Rapid and non-invasive measurements of fat and pigment concentrations in live and slaughtered Atlantic salmon (Salmo salar L.)

The aim of this study was to non-invasively determine fat and pigment concentrations in salmon muscle based on visible and near infrared (VIS/NIR) spectroscopy measurements of live/whole fish and fillets, and by means of digital photography (DP) of fillets. The fish used were two populations of farmed Atlantic salmon (Salmo salar L.) consisting of 46 salmon averaging 0.7 kg (range 0.17–1.7 kg, Group S) and 30 salmon averaging 2.3 kg (range 1.4–4.1 kg, Group L). Chemical analyses (fat and pigment content) and computerized tomography, CT (fat content) were used as reference methods. Group L was analysed in the live state (VIS/NIR), after gutting (VIS/NIR and CT), and as fillets (VIS/NIR and DP). Group S was analysed in the gutted state (VIS/NIR) and as fillets (VIS/NIR and DP). VIS spectroscopy predictions of pigment in whole salmon from Group S were obtained with a root mean square error of prediction (RMSEP) of 0.9 mg kg^− 1 astaxanthin, and a correlation between VIS spectroscopy predicted and chemically measured pigment of r = 0.85 (p < 0.0001). The fat concentration was determined by the NIR spectroscopy in live fish with RMSEP = 1.0 fat% unit, and a correlation with chemical reference values of r = 0.94 (p < 0.0001). Fat predictions from NIR spectroscopy correlated also well with predictions from CT analyses, r = 0.95 (p < 0.0001). VIS spectroscopy and DP were equally well suited to determine pigment concentrations in salmon fillets, with prediction errors of only 0.4 mg kg^− 1 astaxanthin, and a correlation with chemically determined pigment of r = 0.92 (p < 0.0001). The results obtained in the present study are the first to demonstrate successful non-invasive pigment predictions in whole salmon using VIS/NIR spectroscopy, and the possibility for simultaneous, rapid and non-destructive quantification of fat and pigment concentrations.     

红鳍东方鲀死后僵直及生化变化特性

以养殖红鳍东方鲀为研究对象,活体速杀放血去内脏,设冰藏组和室温组进行6 d对照贮藏。贮藏期间观察记录鱼体死后僵直状态并监测僵直指数,跟踪分析肌肉生化变化,生化指标包括ATP及关联物、糖原、pH以及肌肉蛋白磷酸化等。结果显示,冰藏组在死后7 h左右才开始发生僵直,僵直指数最大可达89%,并可维持20～24 h;冰藏至第4天,僵直指数仍可分别保持在9%和16%。室温对照组中没有明显观察到僵直发生发展过程,虽然测出最大僵直指数为71%,但僵直现象转瞬即逝。死后贮藏过程中糖原水平迅速下降,室温对照组贮藏至第3天几乎消耗完全,而冰藏组消耗殆尽发生在5 d以后;肌肉pH分析结果与糖原变化趋势相似,冰藏组的pH值较室温对照组下降的慢,且高于室温对照组。速杀后至僵直开始,各处理组ATP均迅速消耗,IMP快速积累且为主要核苷酸降解产物;冰藏组IMP在第3天左右达到最大值9.5μmol/g,随后开始呈下降趋势,贮藏到第6天时IMP仍保持在7.5μmol/g左右,始终处于较高水平。室温对照组则为IMP在第1天达到最大值9.2μmol/g后迅速下降,Hx积累量明显增多。蛋白质磷酸化结果表明,鱼体死后的僵直状态...     

