Deformities In Atlantic Salmon Research Articles

Vertebra deformities in wild Atlantic salmon caught in the Figgjo River, southwest Norway

Summary In order to investigate the occurrence of vertebra deformities in wild Atlantic salmon, adult river migrating salmon were caught in the Figgjo River, Norway in 2010, 2011 and 2012 (n = 24; 21; 20). Based on a definition of a deformed fish having one or more deformed vertebrae, 28 out of 65 fish were classified as deformed. The majority were minor deviations of the morphology in vertebra no 2 and in vertebrae in the ural region (52–56). Vertebral fusions were observed, the majority of which were located in the post-cranial and posterior-truncal region of the vertebral column. Fusions typically resulted in a single large vertebra with a relatively normal amphicoelous structure, albeit with multiple neural and hemal arches. This indicates that wild salmon have a strong capability of ‘repairing’ vertebra pathologies, as this stage of a vertebra deformity should not be considered as pathological anymore. Occurrence of individuals with fusions varied over the sampling period (2010: 29%, 2011: 19%, 2012: 5%). Typical deformities observed in farmed salmon, e.g. vertebra compressions in the tail region, which often cause down-grading, financial losses and reduced welfare, were not observed in any of the analysed fish and can therefore be considered as ‘farming specific’. This is the first study of vertebra deformities in adult wild Atlantic salmon, and demonstrates that these fish can develop deformities up to a level observed in harvest-size farmed salmon. However, the severity of these malformations was found to be low compared to those commonly observed in farmed salmon. The results of this study may serve as a basis for future research on vertebra deformities in Atlantic salmon.

Vaccination and elevated dietary phosphorus reduces the incidence of early sexual maturation in Atlantic salmon (Salmo salar L.)

This study investigated the effect of ip injection of an oil-adjuvant vaccine and dietary phosphorus (P) level on the incidence of sexual maturation and occurrence of skeletal deformities in Atlantic salmon. Triplicate groups (12×12m sea cages) of vaccinated (V) and unvaccinated (UV) Atlantic salmon underyearling smolts were fed diets with 0.6% (0.6P) or 0.9% available phosphorus (0.9P) from seawater transfer in mid-October and 3months onwards, and then a commercial diet for a further 11months. Both vaccination and 0.9% available phosphorus significantly increased the proportion of immature fish. V significantly reduced the incidence of mature females, while 0.9P significantly reduced the incidence of mature males. In addition, there were always relatively fewer mature V than UV males within each of the six sea-cages (three per diet). At the end of the period on different test diets, fish fed the 0.6P diet displayed significantly lower mechanical stiffness of the vertebral bodies than fish fed the 0.9P diet, but the mean values were both relatively high, which indicated that both groups enjoyed good mineral status. There was no effect of vaccination on stiffness, and there were no dietary or vaccination effects on the occurrence of externally detectable skeletal deformities (vertebral column, operculum, jaw).This is the first study to show that dietary phosphorus and vaccination can influence sexual maturation in fish. The results show that early seawater diets for underyearling Atlantic salmon smolts must be sufficient in phosphorus to prevent unwanted sexual maturation during on-growth in seawater.

Dietary phosphorus does not reduce the risk for spinal deformities in a model of adjuvant-induced inflammation in Atlantic salmon (Salmo salar) postsmolts

Inflammation is a non-specific protective mechanism towards injury known to affect bone remodelling. This study aimed to investigate the effect of Freund’s complete adjuvant (FCA) induced-inflammation on the prevalence of spinal deformities of Atlantic salmon postsmolts fed with two different dietary P levels. Sextuple groups of salmon postsmolts were fed with either a low-phosphorous (6 g kg−1 available P, LP) or a high-phosphorous (9 g kg−1 available P) diet for a period of 101 days. On Day 102, individually tagged fish were subjected to (i) single injection with FCA (0.125 mg kg−1 BW) dissolved in phosphate-buffered saline (PBS) (ii) placebo injection with PBS or (iii) sham injection (insertion of needle only) or (iv) remained untreated. On Day 103, fish were given a common diet for 174 days in seawater. No significant differences in body weight were observed. Injected fish, particularly the FCA group, had more compressions in the injection site than untreated fish. No effect of diet and no interaction between treatment and diet were observed. Severe scoliosis was observed in ∼7% of FCA-injected individuals, corresponding to a mixture of bone malformations in the tail region. In conclusion, experimentally induced inflammation may be an independent risk factor for bone deformities in Atlantic salmon.

The effect of water temperature on vertebral deformities and vaccine-induced abdominal lesions in Atlantic salmon, Salmo salar L.

