A summary of the impact of acid rain on atlantic salmon (Salmo salar) in Canada

Within the present North American range of Atlantic salmon, severe acid rain effects are limited to the Southern Upland area of Nova Scotia. In the Southern Upland, long range transport of H₂SO₄ has caused many rivers to decline in pH to the point where their Atlantic salmon stocks have been destroyed or much diminished. Chemical records show a declining pH trend in N.S. rivers since the early 1950s. Eighty % of the annual variation in H⁺ concentration can be accounted for by a multiple linear regression model on excess sulphate, total Al and organic anions. It is technically feasible to restore the acidified salmon habitat by the addition of limestone; the total cost of mounting a liming program to restore the lost habitat has been estimated at $4.75 × 10⁶ yr^?1. The pre-acidification Atlantic salmon production capacity of the Southern Upland was estimated from physical habitat surveys and tag return data to be about 45 000 fish yr^?1. Acidification has caused a 50% decline to the current production level of about 23 000 fish yr^?1. The costs of the liming program, when compared to the economic benefits of the anticipated salmon enhancement, are economically unjustifiable. The eradication of salmon from such large regions will hinder future programs to reestablish the species in their former range when pollution of the atmosphere is eventually brought under control. Present plans are for a small liming program to establish a series of refuges for the preservation of nuclei of native salmon stocks.     

Multiple compound quality index for cold-smoked salmon (Salmo salar) developed by multivariate regression of biogenic amines and pH

Production of biogenic amines during chill storage of 12 lots of cold-smoked salmon was studied. These data allowed for a multiple compound quality index to be developed by multivariate regression (partial least square regression). The quality index was based on concentrations of cadaverine, histamine, putrescine, and tyramine and pH and showed good correlation with sensory assessments. Biogenic amines were indicators of spoilage rather than casual agents of spoilage off-flavors. Four different biogenic amine profiles were found at the time of spoilage in cold-smoked salmon. These were the results of differences in the spoilage microflora. Histamine was detected above regulatory limits but below toxic levels. Measurements of salt and dry matter for calculation of water phase salt could be substituted by rapid water activity measurements.     

放养规格对银化期大西洋鲑生长的影响及生理响应机理

内分泌系统在调节大西洋鲑(Salmo salar L.)的银化过程中,除了要尽快建立更高效的渗透调节机制外,鱼体自身的生理反应变化还要更好地适应降海后的生活。试验研究了平均体质量(30.25±2.12)g(SW1)、(24.27±1.59)g(SW2)和(18.05±2.46)g(SW3)大西洋鲑,1~42 d光照周期为12L:12D;43~84 d为全光照下(24L:0D)的生长及生理响应机理。试验结果表明,SW2组大西洋鲑的肥满度、日增质量、饲料转化率、净增质量最高,与其他组差异显著(P0.05)。SW2组体质量、体长特定生长率均显著高于其他处理组(P0.05),各组间体质量、体长变异系数差异显著(P0.05)。试验前6周不同处理组大西洋鲑体长变异系数差异不显著(P0.05)。后6周全光照时,SW1、SW2组体长变异系数显著增加,且SW1组显著高于其他组(P0.05)。SW3组的大西洋鲑体质量变异系数变化较大。前6周光照期为12L:12D时,SW1、SW2两组体质量变异系数差异不显著(P0.05),后6周改为全光照时,3个处理组间体质量变异系数差异减小。但在84 d时,SW3组体质量变异系数显著高于其他组(P0.05)。随着养殖规格的增大,血红蛋白浓度升高,红细胞数目增加,说明鱼体需氧量增加。SW3组白细胞数目、淋巴细胞数目和中性粒细胞数目最高,表明鱼体抗病能力强。红细胞数目在SW1和SW2组间无显著差异(P0.05),但均显著高于SW3组(P0.05)。血栓细胞数目随着放养规格的增加而下降,且在3个规格组之间差异显著(P0.05)。中性粒细胞数目在3个规格组之间并没有显著性差异(P0.05)。SW2组总蛋白、白蛋白含量最高,且各组间差异显著(P0.05)。总胆固醇、甘油三酯浓度随鱼体规格增大而增加(P0.05),表明大西洋鲑血液和体内对能量的利用增强。SW2组代谢产物尿酸、尿素浓度最高,且SW1、SW2组的浓度值均显著高于SW3组(P0.05)。SW3组大西洋鲑血清中总胆红素显著高于其他两组(P0.05)。各组间大西洋鲑血清中葡萄糖浓度没有显著性差异(P0.05)。SW3组肌酸激酶浓度最高,但各组间没有显著性差异(P0.05)。该研究结果建议选择体质量(24.27±1.59)g的大西洋鲑开始银化,利于优化养殖条件、以较低成本增加单位水体养殖产量和苗种规模化生产。     

Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil

A significant proportion of the total nutrient in soil solution can be bound to organic molecules and these often constitute a major loss from soil to freshwater. Our purpose was to determine whether chemical extractants used for measuring inorganic N could also be used to quantify dissolved organic nitrogen (DON) and carbon (DOC) in soil. In a range of soils, DOC and DON were extracted with either distilled water or 2 M KCl and the amount recovered compared with that present in soil solution recovered by centrifugal-drainage. The recovery of DON and DOC from soil was highly dependent upon the method of extraction. Factors such as soil sampling strategy (number of samples over space and time), sample preparation (sieving and drying), soil storage, extraction temperature, shaking time, and soil-to-extractant volume ratio all significantly affected the amount of DOC and DON extracted from soil. To allow direct comparison between independent studies we therefore propose the introduction of a standardized extraction procedure: Replicate samples of unsieved, field-moist soil extracted as soon as possible after collection with distilled water, 0.5 M K₂SO₄ or 2 M KCl at a 1:5 w/v ratio for 1 h at 20 °C.     

Fish kills of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in an acidified river of SW Norway

This paper documents population responses of Atlantic salmon and brown trout to fish kills in River Vikedal, an acidified river in SW Norway. The angling statistics show that the adult population of Atlantic salmon in the river has decreased to low numbers during recent years, whereas catches of migrant brown trout have increased in the same period. A total of 659 dead salmon and trout were either collected or observed during spring snowmelt in the years 1982–1985. Parr suffered the highest mortality, and most large specimens. Only a few dead kelts were registered. In the springs of most unfavourable water quality and most severe episods of fish kills (1983 and 1984), salmon parr mortality were significantly higher than that of brown trout. Episodic death of parr in the spring is thought to be an important cause of the reduction in the adult stock of Atlantic salmon in the river during recent years.     

The effects of liming on juvenile stocks of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in a Norwegian river

The effects of liming on juvenile stocks of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in the river Vikedalselva in southwestern Norway were assessed. From 1987 to 1989, the river was limed only during the spring snow melt, and pH varied in the range between 5.5 and 7.0. In 1990 to 1993, the river was limed to pH 6.2 from 15 February to 1 June and to pH 5.7 during the rest of the year. Since 1994, the pH during late winter and spring was maintained above 6.5. Prior to liming fish kills were evident during spring snow melt, but these have not occurred since liming. Electrofishing in the autumn between 1981 and 1994 showed no significant change in densities of juvenile salmon and brown trout after liming, mean densities ranged between 19–50 and 9–32 individuals 100 m^–2 respectively. A significant linear correlation between production and biomass of both species was found, indicating that factors directly controlling density affect juvenile production and cause production to remain below carrying capacity. In spite of a clear increase in pH and a reduction in the concentration of labile aluminium after liming, the conditions still do not seem to be optimal for juvenile salmonids. We suggest that a complexity of different factors impose limitations on fish production in the river: inadequate egg deposition, environmental factors such as water temperature and flow, osmoregulatory failure in mixing zones between limed and acidic water and gill damage through deposition of aluminium and iron. However, there are several indications of a reduction in toxic effects after the pH was raised to 6.5 during spring snow melt.     