Temporal changes in texture, gaping, composition and copper status of Atlantic salmon (Salmo salar, L) fed moist feed or extruded dry feed

Temporal development in product quality and copper status was investigated in Atlantic salmon (initial weight 2.3 kg) fed alginate-based moist feed (MF) or commercial extruded dry feed (DF). The fieldwork was conducted from January to May in sea-cages (800 m³) off the Norwegian west coast. The dry matter content (DM) in the muscle of the MF group was stable at about 32% throughout the experiment, while the DM of DF group increased linearly from 32% to 35%. Salmon were sampled for analyses of Cu status, fillet gaping, texture and pH in March and April. The serum Cu content of the MF group was highest in March, but no significant effect of dietary treatment was observed on Cu status of muscle or liver. The Cu level in serum and muscle decreased from March to April in both fish groups, but the hepatic Cu level showed no temporal changes. Gaping incidence and pH were higher in the MF group in April compared with the DF group and, for both fish groups, fillet gaping was higher and hardness was lower in April than in March. Variation in serum Cu level explained 32% of the variation in fillet hardness, and serum and muscle Cu level related negatively with gaping. At the end of the experiment the condition factor, and fillet and visceral fat contents were higher in the DF group, while sensory evaluated hardness and tastiness were similar for both dietary treatments. In conclusion, sampling time had a greater impact on Cu status, texture and gaping than dietary treatment during springtime in adult Atlantic salmon. Dietary treatment significantly affected body shape, and fat and dry matter contents.     

Growth of Atlantic salmon (Salmo salar L.) in a variable diel temperature regime

In five experiments, Atlantic salmon (Salmo salar L.) parr were found to grow better under conditions of rhythmically alternating water temperature (P<0.031), than control groups reared under stable temperature conditions. The daily temperature sums for the experimental and the control groups were carefully equalized and monitored in all five experiments. The experimental group was reared in a rhythmically alternating temperature regime, of 10.0 h of high temperature (16.0°C) and 10.0 h of low temperature (10.0°C), the temperature adjustments being made during the 2 h between the periods of fixed temperature. The control group were reared in a relatively stable temperature regime (13.00–13.98°C). The growth rate of the fish reared under the varying temperature conditions was higher (mean for all five experiments 1.96% day⁻¹) than that for the salmon reared under stable conditions (1.85% day⁻¹).     

Anisakid larva in the viscera of a farmed Atlantic salmon (Salmo salar)

Parasitic nematodes of the family Anisakidae occur in the visceral cavity and surrounding tissues of many marine fish species at a prevalence as high as 100% in wild salmon samples. Human consumption of fish products containing these parasites can result in the zoonotic disease anisakiasis, and Anisakis simplex is most commonly associated with human disease. Previous studies of farmed salmon have found no anisakids in viscera or muscle, presumably because formulated feed production renders parasite larvae nonviable. However, among farmed Atlantic salmon (Salmo salar) examined by histopathology as part of a provincial government auditing program in British Columbia, Canada, 1 of 894 (0.11%) had an anisakid larva partly embedded in the wall of an intestinal cecum. Skeletal muscle is not examined as part of the government's program, but other studies have correlated anisakids in the viscera and muscle. Using anisakid prevalence in viscera as an estimate of its prevalence in muscle, the risk ratio of anisakid parasites in commercial product is 570 times less in farmed than in wild Atlantic salmon.     

Furunculosis in Atlantic salmon (Salmo salar L.) is not readily controllable by bacteriophage therapy

The potential of bacteriophage therapy to control bacterial disease in farmed fish was tested using, as an example, furunculosis of Atlantic salmon, caused by Aeromonas salmonicida subsp. salmonicida.

In vivo testing with Atlantic salmon and rainbow trout (Oncorhynchus mykiss Walbaum) showed no adverse effects, with bacteriophage generally cleared within 96 h of administration by either intraperitoneal (i.p.) injection or oral in-feed.

Juvenile Atlantic salmon were administered a combination of bacteriophage O, R and B (1.9 × 10⁸ pfu fish^− 1) by i.p. injection, after they had been challenged with A. salmonicida subsp. salmonicida 78027, also by i.p. injection. The fish that were injected with bacteriophage immediately after challenge died at a significantly slower rate then those that were either not treated with bacteriophage, or treated 24 h post-challenge. However, the end result (100% mortality) was not affected.