This study investigates the effects of water temperature (T) on vaccine-induced abdominal lesions (i.p. injection with oil-adjuvant vaccine) and vertebral deformities in Atlantic salmon. Quadruple groups of vaccinated (V) or unvaccinated (U) underyearling smolts were reared in tanks under four different temperature regimes for 6 weeks in fresh water (FW) followed by 6 weeks in sea water (SW). The four different T regimes were 10 °C FW-10 °C SW (10-10), 10 °C FW-16 °C SW (10-16), 16 °C FW-10 °C SW (16-10) and 16 °C FW-16 °C SW (16-16). After the temperature regimes were finished, the fish were group-tagged and transferred to a common sea cage for on-growth until harvest size. At termination, weight was significantly affected by both T and V, while lesion score and deformities were affected by T only. The weight difference between the largest and smallest U group was 20.3% (16-10 U: 2.4 kg, 10-16 U: 1.89 kg), while the largest difference between U and V fish within a T regime was 28.7% (16-16 U: 2.1 kg, 16-16 V: 1.5 kg). Fish from the 16-16, 16-10 and 10-16 regimes had a significant higher lesion score than those from the 10-10 regime. Fish from the 10-16 and 16-16 regimes displayed a significantly higher prevalence of vertebral deformities (palpation : 13-27%, radiology: 88-94%) than fish from the 10-10 and 16-10 regimes (palpation: 2-3%, radiology: 27-65%). Vertebra number 26 (located beneath the dorsal fin) was the most frequently affected vertebra in smolts, while vertebra number 43 (located above the anal fin) was most frequently affected in adults.

Vertebral body mineralization and deformities in cultured Atlantic salmon ( Salmo salar L.): Effects of genetics and off-season smolt production

The present study aimed to investigate whether genetic background in combination with the development of more intensive production regimes influences bone mineralization and the development of vertebral deformities in cultured Atlantic salmon. Triplicate salmon parr groups of wild, farmed, and hybrid origin (here-on referred to as wild, farmed and hybrid genotypes) were reared as underyearling (0+, SW transfer 8 months post hatching in Jan 2006) or yearling smolt (1+, SW transfer 12.5 months post hatching in May 2006), and evaluated for vertebral mineralization (mineral content, as % of bone dry weight; n = 90; 15 per group) and deformities (radiology; n = 540; 90 per group) in March 2007. Farmed fish (0+ 2.5 kg, 1+ 2.1 kg) were significantly larger than wild (0+ 0.9 kg, 1+ 0.8 kg) and hybrid (0+ 1.5 kg, 1+ 1.3 kg) fish. Bone mineral content in the vertebrae was significantly higher in farmed (57.6%) than in hybrid (57.2%) and wild (56.5%) fish, and significantly higher in hybrid than in wild fish within the 1+ smolt, whereas there were no differences in the mineral content between genotypes within the 0+ smolt, or effect of production strategy within each genotype. The prevalence of deformed fish (% individuals with one or more deformed vertebrae) ranged from 6.6% and 17.1%, but there were no significant effect of genotype or production strategy. The results of the present study indicate that neither off season smoltification, smolt quality or genetic background are important factors in the etiology of vertebral deformities in farmed Atlantic salmon. The data may serve as a base-line for further studies on vertebral deformities in Atlantic salmon.

Dietary menadione nicotinamide bisulphite (vitamin K3) does not affect growth or bone health in first-feeding fry of Atlantic salmon (Salmo salarL.)

The aim of the present study was to elucidate if increasing levels of added vitamin K in the feed influenced fish growth, health or the incidences of bone deformities in Atlantic salmon (Salmo salar L.) from onset of start feeding to ∼100 g in freshwater. Duplicate groups of Atlantic salmon fry (∼0.20 g) were fed eight levels (0, 2.5, 5, 7.5, 10, 15, 20 and 50 mg menadione kg−1) of the vitamin K derivate menadione nicotinamide bisulphite (MNB) in a regression design for 28 weeks. All fish maintained high growth rates throughout the experiment, and showed no significant differences in specific growth rate, condition factor, whole body proximate analysis, blood coagulation time, vertebra morphology or mechanical properties of vertebrae. We found a dose-response between whole body vitamin K concentration and the dietary MNB supplementation level. Analysis of liver γ-glutamylcarboxylase activity revealed significant dose-dependent differences between groups given the 0, 10 and 50 mg MNB kg−1 diets. In conclusion, Atlantic salmon seems to require low levels of dietary vitamin K, and the amount of vitamin K found naturally in the presently used feed ingredients may be enough to maintain optimal growth, health and bone strength in Atlantic salmon fry from start feeding.