Influence of sulfur amino acids on the volatile and nonvolatile components of cooked salmon (Salmo salar)

Volatile and nonvolatile compounds, which could contribute to flavor, were analyzed in salmon. One hundred twenty-three volatile compounds were identified in the headspace of two different samples of cooked salmon, including lipid-derived volatiles, Maillard-derived volatiles, sulfur volatiles, Strecker aldehydes, nitrogen heterocyclic compounds, terpenes, and trimethylamine. Significant differences between samples were found for 104 of the volatiles. Although the levels of free cysteine and methionine were low in the salmon, sulfur volatiles were formed in the cooked fish, demonstrating that there were sufficient sulfur amino acids present for their formation. Notable differences in sulfur compounds between the samples suggested that small changes in sulfur amino acids could be responsible. When this hypothesis was tested, salmon heated with cysteine had increased levels of many thiophenes, thiazoles, alicyclic sulfides, and nitrogen heterocycles. With the addition of methionine, levels of dimethyl sulfides, two alicyclic sulfides, pyrazines, some unsaturated aldehydes, and alcohols and 2-furanmethanethiol increased. The largest difference found among the nonvolatile (low molecular weight water-soluble) compounds was in inosine monophosphate.     

Baking reduces prostaglandin, resolvin, and hydroxy-fatty acid content of farm-raised Atlantic salmon (Salmo salar)

The consumption of seafood enriched in n-3 polyunsaturated fatty acids (PUFA) is associated with a decreased risk of cardiovascular disease. Several n-3 oxidation products from eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (22:6n-3) have known protective effects in the vasculature. It is not known whether the consumption of cooked seafood enriched in n-3 PUFA causes appreciable consumption of lipid oxidation products. We tested the hypothesis that baking Atlantic salmon (Salmo salar) increases the level of n-3 and n-6 PUFA oxidation products over raw salmon. We measured the contents of several monohydroxy-fatty acids (MHFA), prostanoids, and resolvins. Our data demonstrate that baking did not change the overall total levels of MHFA. However, baking resulted in selective regioisomeric loss of hydroxy fatty acids from arachidonic acid (20:4n-6) and EPA, while significantly increasing hydroxyl-linoleic acid levels. The contents of prostanoids and resolvins were reduced several-fold with baking. The inclusion of a coating on the salmon prior to baking reduced the loss of some MHFA but had no effect on prostanoid losses incurred by baking. Baking did not decrease n-3 PUFA contents, indicating that baking of salmon is an acceptable means of preparation that does not alter the potential health benefits of high n-3 seafood consumption. The extent to which the levels of MHFA, prostanoids, and resolvins in the raw or baked fish have physiologic consequence for humans needs to be determined.     

Biochemical and functional properties of Atlantic salmon (Salmo salar) muscle proteins hydrolyzed with various alkaline proteases

Protein hydrolysates (5, 10, and 15% degrees of hydrolysis) were made from minced salmon muscle treated with one of four alkaline proteases (Alcalase 2.4L, Flavourzyme 1000L, Corolase PN-L, and Corolase 7089) or endogenous digestive proteases. Reaction conditions were controlled at pH 7.5, 40 degrees C, and 7.5% protein content, and enzymes were added on the basis of standardized activity units (Azocoll units). Proteases were heat inactivated, insoluble and unhydrolyzed material was centrifuged out, and soluble protein fractions were recovered and lyophilized. Substrate specificities for the proteases was clearly different. Protein content for the hydrolysates ranged from 71.7 to 88.4%, and lipid content was very low. Nitrogen recovery ranged from 40.6 to 79.9%. The nitrogen solubility index was comparable to that of egg albumin and ranged from 92.4 to 99.7%. Solubility was high over a wide range of pH. The water-holding capacity of fish protein hydrolysates added at 1.5% in a model food system of frozen minced salmon patties was tested. Drip loss was on average lower for the fish protein hydrolysates than for egg albumin and soy protein concentrate, especially for Alcalase hydrolysates. Emulsification capacity for fish protein hydrolysates ranged quite a bit (75-299 mL of oil emulsified per 200 mg of protein), and some were better than soy protein concentrate (180 mL of oil emulsified per 200 mg of protein), but egg albumin had the highest emulsifying capacity (417 mL of oil emulsified per 200 mg of protein). Emulsification stability for fish protein hydrolysates (50-70%) was similar to or lower than those of egg albumin (73%) or soy protein concentrate (68%). Fat absorption was greater for 5 and 10% degrees of hydrolysis fish protein hydrolysates (3.22-5.90 mL of oil/g of protein) than for 15% hydrolysates, and all had greater fat absorption than egg albumin (2. 36 mL of oil/g of protein) or soy protein concentrate (2.90 mL of oil/g of protein).     