In further experiments the effects of oral (1.88 × 10⁵ pfu g^− 1 fish^− 1 daily for 30 days), bath (1.04 × 10⁵ ml^− 1 daily for 30 days) and i.p. (6.25 × 10⁷ pfu fish^− 1) phage treatment to control furunculosis in experimentally infected Atlantic salmon were compared with antibiotherapy (treatment with 10 mg kg^− 1 bw^− 1 day^− 1 oxolinic acid for 10 days), using an indirect cohabitation challenge. No protection was offered by any of the bacteriophage treatments, compared to the positive challenge group, although significant protection was offered by the oxolinic acid treatment. Analysis of samples taken from the trials demonstrated that bacteriophage were correctly administered to the fish and, on occasion, were isolated from fish that had succumbed to furunculosis. It was also shown that bacteriophage resistant A. salmonicida subsp. salmonicida isolates could be recovered from mortalities in all the treatment groups.

The results suggest that, although there were no safety problems associated with the approach, furunculosis in Atlantic salmon is not readily controllable by application of bacteriophage.     

The mineral content affects vertebral morphology in underyearling smolt of Atlantic salmon (Salmo salar L.)

This study investigated the individual variation in vertebral morphology and mineral content (as % of bone dry weight) in rapid growing underyearling smolt (n = 33) twelve weeks after transfer to seawater. The smolt, which were reared in triplicate tanks, had a large individual variation in vertebral bone mineral content (Tank A: 36.2% min, 45.2% max, 39.6% mean. Tank B: 32.6% min, 46.6% max, 40.0% mean. Tank C: 38.5% min, 47.9% max, 42.4% mean), and were subdivided into two groups based on mean within each tank: high mineral content (HMC, above tank mean, n = 15) and low mineral content (LMC, below tank mean, n = 18). Vertebrae of smolt with a low mineral content were more compressed in the anterior–posterior direction (HMC vertebral length/dorso-ventral diameter ratio 0.83, LMC 0.80). This was related to a change in the growth direction of the vertebral cone. This change occurred around transfer to seawater and was characterised by an increased angle between the wall of the cone of the vertebrae and the cranial–caudal axis, and gave the vertebrae a compressed appearance. Smolt with a high mineral content were significantly longer (HMC 28.1 cm, LMC 26.5 cm) and heavier (HMC 270 g, LMC 210 g) twelve weeks after transfer to seawater.     

Lipid absorption in different segments of the gastrointestinal tract of Atlantic salmon (Salmo salar L.)

Gastrointestinal lipid absorption in Atlantic salmon was studied following force-feeding with a standard grower diet to which isotope-labelled free fatty acid (FFA) [1-¹⁴C]-decanoic acid (¹⁴C-10:0) and triacylglycerol (TAG) [9,10-³H(N)]-triolein (trioleic acid; ³H-18:1) were added. Following force-feeding, the 15 fish, with an average weight of 704 g, were kept in five circular tanks, three fish per tank, supplied with seawater (salinity, 32 g l⁻¹). At 3, 6, 12, 18 and 48 h, the fish from one tank were killed, and the gastrointestinal (GI) tract was removed and divided into six segments: stomach (ST), anterior, mid, and distal pyloric ceca (PCA, PCM, and PCD, respectively), mid intestine (MI), and distal intestine (DI). The levels of radioactivity (dpm [disintegrations per minute] μg⁻¹ tissue) from the ¹⁴C-10:0 and the ³H-18:1 substrates were measured in tissue samples from each segment, allowing an estimation of the amounts of fatty acid substrates absorbed from the lumen into the intestinal cells. The highest levels of radioactivity from both fatty acid substrates were measured in tissue from pyloric ceca (PC) 12 to 18 h after force-feeding. The level of radioactivity from the ¹⁴C-10:0 substrate was significantly higher in the PCA than in the PCM and PCD, while there was no clear difference in the level of radioactivity from the ³H-18:1 substrate measured among the different PC tissue segments and the level measured in MI. The level of radioactivity in tissue from DI was negligible to low for both fatty acid substrates. Total lipid accumulation in tissue from PCM, MI and DI was quantified morphometrically at each sampling point using light microscopy and image analysis. These results confirmed the findings from the isotope study, where the highest levels of fat were present at 12 and 18 h following force-feeding. In conclusion, PC was the most important site for fatty acid absorption in the GI tract of Atlantic salmon.     

