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.     

Spinal deformation in commercially cultured Atlantic salmon, Salmo salar L.: a clinical and radiological study

A clinical and radiographic study was carried out on 2016 randomly selected Atlantic salmon parr from six farms, which weighed between 55 and 100 g. In addition, 86 fish from six marine farms were similarly studied. Radiographically detectable vertebral lesions were found in 3.8-8.8% of the parr. The changes ranged from a single vertebra showing features, such as demineralization, increased density and slight loss of structure, to fish with multiple vertebrae affected by collapse, fusion and change in intervertebral space that could give rise to lordosis or kyphosis or abnormal vertebrae at several locations. The predominant location was the vertebral region V21-27, and rarely V44 caudad. The radiographic changes in seawater salmon mirrored those found in parr, but vertebrae V35 caudad were more frequently involved. Very few parr were found to have abnormal vertebrae in the peduncle area which suggests that the development of lesions at this location occurs de novo in the seawater phase, given that 'stumpy' fish are most frequent reported deformity at slaughter. It was concluded that minor vertebral change could be detected radiographically in many parr with no observable effect on external morphology. Whether such minor radiographic alteration would proceed to observable morphological change at slaughter weight is open to question.     

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.     

Screamer disease in Atlantic salmon, Salmo salar L., in Chile

Investigation of cranial and spinal deformities in Atlantic salmon smolts from Chile immediately after sea transfer, over two successive crops, demonstrated ankylosis of the mandibular articulation, spinal foreshortening, fracture of vertebrae and rarefaction of osseous and cartilaginous tissues including the operculum. As a result the mouth was permanently agape and opercula could be folded back on themselves. All affected fish had been transferred to sea water at 20 °C plus and fed on particular commercial diets. Fish in cooler areas, or on diets high in vitamin C and phosphorus in the high temperature zone, were clinically normal. The condition has not recurred following dietary adjustment.     

Dietary phosphorus requirement of juvenile Atlantic salmon, Salmo salar L.

The objective of this study was to determine the dietary phosphorus (P) requirement of juvenile Atlantic salmon, Salmon salar L. Triplicate groups of fish (mean initial weight 1.4 g) were fed semipurified, casein-gelatine-based diets containing one of five levels of P (4, 8, 10, 15 and 25 g kg⁻¹) from Ca(H₂PO₄)₂·H₂O, or a commercial feed (17 g kg⁻¹ P) for 9 weeks. Weight gains did not differ significantly among treatment groups fed the experimental diets but were slightly less than gains in fish fed the commercial feed. Feed efficiency (wet weight gain/dry feed consumed) was similar in all groups, averaging 1.45. Availability of dietary P, estimated from apparent retention and apparent digestibility, was 86%. Whole-body P concentrations declined in fish fed diets containing less than 10 g kg⁻¹ P. Fitting a logistic curve to dietary P vs. whole-body P concentrations indicated that a minimum of 11 g kg⁻¹ dietary P (9 g kg⁻¹ digestible P) was required by juvenile Atlantic salmon to maintain whole-body P concentrations at initial levels. Calculation of a dietary requirement using a simple factorial model which incorporated measurements of P availability, feed efficiency and normal whole-body P concentration indicated that the dietary requirement was approximately 10 g kg⁻¹. The dietary requirement established in this study (10–11 g kg⁻¹) is higher than previously reported for Atlantic salmon or other fishes. Possible reasons for the wide range of reported dietary P requirements in fishes are discussed.     

Vertebral column deformity with curved cross-stitch vertebrae in Norwegian seawater-farmed Atlantic salmon,Salmo salar L.

