapia production and triploidy was developed as an alternative to sterilization. In general, polyploids present chromosomal instability but for triploid Nile tilapia it has yet to be reported. This study evaluated the chromosomal instability from juveniles to adulthood, growth performance and gonadal status of tilapia hatched from eggs submitted or not to heat shock for triploid induction. Nile tilapia oocytes were fertilized (1,476 oocytes), half of the eggs were subjected to a four-minute shock in 41 °C water four minutes after fertilization and the other half were not (Control group). The eggs were incubated (at 27°C) and 160 larvae from the treated group hatched and survived after yolk sac absorption. The determination of ploidy was performed by flow cytometry at 85th (juveniles) and 301st (adults) days of age post yolk sac absorption. At the time of the first cytometry analysis there were 73 surviving juveniles from the treated group, and only 14 were confirmed triploid. However, at the analysis of adult ploidy, one out of 8 surviving adult tilapias from the 14 confirmed triploid juveniles remained triploid. Gonadal histology showed that the non-remaining triploids continued to produce gametes. The growth performance of triploid tilapia was initially superior to that of diploid tilapia during the juvenile phase, but similar in adults. Once the chromosome sets are lost and the tilapias become diploid again, at least in tissues with a high proliferation rate, such as the hematopoietic tissue that was analyzed (and possibly in gonads), all possible advantages of triploids are probably lost. Thus, our results suggest that, due to genomic instabilities, the triploid generation of tilapia has low efficiency.

Comparison of Diploid and Triploid Atlantic Salmon (Salmo salar) Physiological Embryonic Development

Diploid and triploid Atlantic salmon show distinct physiological differences including heart, brain, and digestive system morphology, propensity for certain deformities, temperature tolerance as eggs and once hatched, and different nutritional requirements. Whilst several studies have looked in detail at the rate of embryogenesis in diploid salmon, no study has compared the rate of embryogenesis between ploidies from fertilisation to hatch. This study based its assessment on a seminal paper by Gorodilov (1996) and used the same techniques to compare the rate at which triploid and diploid embryos developed morphological characteristics. Whilst no significant difference was found, this study provides well-needed justification for the assumption that both ploidies develop at the same rate and gives scientific weight to studies which involve manipulation at these stages of development. Two factors that did differ, however, were the timing of hatch, and mortality. Triploids hatched more quickly than diploids and reached 50% hatch at a significantly earlier point. Triploids also suffered from a significantly higher rate of mortality.

Comparative analysis of intestinal microbiota composition and transcriptome in diploid and triploid Carassius auratus

Polyploidy and the microbiome are crucial factors in how a host organism responds to disease. However, little is known about how triploidization and microbiome affect the immune response and disease resistance in the fish host. Therefore, this study aims to identify the relationship between intestinal microbiota composition, transcriptome changes, and disease resistance in triploid Carassius auratus (3nCC). In China's central Dongting lake water system, diploid (2nCC) and triploid Carassius auratus were collected, then 16S rRNA and mRNA sequencing were used to examine the microbes and gene expression in the intestines. 16S rRNA sequencing demonstrated that triploidization altered intestinal richness, as well as the diversity of commensal bacteria in 3nCC. In addition, the abundance of the genus Vibrio in 3nCC was increased compared to 2nCC (P < 0.05). Furthermore, differential expression analysis of 3nCC revealed profound up-regulation of 293 transcripts, while 324 were down-regulated. Several differentially expressed transcripts were related to the immune response pathway in 3nCC, including NLRP3, LY9, PNMA1, MR1, PELI1, NOTCH2, NFIL3, and NLRC4. Taken together, triploidization can alter bacteria composition and abundance, which can in turn result in changes in expression of genes. This study offers an opportunity for deciphering the molecular mechanism underlying disease resistance after triploidization.