Microsatellite genetic variation between and within farmed and wild Atlantic salmon (Salmo salar) populations

Genetic diversity between three farmed and four wild populations of Atlantic salmon from Ireland and Norway were analysed using 15 microsatellite markers. High levels of polymorphism were observed over all populations with the average number of alleles and average heterozygosity at 17.8 and 0.70, respectively. Farmed salmon showed less genetic variability than wild salmon in terms of allelic diversity but not necessarily in terms of overall heterozygosity. Between farmed populations significant differences were observed in expected heterozygosity suggesting that more intensive breeding practices may have resulted in a further erosion of genetic variability. Phylogenetic analysis using either populations or individuals as nodes show a clustering of populations into two groups, farmed and wild. This suggests that founder effects and subsequent selection have had more effect on the genetic differentiation between these strains than geographical separation. This technology has great potential for use in aquaculture situation where levels of genetic variation could be monitored and inbreeding controlled in a commercial breeding progra.     

The effect of slaughtering procedures on blood spotting in rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar)

Rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) were submitted for various slaughter and bleeding procedures to see what effect this would have on blood drainage of the muscles. Results show that the bleeding method is of less importance, while it is the timing that is important. No significant difference in bloodspotting was observed between fish that were bled live by a gill cut or percussive killed and bled by gutting. Most of the drainage of blood in the fish muscle seems to occur within the first hours postmortem, so rigor mortis is of little importance. The visual appearance of the fillet was influenced by number and size of the bloodstains. Colour measurements with Hunter L*, a*, b* did not reveal this. We conclude that a gill cut is not necessarily to obtain bleeding, so the industry can omit this phase and go directly to gutting.     

A radiological study on the development of vertebral deformities in cultured Atlantic salmon (Salmo salar L.)

This study investigated the development of skeletal deformities in individually tagged Atlantic salmon (n = 805) from the parr stage (Sept 2001, 70 g mean ± 34 g S.D.) until 10 month after transfer to seawater (Feb 2003, 3040 g mean ± 1097 g S.D.). A subgroup of the total population (n = 129) was radiographed as parr (Feb 2002) and again 10 months after transfer to seawater (Feb 2003). Eight percent of the males matured sexually during their first autumn in sea (jack), and were excluded from further analysis. Based on an external examination of each fish (n = 773), 1.8% (n = 14) developed skeletal deformities (0.1% operculum deformities (n = 1), 0.4% jaw deformities (n = 3), 1.3% vertebral deformities (n = 10)) during the experiment. Based on evaluation of radiographs (n = 129), the prevalence of vertebral deformities was 7.0% (n = 9) at the parr stage, and 12.4% (n = 16) 10 months after transfer to seawater. From radiographs, longitudinally compressed vertebral bodies without intervertebral spaces were classified as ankylosis and compression, longitudinally compressed vertebral bodies with intervertebral spaces were classified as compressions, and dislocated vertebral bodies with a normal morphology and without intervertebral spaces were classified as ankylosis and dislocation. Of the fish that developed deformities during the experiment, 8 had ankylosis and compressions, 7 had compressions and 1 had ankylosis and dislocation. Ankylosis and compression developed in the region between vertebrae number 1 and 16, whereas compressions developed in the region between vertebrae number 13 and 49. Most of the individuals with compression 10 months after transfer to seawater had normal vertebral columns as parr, whereas all individuals with compression and ankylosis 10 months after transfer to seawater had deformed vertebral columns as parr.     