Association of spinal deformity and vaccine‐induced abdominal lesions in harvest‐sized Atlantic salmon, Salmo salar L.

Spinal deformities in Atlantic salmon, Salmo salar L., have been described as a disease of multifactorial origin for which vaccines and time of vaccination have been suggested as risk factors. A vaccine efficacy trial where spinal deformity became evident was continued by the observational study reported here. In the preharvest part of the study 17 months post-sea transfer, there was a prevalence of 11.3% spinal deformity, with deformities present only in one vaccine group indicating a strong vaccine involvement. At slaughter, the prevalence of spinal deformities was 11.7%, and deformed fish had only 62% of normal slaughter weight. Visual analogue scales (VAS) were used for continuous recordings of vaccine-induced abdominal lesions and deformity. A logistic regression model associating presence of spinal deformity with markers of abdominal lesions was developed. The odds ratio for spinal deformity was 5.7 (95% CI: 3.4-9.4) for each unit increase in adhesion score (0-6) and 4.9 (2.9-3.4) for each unit increase in melanin on abdominal organs (0-3). Lesions in the dorsal caudal part of the abdomen gave an odds ratio for spinal deformity of 2.2.

The aetiology of spinal deformity in Atlantic salmon, Salmo salar L.: influence of genetic factors on the frequency and severity in freshwater stages

A radiographic study was carried out on 2-year groups of pre-smolt parr to detect the comparative frequency of vertebral change in a range of defined pedigreed families of high growth rate of Atlantic salmon, Salmo salar L., reared under identical conditions. The observed frequency of deformity was related to the observed deformity level in the seawater parental generation, and to a potentially uncontrolled environmental determinant, i.e. stripping date. High and low parental deformity groups of families were found to produce offspring that had very similar levels of radiographically detectable spinal deformities in the pre-smolt parr, suggesting no genetic link. With regard to stripping date, the overall incidence was nearly half that seen in the preceding year (8.7% cf 16.6%). However, a non-significant trend to fewer radiographic spinal deformities was seen in the later stripping period.

The aetiology of spinal deformity in Atlantic salmon, Salmo salar L.: influence of different commercial diets on the incidence and severity of the preclinical condition in salmon parr under two contrasting husbandry regimes

A large-scale trial of the effect of different commercial diets on the incidence of preclinical spinal deformation, as assessed by radiography, and the influence of two contrasting rearing systems was carried out. Two sets of three populations of Atlantic salmon, each of 20 000 first feeding fry of identical hatchery origin, created from equal numbers of eggs from 15 different families, were reared under commercial conditions on two different farms. Three commercial (closed formula) extruded fish meal-based diets were used in this study (diets A, B & C). Each diet was fed to one population of 20 000 fish at each site. Fish were fed a percentage of their body weight per day, with feeding rates set at commercial levels, based on water temperature, day length and fish biomass. Additional hand feeding was used to ensure satiation in all tanks. Fish in each tank were bulk-weighed and counted at the beginning and at 2-week intervals throughout the study. The fish were grown for 30 weeks. In addition, phosphorus (P) digestibility was evaluated by in-feed absorption testing in rainbow trout. The morphology of the radiographic lesions conformed to those described previously. Statistical analysis using multivariate regression analysis showed that date of sampling, site and diet were all statistically significant (P < 0.001) on univariable analysis. Farm A had significantly more affected fish than farm B (P < 0.001), which may have been attributable to variation in dissolved oxygen levels. The available dietary P levels were low in each diet. The number of fish affected in the group of fish being fed diet B was significantly lower than in the groups being fed diets A or C (P < 0.001). It appears most likely that the occurrence of preclinical radiographically apparent defects in parr which are believed to lead to the condition known as 'spinal deformity' is predominantly caused by a deficiency of available dietary P in first-feeding fry. The availability of dietary P may also vary considerably between diets formulated using different ingredients. Phytate-P associated with plant ingredients may affect the availability of P as well as other essential dietary nutrients. Additionally, diets for the production of salmonids in fresh water are currently formulated to keep P effluent to a minimum compatible with healthy spinal development. These various factors combine to make it crucial that small Atlantic salmon, especially first-feeding fry, are provided with carefully formulated diets fortified to an adequate level with a high quality source of available P.