Effects of ploidy and salmonid alphavirus infection on the skin and gill microbiome of Atlantic salmon (Salmo salar)

The microbial communities that live in symbiosis with the mucosal surfaces of animals provide the host with defense strategies against pathogens. These microbial communities are largely shaped by the environment and the host genetics. Triploid Atlantic salmon (Salmo salar) are being considered for aquaculture as they are reproductively sterile and thus cannot contaminate the natural gene pool. It has not been previously investigated how the microbiome of triploid salmon compares to that of their diploid counterparts. In this study, we compare the steady-state skin and gill microbiome of both diploid and triploid salmon, and determine the effects of salmonid alphavirus 3 experimental infection on their microbial composition. Our results show limited differences in the skin-associated microbiome between triploid and diploid salmon, irrespective of infection. In the gills, we observed a high incidence of the bacterial pathogen Candidatus Branchiomonas, with higher abundance in diploid compared to triploid control fish. Diploid salmon infected with SAV3 showed greater histopathological signs of epitheliocystis compared to controls, a phenomenon not observed in triploid fish. Our results indicate that ploidy can affect the alpha diversity of the gills but not the skin-associated microbial community. Importantly, during a natural outbreak of Branchiomonas sp. the gill microbiome of diploid Atlantic salmon became significantly more dominated by this pathogen than in triploid animals. Thus, our results suggest that ploidy may play a role on Atlantic salmon gill health and provide insights into co-infection with SAV3 and C. Branchiomonas in Atlantic salmon.

Response of triploid Atlantic salmon (Salmo salar) to commercial vaccines

While triploid Atlantic salmon represent a practical and affordable solution to the issues associated with sexual maturation in the salmonid aquaculture industry, empirical evidence suggests triploids are more susceptible to disease and vaccine side-effects than diploids. With vaccination now part of routine husbandry, it is essential their response be studied to confirm their suitability for commercial production. This study tested the response of triploid and diploid Atlantic salmon to vaccination with commercially available vaccines. Triploid and diploid Atlantic salmon siblings were injected with one of three commercial vaccines (or sham-vaccinated) and monitored for performance throughout a commercial production cycle. Sampling at smolt and harvest was undertaken along with individual weight and length assessments through the cycle. Antibody response to Aeromonas salmonicida vaccination was similar in both ploidy, with a positive response in vaccine-injected fish. For both adhesions and melanin, analysis found that higher scores were more likely to occur as the anticipated severity of the vaccine increased. In addition, for adhesion scores at smolt and melanin scores at smolt and harvest, triploids were statistically more likely to exhibit high scores than diploids. Triploids maintained a significantly higher body weight during freshwater and until 11 months post-seawater transfer, with diploids weighing significantly more at harvest. Growth, represented by thermal growth coefficient (TGC), decreased in both ploidy as the severity of adhesions increased, and regression patterns did not differ significantly between ploidy. Vertebral deformity prevalence was consistently higher in triploids (smolt 12.3 ± 4.5%; harvest 34.9 ± 5.9%) than diploids (smolt 0.8 ± 0.5%; harvest 15.9 ± 1.9%), with no significant difference between vaccine groups in each ploidy. This study demonstrates that triploids respond as well to vaccination as diploids and provides further supporting evidence of triploid robustness for commercial aquaculture.

Pressure shock triploidization of Salmo trutta f. lacustris and Salvelinus umbla eggs and its impact on fish development

The study tested the efficiency of hydrostatic pressure triploidization methods for Salmo trutta f. lacustris and Salvelinus umbla and investigated the effects on survival rate, skeletal malformation, and on morphometrics and cellular composition of gills, spleen, liver, kidney, intestine, and blood. In Salmo trutta f. lacustris a 100% triploidy rate in combination with high larvae survival rate (80% in comparison to control) was obtained when treating eggs with a pressure of 66 × 10³ kPa 360 °C temperature minutes (CTM) post fertilization for 5 min, in Salvelinus umbla with a similar pressure after 270 CTM. Juvenile triploid Salmo trutta f. lacustris and Salvelinus umbla (145 days post hatch) had neither an increased rate of mortality, nor an increased rate of malformations. In triploid Salmo trutta f. lacustris and Salvelinus umbla the erythrocyte volume was 50% higher and the erythrocyte concentration in peripheral blood 25-35% lower relative to diploids. In triploids also the erythrocytes surface area: volume ratio was reduced. Gills of triploid Salmo trutta f. lacustris and Salvelinus umbla had increased width of primary lamellae and increased length of secondary lamellae which might compensate for unfavorable erythrocytes surface area: volume ratio. Length of the digestive tract and histology of kidney, liver, spleen, and gills were only investigated in Salmo trutta f. lacustris. In triploids the hematopoietic tissue of the kidney was decreased by 12%, the spleen index by 53%, and the erythroblast concentrations of the spleen by 42% relative to diploids, possibly indicating reduced erythropoiesis. Length of the digestive tract and cellular arrangement of intestine, liver, and gills were not affected. In summary, the used triploidization procedure seems a reliable method not counteracting the principles of animal welfare.