Pathological changes in the vertebral column of farmed Atlantic salmon in Norway have been reported since the 1990s. Based on the characteristic radiographic findings, we here present a vertebral column deformity named “curved cross-stitch vertebrae” that mainly affects the middle aspect of the vertebral column. Sixty fish, from the west/northwest coast of mid-Norway, were sampled at slaughter and examined by radiography, computed tomography (CT), necropsy, macrophotography, and histology. The vertebral deformities were radiographically graded as mild, moderate, or marked. The main differences between these grades of changes were defined by increased curving of the peripheries of endplates, reduced intervertebral spaces, and vertical displacement of the vertebrae. The curved rims of endplates were located peripheral to a continuous and approximately circular borderline. The CT studies revealed small, multifocal, hypo-attenuating, round to crescent-shaped areas in the notochord, compatible with the presence of gas. Additionally, histology revealed that the axial parts of endplates had circular zones with perforations, through which either notochordal tissue prolapsed into the vertebrae or vascularized fibrochondroid proliferations extended from the vertebrae into the notochord. Inflammation was present in many vertebral bodies. To the best of our knowledge, this is the first report of gas in the notochord of fish.     

Increased dietary phosphorous prevents vertebral deformities in triploid Atlantic salmon (Salmo salar L.)

Triplicate groups of triploid and diploid Atlantic salmon were fed diets with a low (LP, total P: 7.1 g kg^?1), medium (MP, total P: 9.4 g kg^?1) or high (HP, total P: 16.3 g kg^?1) phosphorous (P) level from first feeding (0.18 g) to transfer to sea water (~50 g, duration: 203 days) and subsequently fed a commercial diet in sea water for 426 days (~3 kg). This study examined the short‐ and long‐term effects of dietary P on freshwater performance (mortality, growth), vertebral deformities (radiology), bone cell activity (ALP and TRACP enzyme activity in vertebrae and scales, and fgf23, bgp and igf‐I relative gene expression in vertebrae), bone mineralization (ash content) and some parameters related to fish condition (heart and liver size). Irrespective of ploidy, at seawater transfer, fish fed the MP diet had significantly highest length and weight and those fed the LP diet significantly lowest length and weight, while those fed the HP diet had intermediate lengths and weights. Increased dietary phosphorus reduced deformities in both ploidies at seawater transfer; however, triploids fed the LP and MP diets had more deformities than diploids fed the respective diets, while there was no ploidy effect observed for fish fed the HP diet. The vertebral bone ash content at seawater transfer was significantly higher in diploids than in triploids when fed the MP diet only. Alkaline phosphatase (ALP) and tartrate‐resistant acid phosphatase (TRACP) enzyme activities and relative gene expression of bone hormones involved in metabolism of plasma phosphate (fgf23) and bone growth (bgp) were not affected by ploidy at seawater transfer, but by dietary P level; LP increased ALP activity and reduced TRACP activity and fgf23 and bgp expression levels in vertebral bone. In scales, LP increased both ALP and TRACP activity. At the termination of the seawater period, the group‐wise pattern in occurrence of vertebral deformities was the same as at seawater transfer. The present results on mortality, growth, bone mineralization and development of skeletal deformities all demonstrate that triploids have a higher P requirement than diploids in fresh water. This study shows that an optimalization of P nutrition for triploid Atlantic salmon can improve health and welfare and reduce down‐grading of triploid salmon.     

The need for riboflavin supplementation in high and low energy diets for Atlantic salmon Salmo salar L. parr

A two-factor study was conducted to evaluate the effects of dietary riboflavin and lipid levels on the growth, health performance and riboflavin status of Atlantic salmon ( Salmo salar ). Atlantic salmon parr were fed four fishmeal-based diets with or without supplementation of 20 mg riboflavin kg^–1, at two lipid levels, 150 or 300 g kg^–1. Each diet was fed to triplicate tanks of fish for 12 weeks. Unsupplemented diets contained between 6 and 8 mg riboflavin kg^–1. There were no significant differences in growth as a result of riboflavin supplementation. No mortality or histomorphological changes in eye tissues were observed. Dietary treatments did not affect blood haemoglobin values. After 12 weeks, muscle lipid content seemed to be reduced by riboflavin supplementation irrespective of dietary lipid level. Riboflavin status of whole body, muscle, liver, kidney and eye lenses is reported. Saturation levels of riboflavin in liver and muscle were reached with unsupplemented diets. The concentrations of riboflavin and lipid in liver were negatively correlated. There was a tendency of higher whole body riboflavin concentration in fish fed high-lipid diets. Based on growth, absence of deficiency signs and maximal tissue saturation of riboflavin, it can be concluded that the requirement for riboflavin was met by the natural riboflavin content in the raw materials of the feed. However, independent of dietary lipid level, dietary riboflavin supplementation may increase lipid utilization in rapidly growing salmon parr.     