Seawater adaptation and growth of post-smolt Atlantic salmon (Salmo salar) of wild and farmed strains

Atlantic salmon smolts (Salmo salar L.) of wild (Namsen) and farmed (AquaGen) strains were transferred to full-strength seawater (33‰) for 0 (initial control group), 0.5, 1, 2, 4, 8, 14, 30, 42 and 60 days at three different temperatures (4.3, 9.4 and 14.3 °C). Freshwater temperature in each tank was adjusted to test conditions 10 days prior to transfer. Physiological adaptation was monitored as changes in plasma growth hormone levels, gill Na⁺,K⁺-ATPase activity, plasma chloride levels and survival in seawater. Overall, smolts from the wild strain were better able to tolerate transfer to seawater than smolts from the hatchery strain. A delay in the osmotic disturbance and a prolonged period of osmotic stress were observed at the low temperature. Circulating GH levels increased transiently in all groups during the first 12–48 h in seawater and long-term GH levels were positively correlated with seawater temperature. Growth rates were influenced by temperature and strain, with the farmed smolts showing a higher growth than the wild smolts. Food Conversion Efficiency (FCE) was higher in smolts from the farmed strain, whereas no differences in daily food consumption were observed. Optimum temperature for FCE was calculated to be 10.5 °C, whereas the optimal temperature for growth in seawater was calculated to be 13.0 °C. We suggest that the observed differences in seawater tolerance, growth and food conversion probably are genetic and may reflect the fact that the hatchery fish have been bred for rapid growth for several generations.     

Long-term separate and combined effects of environmental hypercapnia and hyperoxia in Atlantic salmon (Salmo salar L.) smolts

Atlantic salmon (Salmo salar L.) parr (mean start weight 50 g) were reared in freshwater (FW) and exposed to three levels of oxygen saturation measured in effluent water; control group (93% O₂, LO₂), medium (111% O₂, MO₂) and high (123% O₂, HO₂). Further three groups were exposed to similar water oxygen levels in combination with elevated carbon dioxide levels (17–18 mg L^– 1 CO₂), named LO₂–CO₂, MO₂–CO₂ and HO₂–CO₂, respectively. The experiment was run in duplicate tanks for 42 days, and the fish were subsequently transferred to the same seawater (SW) regime for 45 days for an assessment of post-smolt growth. As a consequence of the CO₂ addition, tank pH levels in the FW period were reduced from 6.7 to 5.9 for the hypercapnia groups compared to for the normcapnia groups. Water temperature in FW ranged between 6.4 and 9.0 °C. Citrate was added to the water to complex labile aluminium.In the CO₂ groups observed ventilation frequencies were significantly increased compared to the control (p < 0.05). This difference declined towards the end of the FW period, suggesting acclimation to elevated CO₂. The degree of oxygenation appeared to contribute to the acclimation as the lowest mean ventilation frequency on day 36 was found in the HO₂–CO₂ group and the highest in the LO₂–CO₂ group. Lower plasma chloride and sodium levels were observed in the CO₂ groups relative to the respective oxygenation groups during the FW period, while plasma chloride and sodium levels were normalised to equal levels for all groups after 44 days in SW. No significant differences were found among treatments for blood concentrations of red blood cells, haemoglobin, potassium and glucose during the experiment.By termination of the FW period, the HO₂ group had significantly higher body weight than all other groups (p < 0.05), with specific growth rate significantly higher than the CO₂ groups (p < 0.05). Further, the condition factor was significantly lower in all the CO₂ groups at the end of the FW period compared to the control and normcapnia groups (p < 0.05). Although variable among replicates, occurrence of nephrocalcinosis was 10 times higher in the hypercapnia groups than in the control and normcapnia groups. Mortality was negligible (< 2.0%) during the trial, and most of the mortality occurred following SW transfer.     