Effects of different genetic disposition and mineral diet, and their interaction, on the frequency of different type of skeletal deformities in Atlantic salmon

Effects of different genetic disposition and mineral diet, and their interaction, on the frequency of different type of skeletal deformities in Atlantic salmon

Cloning and characterization of the executioner caspases 3, 6, 7 and Hsp70 in hyperthermic Atlantic salmon ( Salmo salar) embryos

Hyperthermia during embryogenesis has been reported to induce deformities in Atlantic salmon ( Salmo salar). To examine the involvement of executioner caspases in hyperthermia-induced cell-death in a poikilotherm vertebrate species, five genes encoding caspase-3,-6, and -7 were cloned from Atlantic salmon, and the expression was studied in thermal stressed salmon embryos. The salmon genome contained two genetically distinct variants of both salmon caspase-3 and caspase-6 that is likely the result of two independent chromosome or genome duplications. Whereas only partial caspase-3A encoding sequences were isolated, the full-length caspase-3B cDNA encodes the inactive proenzyme of 279 amino acids (aa) consisting of an N-terminal prodomain and the large and the small subunit. The salmon caspase-6A and caspase-6B proenzymes include an additional linker region between the two subunits. The deduced salmon caspase-7 consists of only 245 aa and lacks the prodomain and part of the large subunit similar to the predicted caspase-7 of the puffer fish Tetraodon sp.. Increased apoptotic activity as evidenced by cleavage of nuclear DNA was demonstrated in salmon embryos incubated at 18–20 °C for 84 h after acclimatization at 8 °C. Hyperthermia-induced activation of the executioner caspases was indicated by the increased mRNA levels of caspase-3B, caspase-6A/B and caspase-7 after 54 h heat exposure as quantified by real-time RT-PCR. The 2–2.5 fold increase in the mRNA expression of the heat shock protein Hsp70 gene coincided with the peak mRNA values of the executioner caspases. Whole-mount in situ hybridization of the salmon embryo identified caspase-7 mRNA in the lens exclusively, while caspase-3B and caspase-6A/B were expressed in multiple tissues of exposed and control embryos. Interestingly, cardiac expression of caspase-6A/B was only identified in heat stressed embryos . Altogether, these results shed light on evolutionary aspects of the executioner caspases in vertebrates and their expression in salmon embryos exposed to hyperthermia. In particular, the heat sensitive caspase-6 expression in the embryonic heart is of interest since cardiac malformations are an emergent problem in salmon aquaculture.

Genetic variation for a vertebral deformity in Atlantic salmon ( Salmo salar)

The incidence of vertebral deformities was observed on a total of 44,684 offspring of 225 sires and 471 dams from four different year-classes (hatched in 1992, 1993, 1994 and 1995) of Atlantic salmon ( Salmo salar). The deformities, observed on ungutted fish at different farms, were classified as humpback anterior or posterior dorsal fin or a shortened tail. The average incidence of fish with vertebral deformations was 9.5%, 7.6%, 21.5% and 2.3% in the four year-classes. The different water temperatures during egg incubation could not explain these incidence differences among the year-classes. Deformed fish were in general significantly lighter, shorter and had a higher and more variable condition factor than nondeformed fish within each sex-maturity category. The differences in the percentage of deformed fish between immature fish and sexually maturing males and females were not consistent over the year-classes. The magnitude of the estimated heritabilities for deformity shows that vertebral deformity is determined by a substantial additive genetic component. The heritability estimates on the liability scale were, as expected, higher than those derived from the observed scale (in parentheses); 0.36±0.14 (0.20±0.08), 0.22±0.09 (0.09±0.04), 0.25±0.12 (0.12±0.06) and 0.00±0.00 (0.00±0.00) in the four year-classes. However, the rank correlation coefficients between the estimated full-sib family breeding values for deformity on the observed and the underlying liability scale were all very high (>0.98). The genetic correlations between deformity and body weight (and body length) were negative indicating that high genetic growth potential was not the cause of the deformity, but rather a result of deformed fish being smaller. The magnitude of the correlation between the coefficient of inbreeding and the breeding values for deformity of full-sib families (ranging from −0.22 to 0.16 in the four year-classes) indicate that inbreeding did not cause the deformity problems. In view of these results, it is recommended not to select breeders from families with high incidences of deformed fish and, of course, not at all the breeders showing deformities themselves. Such a procedure is not likely to reduce the deformities significantly, but it will prevent the increase in the genetic susceptibility to vertebral deformities in the population. Further efforts should be made to explore the various aetiological causes of the deformities before further critical choices are made.