Control of phosphorus homeostasis of Atlantic salmon (Salmo salar) in fresh water

Studies were conducted to determine the absorption, excretion and requirement of dietary phosphorus (P) by Atlantic salmon (Salmo salar). Triplicate groups of salmon parr, initial weight 15 ± 0.5±g , were fed, diets containing 4, 5, 6, 7, 8, 9, 11 and 13 mg P and 20 KJ of digestible energy (DE) per±g of diet (dry matter basis, DMB) to satiation for 16 weeks. The basal diet containing 4 mg P g^-1 (0.15 mg available P per KJ DE) was supplemented with graded levels of calcium phosphate, Ca(H₂PO₄)²H₂O to formulate the eight experimental diets. The fish were reared in fresh water at a temperature of 15 °C on a 12 h photoperiod. Vertebrae ash increased from 316 to 516 mg g^-1 fat-free dry matter with an increase in dietary P content. P requirement was estimated by using a four-parameter sigmoidal equation. The data suggests that a diet of 0.28 mg available P per KJ DE is needed for Atlantic salmon. Phosphate and calcium levels in plasma and bone increased, whereas levels of magnesium and liver cholecalciferol decreased, with an increase in dietary P.Phosphate excretion in urine and apparent availability of P were determined in deficient and replete fish. In deficient fish, the urine phosphate concentration was 0.10 mmol L^-1 before feeding and 0.25 mmol l^-1 after feeding, whereas in replete fish these concentrations were 1.09 and 5.11 mmol l^-1, respectively. The increase in urine phosphate concentration was higher in replete fish than in deficient fish, however, the apparent absorption of P was found to be significantly lower in replete fish than in deficient fish. These results suggest that similarly to terrestrial vertebrates, P homeostasis in Atlantic salmon is controlled by absorption in the intestine, conservation in the kidney and storage in the bones.     

Variation in commercial sources of soybean meal influences the severity of enteritis in Atlantic salmon (Salmo salar L.)

Soybean meal (SBM) is a potential alternative for the replacement of fishmeal in aquafeeds. In Atlantic salmon, however, dietary SBM causes an inflammation of the distal intestine, known as SBM-induced enteritis. The objective of the present study is to verify whether different (geographically spread) commercial sources of SBM yield contrasting inflammatory responses. To do so, six SBM batches from different origins were included in the Atlantic salmon diets at the level of 20%. After 4 weeks of feeding, the distal intestine of the salmon was sampled and scored by a semi-quantitative scoring system, which assessed six separated parameters, characterizing the extent of enteritis. The overall mean score as well as the score of the separate parameters varied between the different commercial sources of SBM included in the diet. The variation in SBM caused different degrees of disparity in the score of the separate parameters. The parameter that was most affected by the variation in the source of SBM was the disappearance of supranuclear vacuoles in enterocytes. In contrast, the increase in goblet cells showed the smallest variation between the different SBM sources. This study shows that different commercial sources of SBM can result in differences in the severity of SBM-induced enteritis in Atlantic salmon.     

An estimation of dietary iron requirement of Atlantic salmon, Salmo salar L., parr

A study was conducted to determine the dietary iron requirement of fingerling Atlantic salmon Salmo salar L. During the first 4 weeks of the experiment, fish with an initial weight of 5 g were fed a casein–gelatine-based purified diet which contained 11 mg iron kg^?1. Thereafter duplicate tanks (200 fish in each) were fed the casein–gelatine purified diets containing supplemental iron levels of 0, 10, 20, 30, 40, 60, 100, 200 or 400 mg iron kg^?1 (added as FeSO_?4* 7H₂O) for 12 weeks. Weight gain, body length and mortality were monitored. Liver iron and ascorbic acid concentration were analysed in addition to whole-body iron, manganese and zinc concentration. Several haematological parameters were also measured. There were no significant differences in weight gain and survival of salmon fed diets containing different iron levels. Haematological values, hepatic and whole-body iron concentrations were, however, significantly affected by the dietary iron content. Liver vitamin C concentration decreased with increasing dietary iron levels. Dietary supplementation with iron significantly reduced whole-body manganese, but no effect of dietary iron on whole-body zinc was found. Based on haematology and hepatic iron concentration, the iron requirement of Atlantic salmon was determined to be between 60 and 100 mg iron kg¹.     