Relevance of dietary oil source for contraction and quality of pre-rigor filleted Atlantic cod, Gadus morhua

Rigor contraction and quality development were studied during storage of pre-rigor fillets of farmed Atlantic cod (body weight 2 kg). For eight weeks prior to slaughtering, the fish were fed diets containing either 100% fish oil (M-group) or 60% fish oil and 40% soybean oil (S-group). Filleting was performed 0.5 h after slaughtering and the fillets were stored at 6 °C for 48 h post-mortem. The contraction rate was faster for the S-group, but after 48 h storage the contraction was 21% of the initial fillet length for both fish groups. The ATP content analysed 1 h post-mortem was lower of the S-group (4.5 μm g^− 1 ww) compared with the M-group (6.1 μm g^− 1 ww). After 16 h, the ATP content was similar for both fish groups (1.7-2.2 μm g^− 1 ww). The muscle pH analysed 1 h post-mortem was 0.2 unit lower of the S-group (pH 6.9) than of the M-group (pH 7.1). From 8 to 12 h, the pH fell significantly to 6.3 and 6.6 for the S-group and M-group, respectively. From 24 h and onwards, the pH was similar of both fish groups (pH 6.2). Texture development differed significantly due to dietary treatment. The S-group had highest initial breaking force, demonstrating that the texture of this group was firmer immediately after slaughtering. The breaking force of the S-group dropped to a stable level after 4 h, whereas the breaking force of the M-group decreased continuously during the storage period. The breaking force was similar of both groups after 16 h storage. The L*-value (lightness) increased during the first 4-6 h storage. From 8 to 16 h, the L*-value was stable or slightly decreasing. The L*-value was consistently higher of the M-group. In conclusion, dietary inclusion of soybean oil resulted in faster energy depletion post-mortem, faster rigor contraction, faster reduction of the breaking strength and lower L*-values.     

Effects of Carlin tagging and fin clipping on survival of Atlantic salmon (Salmo salar L.) released as smolts

During the period 1976–1979, in total 2567 wild migrating smolts of Atlantic salmon were Carlin-tagged, 2528 were adipose fin-clipped and 2309 individuals were released unmarked into the River Imsa, S.W. Norway. The smolts were caught in a permanent Wolf trap. The adult return rate to the river was highest for unmarked and lowest for Carlin-tagged fish. The main reason for this is probably a mortality of smolts due to handling, anaesthesia and tagging.     

气候变化对南海浮游植物藻华形成的影响研究进展

围绕中国南海丰富的渔业资源,采用16S rDNA扩增子测序技术,分析了南海近岸硬骨鱼类鳃组织微生物群落分布特征,并探讨了7个不同站点细菌群落结构的差异。结果显示,测序共获得有效拼接片段 (Clean tags) 2 952 366条,平均每个文库56 776条。分别在门、属水平对其优势类群进行了分析,其中门水平上变形菌门 (Proteobacteria) 最高 (71.3%),属水平上变形菌门的不动杆菌属 (Acinetobacter) 最高 (17.2%)。不同站点的α多样性具有显著差异,其中I9和H8站点的物种丰富度 (Chao1指数) 最高,D3站点的多样性 (Shannon指数) 最高。不同站点来源样品之间的β多样性具有显著差异 (P<0.05),但在宿主分类的目水平上无显著差异 (P>0.05)。中国南海近岸硬骨鱼鳃组织中的细菌群落组成丰富,采样站位相比宿主分类对鳃组织上细菌群落具有更重要的影响,它们可能在辅助宿主营养物质转运及代谢方面发挥积极作用。     

Microsatellite analysis in domesticated and wild Atlantic salmon (Salmo salar L.): allelic diversity and identification of individuals

Samples of wild and domesticated salmon in Norway were genotyped at 12 microsatellite loci to compare allelic variability and investigate the potential of microsatellite markers for identification of individuals. The following loci were amplified: Ssa20, Ssa62NVH, Ssa71NVH, Ssa90NVH, Ssa103NVH, Ssa105NVH, SsaF43; Ssa20.19; Ssa13.37; SsOSL85; Ssa197; Ssa28. All domesticated strain samples displayed reduced variability compared to wild salmon. On average 58% of the allelic richness observed within the four wild stocks were present in the samples taken from domesticated strains. No systematic differences in heterozygosity were observed between samples representing the two groups.