Impact of dietary phosphorous in diploid and triploid Atlantic salmon (Salmo salar L.) with reference to early skeletal development in freshwater

In order to assess the effect of dietary phosphorus (P) in reducing vertebral malformations and improving freshwater (FW) performance in triploid Atlantic salmon (Salmo salar), both triploid and diploid Atlantic salmon were fed three different dietary P inclusion levels (low: 4.9, medium: 7.7, and high: 9.7 g available P kg^-1) from first feeding until smolt. Somatic and skeletal response was assessed at fry (~0.5 g), parr (~5 g) and smolt (~45 g) stages. Triploid parr initially grew faster on the high P diet, while groups fed low P resulted in a significantly higher weight at smolt. Image analysis of double stained Alcian blue and Alizarin red S fry revealed that low P fed triploid fish presented less well mineralised vertebrae, and significantly more malformed vertebrae in both parr and smolt stages following x-ray radiographic assessment. Triploid parr fed high and medium P had similar numbers of malformed vertebrae relative to their diploid counterparts but greater numbers than at smolt. Low P fed triploids had the highest prevalence of jaw and vertebral malformations as well as the highest number of deformed vertebrae in the central caudal vertebral region, which was more pronounced at parr than at smolt. Shorter vertebrae dorso-ventral lengths were observed throughout the spinal column (R1-R4) in parr fed low P and only in the caudal region (R3) at smolt. In parr, both ploidies showed reduced phosphate homeostasis protein fgf23 gene expression in vertebrae when fed low P diets, while triploids showed greater down-regulation of osteogenic factors (alp, opn and igf1r) between diets relative to diploids, suggesting possible greater active suppression of mineralisation and reduced osteogenic potential in triploids. No effects of diet or ploidy on gene expression were evident at smolt. Comparisons between development stages suggest early P supplementation in triploids is crucial for skeletal development. Ultimately, reducing vertebral deformities observed at smolt with higher P supplementation in triploids could contribute towards improving skeletal performance and welfare of the stocks in the marine phase.

Impact of Salmonid alphavirus infection in diploid and triploid Atlantic salmon (Salmo salar L.) fry

With increasing interest in the use of triploid salmon in commercial aquaculture, gaining an understanding of how economically important pathogens affect triploid stocks is important. To compare the susceptibility of diploid and triploid Atlantic salmon (Salmo salar L.) to viral pathogens, fry were experimentally infected with Salmonid alphavirus sub-type 1 (SAV1), the aetiological agent of pancreas disease (PD) affecting Atlantic salmon aquaculture in Europe. Three groups of fry were exposed to the virus via different routes of infection: intraperitoneal injection (IP), bath immersion, or cohabitation (co-hab) and untreated fry were used as a control group. Mortalities commenced in the co-hab challenged diploid and triploid fish from 11 days post infection (dpi), and the experiment was terminated at 17 dpi. Both diploid and triploid IP challenged groups had similar levels of cumulative mortality at the end of the experimental period (41.1% and 38.9% respectively), and these were significantly higher (p < 0.01) than for the other challenge routes. A TaqMan-based quantitative PCR was used to assess SAV load in the heart, a main target organ of the virus, and also liver, which does not normally display any pathological changes during clinical infections, but exhibited severe degenerative lesions in the present study. The median viral RNA copy number was higher in diploid fish compared to triploid fish in both the heart and the liver of all three challenged groups. However, a significant statistical difference (p < 0.05) was only apparent in the liver of the co-hab groups. Diploid fry also displayed significantly higher levels of pancreatic and myocardial degeneration than triploids. This study showed that both diploid and triploid fry are susceptible to experimental SAV1 infection. The lower virus load seen in the triploids compared to the diploids may possibly be related to differences in cell metabolism between the two groups, however, further investigation is necessary to confirm this and also to assess the outcome of PD outbreaks in other developmental stages of the fish when maintained in commercial production systems.

Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt

The aim of the present study was to investigate cataract development in diploid (2N) and triploid (3N) Atlantic salmon smolts and post-smolts at two water temperatures (10 and 16 °C) given diets with different histidine supplementation (LH, 10.4 and HH, 13.1 g kg^-1 ) before and after seawater transfer. In freshwater, a severe cataract outbreak was recorded in both ploidies reared at 16 °C. The cataract score was significantly higher in triploids compared to diploids, and the severity was lower in both ploidies fed the HH diet. The cataract development at 10 °C was minor. Low gill Na⁺ , K⁺ -ATPase activity in fish reared at 16 °C before seawater transfer was followed by osmoregulatory stress with elevated plasma electrolyte concentrations and high mortality in sea water. Both diploids and triploids reared at 10 °C developed cataracts during the seawater period, with higher severities in triploids than diploids and a reduced severity in the fish fed the HH diet. The findings of this study demonstrate the importance of environmental conditions in the husbandry of Atlantic salmon, and particularly triploids, with regard to smoltification and adjusted diets to mitigate cataract development in fresh and sea water.

A comparison of disease susceptibility and innate immune response between diploid and triploid Atlantic salmon (Salmo salar) siblings following experimental infection with Neoparamoeba perurans, causative agent of amoebic gill disease

Few studies have focussed on the health and immunity of triploid Atlantic salmon and therefore much is still unknown about their response to commercially significant pathogens. This is important if triploid stocks are to be considered for full-scale commercial production. This study aimed to investigate and compare the response of triploid and diploid Atlantic salmon to an experimental challenge with Neoparamoeba perurans, causative agent of amoebic gill disease (AGD). This disease is economically significant for the aquaculture industry. The results indicated that ploidy had no significant effect on gross gill score or gill filaments affected, while infection and time had significant effects. Ploidy, infection and time did not affect complement or anti-protease activities. Ploidy had a significant effect on lysozyme activity at 21 days post-infection (while infection and time did not), although activity was within the ranges previously recorded for salmonids. Stock did not significantly affect any of the parameters measured. Based on the study results, it can be suggested that ploidy does not affect the manifestation or severity of AGD pathology or the serum innate immune response. Additionally, the serum immune response of diploid and triploid Atlantic salmon may not be significantly affected by amoebic gill disease.

Ploidy elicits a whole-genome dosage effect: growth of triploid Atlantic salmon is linked to the genetic origin of the second maternal chromosome set

Background

The Atlantic salmon aquaculture industry is investigating the feasibility of using sterile triploids to mitigate genetic interactions with wild conspecifics, however, studies investigating diploid and triploid performance often show contrasting results. Studies have identified dosage and dosage-compensation effects for gene expression between triploid and diploid salmonids, but no study has investigated how ploidy and parent-origin effects interact on a polygenic trait in divergent lines of Atlantic salmon (i.e. slow growing wild versus fast growing domesticated phenotype). This study utilised two experiments relating to the freshwater growth of diploid and triploid groups of pure wild (0% domesticated genome), pure domesticated (100% domesticated genome), and F1 reciprocal hybrid (33%, 50% or 66% domesticated genome) salmon where triploidy was either artificially induced (experiment 1) or naturally developed/spontaneous (experiment 2).

Results

In both experiments, reciprocal hybrid growth was influenced by the dosage effect of the second maternal chromosome, with growth increasing as ploidy level increased in individuals with a domesticated dam (from 50% to 66% domesticated genome), and the inverse in individuals with a wild dam (from 50% to 33% domesticated genome).

Conclusions

We demonstrate that the combined effect of ploidy and parent-origin on growth, a polygenic trait, is regulated in an additive pattern. Therefore, in order to maximise growth potential, the aquaculture industry should consider placing more emphasis on the breeding value of the dam than the sire when producing triploid families for commercial production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-017-0502-x) contains supplementary material, which is available to authorized users.

Concurrence of lower jaw skeletal anomalies in triploid Atlantic salmon (Salmo salar L.) and the effect on growth in freshwater

Triploid Atlantic salmon populations are associated with higher prevalence of lower jaw skeletal anomalies affecting fish performance, welfare and value deleteriously. Anomalous lower jaw can be curved downward (LJD), shortened (SJ) or misaligned (MA). Two separate groups of triploid Atlantic salmon (~12 g) with either normal lower jaw (NOR) or SJ were visually assessed four times over three months for presence and concurrence of jaw anomalies (with severity classified) and opercular shortening to understand the relatedness of these anomalous developmental processes. The prevalence of jaw anomalies increased in both groups over time (NOR group - SJ, LJD and MA combined 0-24.5%; SJ group - LJD and MA combined 17-31%). SJ and LJD occurred both independently and concurrently whereas MA exclusively concurred with them. All three anomalies could be concurrent. Severity of both LJD and SJ increased in the SJ group only. Opercular shortening recovery was observed in both groups but at a slower rate in the SJ group. The SJ group specific growth rate (SGR) was significantly (P < 0.05) lower than the NOR group. This study demonstrated the concurrence of SJ, LJD and MA and showed possible deleterious consequences deriving from the conditions.