Water temperature regimes affect cataract development in smolting Atlantic salmon, Salmo salar L.

The effect of fluctuation in water temperature during the freshwater rearing stage on cataract development in Atlantic salmon was investigated. Presmolts were exposed to either constant low or high temperatures, or high temperature with cold-water fluctuations. Temperature fluctuations caused the fastest growth rate and most severe cataracts, whilst low temperature resulted in slow growth and minor cataracts. The fish were then individually marked and maintained together in a seawater net pen for 7 months. Cataract progressed in all groups, fish from the low temperature group showed the fastest subsequent growth, and developed cataracts to the same degree as fish from the other groups. There were no statistically significant differences in selenium-dependent glutathione peroxidase levels in pooled samples of aqueous humour, lens and plasma from fish with or without cataract, except from the last freshwater samples, where cataractous fish showed lower plasma activity. Plasma cortisol and glucose levels did not differ, nor did whole eye riboflavin levels. Higher concentrations of some free amino acids in whole eyes were found in fish with cataract. This study shows that fluctuation in water temperature may cause both increased growth rate and cataract development in Atlantic salmon and that cataract development initiated in the freshwater rearing phase continues after transfers to seawater.     

The effect of dietary vitamin A on the immunocompetence of Atlantic salmon (Salmo salar L.)

Atlantic salmon, Salmo salar L. were maintained on diets containing low (0.37 mg kg^–1 diet), normal (1.95 mg kg^–1 diet) and high (15 mg kg^–1 diet) levels of vitamin A fed at 1.5% body weight per day. After 4 months, liver vitamin A levels reflected dietary intake and growth rates of all three groups were similar. Kidney leucocyte migration and serum bactericidal activity were found to be significantly reduced in fish fed low levels of vitamin A. On the other hand, high levels of vitamin A in the diet were found to augment serum antiprotease activity relative to the levels found in the other dietary groups. However, phagocyte respiratory burst activity, bactericidal activity and eicosanoid production were unaffected by the dietary vitamin A regime, as were lymphocyte functions (lymphokine and antibody production) and both serum lysozyme and classical complement activity. That the overall immunomodulatory effect of vitamin A was small was reflected in the resistance to Aeromonas salmonicida. No significant differences were found between the different vitamin A intake groups despite a trend to decreased resistance in the low vitamin A diet group.     

Supplementation of dietary minerals during the early seawater phase increase vertebral strength and reduce the prevalence of vertebral deformities in fast-growing under-yearling Atlantic salmon (Salmo salar L.) smolt

An earlier study demonstrated that under‐yearling (0+) Atlantic salmon (Salmo salar L.) smolt had a lower vertebral mineral content and mechanical strength and higher prevalence of vertebral deformities than 1+ smolt during the early seawater (SW) phase. The present study aimed to examine if commercial extruded high‐energy diets need to be supplemented additional minerals for proper bone mineralization and prevention of bone deformities in fast growing 0 + smolts. We studied vertebral morphology with radiology, and bone mineral content and mechanical strength in 60 g 0+ smolt fed diets with a normal (NM) or elevated (HM) bone mineral (P and Ca) contents from SW transfer (week 0) until 10 times weight increase at week 17. Thereafter, both groups were fed a commercial diet until a mean slaughter weight of 4100 g after 57 week. There were no differences in body weight and length between the dietary groups during the study, while the condition factor differed significantly at the final sampling (NM 1.40; HM 1.29). The most common bone deformity observed was compressions in the tail region of the vertebral column. Lower incidences of vertebral deformities (percent individuals with one or more deformed vertebrae) was observed in the HM group in week 17 (HM 20%; NM 47%) and week 57 (HM 37%; NM 73%), also reflected by higher vertebral length/dorso‐ventral diameter ratio in weeks 17 (HM 0.99; MN 0.92) and 57 (HM 0.97; NM 0.88). The HM group had significantly higher vertebral mineral content (HM 550 g kg^?1; NM 480 g kg^?1) and mechanical strength (HM 9050 g mm^?1; NM 4600 g mm^?1) than the NM group after 8 week feeding. Plasma levels of Ca, P and D‐vitamin metabolites recorded in week 8 reflected changes in P homeostasis, but could not explain the preventive effect of the HM diet on development of bone deformities. The results suggest that elevated dietary mineral content during the early SW phase may reduce the prevalence of vertebral deformities in fast growing 0 + salmon smolts.     