Pairwise genetic distances, as estimated by Fst values and Nei [1978] was 2–8 times higher among domesticated strains than among wild strains. Among the wild stocks, the highest genetic distances were observed between the river Neiden, located in northern Norway, and the other wild stocks located in the southwest of Norway.

Assignment tests indicated that the wild and domesticated salmon could be distinguished with high precision. Less than 4% of domesticated salmon were misassigned as wild salmon, and less than 3% of wild fish were misassigned as domesticated salmon. Fish from individual domesticated strains were identified with similarly high precision. Assignment to wild salmon stocks was less accurate, with the exception of the sample taken from the river Neiden, for which 93% of the individuals were correctly assigned.     

Differences in sea migration between wild and reared Atlantic salmon (Salmo salar L.) in the Baltic Sea

The effect of origin, smolt size and year of release on the sea migration pattern of Atlantic salmon (Salmo salar L.) in the Baltic Sea was examined by tagging experiments conducted in 1991–1993 on wild and reared smolts of the Simojoki river salmon stock. The tag recovery data analysed by log-linear models revealed significant differences in both spatial and temporal sea migrations between the wild and reared salmon; the variation was attributed to the year of release and to the origin of the fish. Grilse accounted for the majority of reared returners (76%) but for a smaller proportion (46%) of the wild fish. The effect of smolt size could be studied only in the smolt groups tagged in 1991. Wild fish were more frequently (71%) caught in the Baltic Main Basin than were reared fish (51%) during their second sea year, and the size variation between wild and reared smolts did not explain the recovery site. No such differences in spatial distribution were found during the third sea year. The tagging place (hatchery/trap) of the reared fish did not affect their later sea migration. The differences in sea migration patterns suggest that the wild salmon are more vulnerable to the intensive salmon fishery in the Baltic Main Basin than are reared fish.     

Dietary phytase supplementation and the utilisation of phosphorus by Atlantic salmon (Salmo salar L.) fed a canola-meal-based diet

The effect of phytase supplementation to a canola-meal-based diet on phosphorus utilisation in Atlantic salmon was studied in a two-by-two factorial design. Diets were prepared without phytase or inorganic phosphorus supplementation, with phytase, with supplemental inorganic phosphorus and with both phytase and supplemental inorganic phosphorus. Available phosphorus was set below requirement and the total phosphorus set to meet requirements for salmonids. After 12 weeks, there were no significant differences in survival, feed intake and weight gain between diets. There was an interaction effect between supplements on bone ash, bone phosphorus and whole-body phosphorus so that adding phytase, inorganic phosphorus, or both resulted in significantly (P<0.05) higher values for these parameters. An interaction effect was also observed for phosphorus digestibility, phosphorus retention efficiency and phosphorus load. Phosphorus digestibility and retention efficiency were significantly (P<0.05) higher, and phosphorus load was significantly (P<0.05) lower in fish fed the phytase supplemented diet compared with diets containing supplemental inorganic phosphorus. In conclusion, phytase increased phosphorus availability, therefore reducing the need to add inorganic phosphorus and reducing phosphorus waste from plant-meal-based diets for Atlantic salmon.     

Lower prevalence of fin erosion in mature than in immature Atlantic salmon (Salmo salar) parr

Samples of hatchery-reared Atlantic salmon parr (age 0+ and 1+) from two different Norwegian river strains were investigated for connections between sexual maturity and prevalence of dorsal fin ray erosion. Mature males showed consistently lower prevalence as well as better recovery than immature males. Among the immature fish, no differences were detected between males and females. The results are discussed relative to morphological and physiological changes in maturing salmon parr.