Skeletal anomaly assessment in diploid and triploid juvenile Atlantic salmon (Salmo salar L.) and the effect of temperature in freshwater

Triploid Atlantic salmon tend to develop a higher prevalence of skeletal anomalies. This tendency may be exacerbated by an inadequate rearing temperature. Early juvenile all-female diploid and triploid Atlantic salmon were screened for skeletal anomalies in consecutive experiments to include two size ranges: the first tested the effect of ploidy (0.2-8 g) and the second the effect of ploidy, temperature (14 °C and 18 °C) and their interaction (8-60 g). The first experiment showed that ploidy had no effect on skeletal anomaly prevalence. A high prevalence of opercular shortening was observed (average prevalence in both ploidies 85.8%) and short lower jaws were common (highest prevalence observed 11.3%). In the second experiment, ploidy, but not temperature, affected the prevalence of short lower jaw (diploids > triploids) and lower jaw deformity (triploids > diploids, highest prevalence observed 11.1% triploids and 2.7% diploids) with a trend indicating a possible developmental link between the two jaw anomalies in triploids. A radiological assessment (n = 240 individuals) showed that at both temperatures triploids had a significantly (P < 0.05) lower number of vertebrae and higher prevalence of deformed individuals. These findings (second experiment) suggest ploidy was more influential than temperature in this study.

The frequency of spontaneous triploidy in farmed Atlantic salmon produced in Norway during the period 2007-2014

BACKGROUND

Spontaneous triploidy has been reported in a number of fish species, and is often linked with in vivo or in vitro ageing of eggs post ovulation. Here, we provide the first investigation into the frequency of spontaneous triploidy in farmed Atlantic salmon by analysing more than 4000 fish from 55 farms, and approximately 1000 recaptured escapees, all sampled in the period 2007-2014. In addition, we compare microsatellite genotyping against flow cytometry and red blood cell diameter in a set of 45 putatively diploid and 45 putatively triploid Atlantic salmon.

RESULTS

The three methods implemented for ploidy determination gave consistent results, thus validating the methods used here. Overall, 2.0% spontaneous triploids were observed in salmon sampled on farms. The frequency of spontaneous triploids varied greatly among sea cages (0-28%), but they were observed in similar frequencies among the three primary breeding companies (1.8-2.4%). Spontaneous triploids were observed in all farming regions in Norway, and in all years sampled. Spontaneous triploids were also observed among the escapees recaptured in both the marine environment and in rivers.

CONCLUSIONS

Spontaneous triploidy in commercially produced Atlantic salmon is likely to be a result of the practices employed by the industry. For logistical reasons, there is sometimes a pause of hours, and in some cases overnight, between killing the female broodfish, removal of her eggs, and fertilization. This gives the eggs time to age post ovulation, and increases the probability of duplication of the maternal chromosome set by inhibition of the second polar body release after normal meiosis II in the oocyte.

Vaccination and triploidy increase relative heart weight in farmed Atlantic salmon, Salmo salar L

Heart morphology is particularly plastic in teleosts and differs between farmed and wild Atlantic salmon. However, little is known about how different culture practices and sex affect heart morphology. This study investigated how vaccination, triploidy and sex affected heart size and heart morphology (ventricle shape, angle of the bulbus arteriosus) in farmed Atlantic salmon for 18 months following vaccination (from c. 50-3000 g body weight). In addition, hearts were examined histologically after 7 months in sea water. All fish sampled were sexually immature. Vaccinated fish had significantly heavier hearts relative to body weight and a more triangular ventricle than unvaccinated fish, suggesting a greater cardiac workload. Irrespective of time, triploids had significantly heavier hearts relative to body weight, a more acute angle of the bulbus arteriosus and less fat deposition in the epicardium than diploids. The ventricle was also more triangular in triploids than diploids at seawater transfer. Sex had transient effects on the angle of the bulbus arteriosus, but no effect on relative heart weight or ventricle shape. From a morphological perspective, the results indicate that vaccination and triploidy increase cardiac workload in farmed Atlantic salmon.