Magnesium requirement of Atlantic salmon (Salmo salar L.) parr in seawater-treated fresh water1

This experiment was undertaken to establish the magnesium (Mg) requirement in young Atlantic salmon, Salmo salar L., in seawater-treated fresh water. In Norwegian hatcheries it is a common practice to add sodium hydroxide and/or sea water (1–2%) to improve pH and conductivity of the natural fresh water. Parr with initial weight of 8 g, were divided in six triplicate groups in brackish water containing 54 mg Mg L^?1 and fed a basal casein-gelatine diet supplemented with minor amounts of krill and fish meal (containing 200 mg Mg kg^?1) for an initial period of 3 weeks. Thereafter the fish were fed this diet supplemented with either 0, 100, 200, 300, 400 or 500 mg Mg kg^?1 (as MgSO₄) for 12 weeks. Growth and feed efficiency were recorded. Concentrations of Mg and other divalent cations (Ca and Zn) were measured in whole fish, serum and vertebrae. Sodium concentration in vertebrae was also measured. Growth and feed efficiency were unaffected by the levels of dietary magnesium used in the experiment. Magnesium concentrations in the whole body, serum and vertebrae Mg appeared to be more sensitive than growth and feed efficiency to differences in dietary Mg intake. The group fed the unsupplemented diet showed significantly lower Mg concentration in these tissues than the other groups. Whole-body calcium concentration was negatively correlated with dietary Mg and Ca:Mg ratios in the vertebrae were significantly affected by the dietary Mg levels. Zinc concentration in whole body, serum and vertebrae was not altered by the dietary Mg levels. Further, vertebral Na concentration did not vary between the dietary treatments. In conclusion, a minimum Mg supplementation level of 100 mg kg^?1 dry diet (in total, 326 mg kg^?1) was needed to maintain Mg concentration in the whole body and serum and for proper bone mineralization.     

Teratogenicity of elevated egg incubation temperature and egg vitamin A status in Atlantic salmon, Salmo salar L

The present study was undertaken to investigate the possibility that high egg vitamin A (VA) status in combination with elevated egg incubation temperatures may cause deformities in Atlantic salmon, Salmo salar L. Egg batches selected for their total VA concentration were exposed to low (normal, 8 degrees C) or elevated (14 degrees C) egg incubation temperatures. Temperature was the main factor causing bone deformities such as warped gill opercula, fin and jaw deformities, but not for the development of spinal deformities where all groups displayed a 'baseline' occurrence of mild deformity (decreased vertebral size in the cephalic region) and no systematic variation in the occurrence of serious spinal deformities (fused vertebrae). A possible effect of egg incubation temperature fluctuation was found for the groups reared at low temperatures. An indication of a negative effect of elevated egg VA status for the development of organ deformities such as missing septum transversum and situs inversus was found in addition to temperature effects, however, no firm conclusions could be drawn from the present data. The phenotypes for temperature-induced deformities resembled the phenotype of VA-induced deformities, but no clear conclusions on the causality of the deformities found in the present study could be drawn. Egg incubation temperatures, both absolute temperature and temperature variations, should therefore be strictly controlled.     