Identification of Stress Sensitive Genes in Hyperthermic Atlantic Salmon (Salmo salar) Embryos by RAP-PCR

Deformities of skeletal structures, the heart, and other organs are a recurrent problem in species used in intensive aquaculture. Elevated egg incubation temperature appears to be a high risk factor in the development of these malformations, but the causal relation has not been established. Our aim was to identify candidate genes involved in the development of heat induced deformities in Atlantic salmon (Salmo salar). Temperature sensitive genes were isolated by RNA Arbitrarily Primed (RAP)-PCR. A total of 33 RAP-PCR products were successfully sequenced, and the expression of eight identified genes was further examined by RT-PCR from pooled samples of heat exposed embryos. Five of these genes were demonstrated to be temperature sensitive, of which four were shown to be up-regulated and one was down-regulated at elevated water temperatures. The atrial natriuretic peptide (ANP) gene, which is a promising candidate for heart deformities, showed the highest level of heat induction. Three additional RAP-PCR products identified as heterogeneous nuclear ribonucleprotein (hnRNP) A0, acyl CoA binding protein (ACBP) and mitochondrial (mt)-HSP70 showed up-regulated mRNA expression in response to elevated water temperature. The single down-regulated gene was identified as an Atlantic salmon (Salmo salar) homolog of the cysteine and tyrosine-rich 1 (CYYR1) gene. This study demonstrated that a temperature elevation of only 4 °C during the early stages of the organogenesis in Atlantic salmon induce altered expression of a number of genes, which are candidates for the development of heat induced deformities.

Risk factors for spinal deformities in Atlantic salmon, Salmo salar L.

Risk factors for spinal deformities or short tails in Atlantic salmon, Salmo salar L., were examined in a cohort study in Hordaland County of Norway, in which 177 slaughter groups consisting of 5000 salmon were followed from sea water introduction in April 1994 until slaughter in February 1996. If the smolt weight increased from 0.05 to 0.1 kg, the risk of spinal deformities decreased (relative risk, RR = 0.2). An increased period from smolt vaccination to seawater introduction of from 2 to 5 months was associated with an increased risk (RR = 1.6). Salmon reared in fjord sites were at higher risk for spinal deformities (RR = 1.9) than those reared in oceanic sites, possibly due to the larger variation in salinity and temperatures in the fjord sites. Rapidly growing salmon were at lower risk of spinal deformities at slaughter (RR = 0.2), and they were likely to be slaughtered earlier, which could explain the observed lower risk for salmon slaughtered in June (RR = 0.4). Moreover, the findings concerning egg suppliers could indicate a possible role of genetic factors in the aetiology of spinal deformities.

Development of spinal deformities in Atlantic salmon and Arctic charr fed diets supplemented with oxytetracycline

Some individuals within populations of Atlantic salmon Salmo salar and Arctic charr Salvelinus alpinus fed diets supplemented with oxytetracycline (OTC) developed spinal deformations. Possible differences in feed intake and growth of spinally deformed fish relative to fish without any deformities were investigated. Amongst Atlantic salmon, 17% of the fish fed OTC-supplemented feed developed spinal fractures, whereas none of the fish receiving the basic feed did so. Despite deformation of the spinal column, the injured fish continued to feed and grow, but at lower rates than unaffected individuals. In contrast to Atlantic salmon, Arctic charr showed no signs of spinal fractures at any time during the 65-day experiment.

Development of spinal deformities in Atlantic salmon and Arctic charr fed diets supplemented with oxytetracycline

Some individuals within populations of Atlantic salmon Salmo salar and Arctic charr Salvelinus alpinus fed diets supplemented with oxytetracycline (OTC) developed spinal deformations. Possible differences in feed intake and growth of spinally deformed fish relative to fish without any deformities were investigated. Amongst Atlantic salmon, 17% of the fish fed OTC‐supplemented feed developed spinal fractures, whereas none of the fish receiving the basic feed did so. Despite deformation of the spinal column, the injured fish continued to feed and grow, but at lower rates than unaffected individuals. In contrast to Atlantic salmon, Arctic charr showed no signs of spinal fractures at any time during the 65‐day experiment.

Genetic variation for a spinal deformity in Atlantic salmon, Salmo salar

Susceptibility of a specific spinal deformity, first observed in 2 1 2 - year-old Atlantic salmon, was found to be genetically heritable. Heritabilities calculated on the observed scale were 0.25 and 0.14 based, respectively, on the sire and dam components of variance. On the underlying liability scale, the corresponding heritabilities were 0.64 and 0.36. At 3 1 2 years , deformed fish were lighter, shorter, had a higher condition factor and were more likely to be immature than unaffected fish. However, small size did not cause the deformity, but rather was a result of the deformity. The reason for the deformity could not be determined but possible causes are discussed.