The prevalence of vertebral deformities is increased with higher egg incubation temperatures and triploidy in Atlantic salmon Salmo salar L

Suboptimal egg incubation temperature is a risk factor for the development of skeletal deformities in teleosts. Triplicate diploid and triploid Atlantic salmon, Salmo salar L., egg batches were incubated at 6, 8 and 10 °C up until first feeding, whereupon fish were reared on a natural temperature before examination for externally visible skeletal deformities (jaw and spine) and radiographed for vertebral deformities and morphology at the parr stage. Increasing incubation temperatures and triploidy increased the number of fish showing one or more deformed vertebrae. Triploids had significantly higher mean vertebrae cranio-caudal length (L) and dorsal-ventral height (H) ratio at 6 and 10 °C than diploids, but triploidy had no effect on mean vertebrae centra area. Triploids demonstrated an increase in lower jaw deformities with increased incubation temperature, whereas jaw deformities were rare in diploids. Fish incubated at 10 °C had a significantly lower mean vertebral number than fish incubated at 6 °C, and triploids had lower mean vertebral numbers than diploids. Diploid fish with 58 vertebrae had a significantly higher mean vertebral centra area than fish with 59 vertebrae, but vertebral number did not affect the mean vertebral L/H ratio. The results are discussed with respect to the welfare and production of farmed salmonids.

Triploid and diploid Atlantic salmon show similar susceptibility to infection with salmon lice Lepeophtheirus salmonis

BACKGROUND

Sea lice infection is the most expensive disease factor for Atlantic salmon sea-cage farming. For triploid salmon to be accepted as a commercial possibility, investigation of susceptibility of triploid salmon to sea lice infection is a fundamental milestone. The susceptibility of diploid and triploid salmon to infection with Lepeophtheirus salmonis was examined in a tank trial in Scotland, a tank trial in Norway and a cage trial in Scotland.

RESULTS

Following a single infection challenge, results indicated a significant correlation between fish size and the number of attached sea lice. Triploid fish were larger than diploids at the smolt stage. In the tank trials, no difference was found between infection levels on diploids and triploids after a single infection challenge. The tank trial in Scotland continued with a second infection challenge of the same fish, which also showed no infection differences between ploidies. A borderline correlation between first infection and re-infection intensity was found for PIT-tagged diploid salmon examined after each challenge. No significant difference in louse infection between diploid and triploid salmon (∼2 kg) was found in the cage trial undertaken under commercial conditions.

CONCLUSION

This study concludes that triploid Atlantic salmon are not more susceptible to sea louse infection than diploid fish.

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.

The effect of ploidy and incubation temperature on survival and the prevalence of aplasia of the septum transversum in Atlantic salmon, Salmo salar L

Heart deformities are a concern in aquaculture and are linked to egg incubation temperature. Diploid and triploid Atlantic salmon, Salmo salar L., were incubated at 6, 8 and 10 °C and analysed for aplasia of the septum transversum (n = 150 ploidy⁻¹ incubation temperature⁻¹). Heart morphology (size and shape) was assessed in fish incubated at 6 °C and in fish with and without aplasia of the septum transversum (n = 9 group⁻¹) incubated at 10 °C. Egg mortality was significantly higher in triploids than in diploids at all incubation temperatures, and increased egg incubation temperatures increased mortality in both ploidy. Triploids grew quicker than diploids after egg incubation at 10 °C, but not at 6 °C. Aplasia of the septum transversum occurred only in triploid fish after incubation at 6 °C and 8 °C (0.7% and 3.3%, respectively) and was significantly greater (P ≤ 0.05) in triploids after incubation at 10 °C compared with diploids (30% and 18%, respectively). Aplasia of the septum transversum significantly increased heart mass and resulted in a long flat ventricle compared with fish displaying a septum transversum. The results suggest triploid salmon should be incubated below 8 °C.