Biotin in practical fish-meal based diet for Atlantic salmon Salmo salar L. fry

Groups of Atlantic salmon fry (0.19 g initial weight) were fed a fish-meal based starter diet with different supplements of biotin (0, 0.5, 1.0 and 1.5 mg biotin kg^–1) in triplicate tanks for 18 weeks. The basal diet contained 0.3 mg total biotin kg^–1. The experimental design included a negative control diet made by replacing 10% of the fish-meal with spray-dried raw hen's egg white.
Throughout the experimental period the fish grew to about 5 g and there were no significant differences in growth and mortality among the groups of fish fed the fish-meal diets. At the end of the experiment there were no significant differences in biotin level in the liver, while whole-body biotin concentrations correlated significantly with the dietary biotin concentrations. No significant increase in pyruvate carboxylase (PC) activity was found in livers from fish given different dietary levels of biotin. The control diet with egg white resulted in severe growth reduction and increased mortality compared with the other dietary groups. The concentrations of biotin in liver and whole body were decreased in fish fed egg white. Increased levels of glycogen and reduced PC activity in the liver were observed in this group after 18 weeks.
Histology of the gills showed no differences in appearance when fish were fed fish-meal based diets while the addition of egg white resulted in hypertrophy and hyperplasia of the gill tissue and extensive fusions of the secondary gill lamellae.
The results show that there is no need for supplemental biotin in practical fish-meal based diets for Atlantic salmon fry to achieve optimal growth, survival and maximal liver PC activity.     

Influence of long term ammonia exposure on Atlantic salmon (Salmo salar L.) parr growth and welfare

The objective of this study was to determine the long‐term effects of ambient unionized ammonia nitrogen (NH₃‐N) combined with different feeding regimes on Atlantic salmon Salmo salar L parr growth, welfare and smoltification. Previous studies on the parr stage of Atlantic salmon have mostly focused on acute exposure, or at low temperatures. Atlantic salmon parr were exposed for 105 days (at 12°C, pH 6.8) to four sublethal ammonia concentrations ranging from 0.1 to 35 μg L^?1 NH₃‐N (0.1–25 mg L^?1 TAN) at two feeding levels: full feed strength (+20% overfeeding) and 1/3 of full feed strength. After 21 days, it was observed that 32 μg L^?1 NH₃‐N reduced growth rate of parr fed full ration, but this effect was not evident at the end of the exposure. Feed utilization was not affected by ammonia exposure at any sampling point. Increasing ammonia levels were associated with a higher prevalence and severity of gill damage at 22 days but not at the end of the exposure. The examination of welfare indicators revealed only a few pathologies, not related to ammonia exposure. In addition, higher ammonia concentrations did not appear to influence the development of hypo‐osmoregulatory ability during parr‐smolt transformation.     

Effect of dietary lipid level on muscle composition in Atlantic salmon Salmo salar

This study was conducted to determine the effects of feeding increasing lipid concentrations (310, 380 and 470 g kg^–1 lipid on dry weight) in diets based mainly on herring byproducts to Atlantic salmon Salmo salar . The diets were isonitrogenous, varying in dietary lipid content at the expense dietary starch. Average fish weight increased from 1.2 kg in April to 2.2–2.7 kg at the end of the feeding trial in September. Significantly greater growth was found in fish fed either the 380 g kg⁻¹ or the 470 g kg⁻¹ lipid diets compared with the 310 g kg⁻¹ lipid diet. Muscle lipid content increased in all dietary groups on a wet weight basis from 7.7 ± 1.4% to 12 ± 3% in salmon fed the 310 g kg⁻¹ lipid diet, and to 16 ± 2% in salmon fed the 380 g kg⁻¹ and 470 g kg⁻¹ lipid diets. In fish of similar weight there was a positive correlation between dietary lipid and muscle lipid concentrations. Low concentrations of muscle glycogen were detected in fish fed each of the diets, while muscle vitamin E concentrations slowly decreased as muscle lipid increased. Muscle fatty acid composition reflected dietary fatty acid profiles, containing similar percentages of total saturated, monoenic and n-3 fatty acids (20:5n-3 and 22:6n-3) in fish from all dietary treatment groups. However, a higher ratio of n-3/n-6 was found in muscle from fish fed the 470 g kg⁻¹ lipid diet compared with the other two groups. Blood chemistry values varied somewhat, but all values were within normal ranges for Atlantic salmon of these sizes.