Growth and gonadal development in diploid and triploid Atlantic cod (Gadus morhua)

Induction of triploidy has been suggested as an effective tool to prevent spawning of farmed fish. This experiment examined the growth potential of triploid cod when reared communally with diploid ones after the juvenile stage. Pressure treatment was used to induce triploidy in a batch of cod eggs in April 2009. The resulting offspring were reared separately from their diploid counterparts until they reached the proper size for PIT tagging. At the age of 8 months, an equal number of 115 diploids (135.5 ± 3.95 g) and triploids (93.6 ± 2.63 g) were communally reared in a circular flow-through tank until the age of 22 months. By the end of this rearing period, diploids (1,002.4 ± 39.9 g) were significantly heavier than triploids (654.6 ± 27.7 g), but the specific growth rate did not differ significantly during the growth trial. Gonadal development at the age of 22 months was also lower among triploids than diploids, especially for females (5.3 and 91.9 %) but also for males (32.5 and 72.7 %). Sterility among female triploids was evident by the reduced size and dysfunctional gonads, but gonadal development in male triploids was less suppressed. Prevalence of body deformities was, however, significantly higher among triploids (62.6 %) than diploids (33.9 %). Higher prevalence of deformities in triploid cod underlines the need for further fine-tuning of the triploidization procedure or finding other methods of sterilization. At present, triploid cod are still far from being established as an alternative for commercial production.

The effect of triploidy and vaccination on neutrophils and B-cells in the peripheral blood and head kidney of 0+ and 1+ Atlantic salmon (Salmo salar L.) post-smolts

Sterile triploid fish are being used in aquaculture to prevent early unwanted sexual maturation and the genetic interaction between wild and cultured fish; however, triploid fish are typically considered to be more susceptible to disease than diploid counterparts. Proportions of leucocytes from the head kidney and peripheral blood were identified using monoclonal antibodies and flow cytometry in triploid and diploid, vaccinated and unvaccinated, out-of-season (0+) and 1+ Atlantic salmon (Salmo salar L.) three weeks post seawater transfer. Triploid 1+ fish were significantly (P<0.05) heavier than diploid fish at the time of sampling, whereas triploid 0+ had a significantly lower condition factor than diploids. Ploidy had a significant effect on the proportion of B-cells in the blood of both 0+ and 1+ fish, and the head kidney of 1+ fish, with triploids having lower proportions of B-cells to diploids in both smolt groups. In addition, a significant ploidy×vaccination interaction effect was observed in the response of neutrophils in the blood (vaccinated diploids had a higher mean proportion than diploid unvaccinated) and B-cells in the head kidney (in vaccinated fish, triploids had a lower mean proportion than diploids) in 0+ smolts. Vaccination was found to significantly increase the proportion of B-cells in the head kidney of 1+ smolts in both ploidy. Size (fish weight) was positively correlated with neutrophil proportions in 1+ fish. Our findings are discussed in relation to the physiological differences related to ploidy. The results suggest that ploidy as well as smelting regime influences the immune system of Atlantic salmon post-smolts.

Lumican is a major small leucine-rich proteoglycan (SLRP) in Atlantic cod (Gadus morhua L.) skeletal muscle

Knowledge on fish matrix biology is important to ensure optimal fish -quality, -growth and -health in aquaculture. The aquaculture industry face major challenges related to matrix biology, such as inflammations and malformations. Atlantic cod skeletal muscle was investigated for collagen I, decorin, biglycan, and lumican expression and distribution by real-time PCR, immunohistochemical staining and Western blotting. Immunohistochemical staining and Western immunoblotting were also performed using antibodies against glycosaminoglycan side chains of these proteoglycans, in addition to fibromodulin. Real-time PCR showed highest mRNA expression of lumican and collagen I. Collagen I and proteoglycan immunohistochemical staining revealed distinct thread-like structures in the myocommata, with the exception of fibromodulin, which stained in dense structures embedded in the myocommata. Chondroitinase AC-generated epitopes stained more limited than cABC-generated epitopes, indicating a stronger presence of dermatan sulfate than chondroitin sulfate in cod muscle. Lumican and keratan sulfate distribution patterns were strong and ubiquitous in endomysia and myocommata. Western blots revealed similar SLRPs sizes in cod as are known from mammals. Staining of chondroitin/dermatan sulfate epitopes in Western blots were similar in molecular size to those of decorin and biglycan, whereas staining of keratan sulfate epitopes coincided with expected molecular sizes of lumican and fibromodulin. In conclusion, lumican was a major proteoglycan in cod muscle with ubiquitous distribution overlapping with keratan sulfate. Other leucine-rich proteoglycans were also present in cod muscle, and Western blot using antibodies developed for mammalian species showed cross reactivity with fish, demonstrating similar structures and molecular weights as in mammals.