Use of two-dimensional electrophoresis to evaluate proteolysis in salmon (Salmo salar) muscle as affected by a lactic fermentation

Two-dimensional electrophoresis was used to study proteolysis in salmon fillets inoculated or not with the starter culture Lactobacillus sake LAD. Protein fragments appeared increasingly with time in both samples, indicating that the main quantitative changes were due to endogenous enzymes. In the most acidic zone (pI = 4-6. 20) particularly, proteolysis was overall independent from processing. In contrast, fermentation had a significant effect in the pH range 6.20-8.35, suggesting a specificity of the bacterial proteases of L. sake toward alkaline to slightly acidic proteins. Furthermore, fragments surrounding tropomyosin (apparent pI = 4.70) appeared in fermented samples, indicating that the protein may be a suitable substrate for the metabolism of L. sake LAD.     

Effects of different cooking procedures on lipid quality and cholesterol oxidation of farmed salmon fish (Salmo salar)

Salmon fillets were steamed, or pan-fried without oil, with olive oil, with corn oil, or with partially hydrogenated plant oil. The exchange between the salmon and the pan-frying oils was marginal, but it was detectable as slight modifications in the fatty acid pattern and the tocopherol contents according to the oil used. Primary and secondary oxidation products were only slightly increased or remained unchanged, which indicated a slight lipid oxidation effect due to the heating procedures applied. The same was observed for tocopherol levels, which remained almost stable and were not affected by the oxidation process. The sum of cholesterol oxidation products (COPs) increased after the heating processes from 0.9 microg/g in the raw sample to 6.0, 4.0, 4.4, 3.3, and 9.9 microg/g extracted fat in pan-fried without oil, with olive oil, corn oil, partially hydrogenated plant oil, and steamed, respectively. A highly significant correlation was found between the fatty acid pattern and the total amount of COPs (r2 = 0.973, p < 0.001). No change has been determined in the n-3 fatty acids content and in the polyunsaturated/saturated-ratio of the cooked salmon fillets. Moderate pan-frying (6 min total) and steaming (12 min) of salmon did not accelerate lipid oxidation but significantly increased the content of COPs. The highest increase of COPs was found through steaming, mainly due to the longer heat exposure. The used frying oils did not influence the outcome; no significant difference between heat treatment with or without oil has been determined.     

Water quality requirement of Atlantic salmon (Salmo salar) in water undergoing acidification or liming in Norway

Atlantic salmon are severely affected by acidification in Norway. Water quality criteria for the salmon have to be based on the most sensitive stage, the smolt stage. The sensitivity to acidic water increases enormously during smolting, the seawater tolerance being especially vulnerable. Even moderately acidic water (pH about 6) with low inorganic monomeric aluminium (LA1) concentrations (<20μg. L^?1) and short-term episodes may be harmful. Mixing zones in limed or unlimed rivers may also represent a problem for seaward migrating smolts. In limed salmon rivers, the national liming goal has been increased to pH 6.5 during smolting (1 February to 1 July) and to 6.2 the rest of the year as a result of our experiments. In contrast to what has been found for brown trout, salmon strains originating from watercources undergoing acidification were not more tolerant than those from non-acidic watercourses. At the moment no such “tolerant” strains are available for restocking limed rivers in Norway.     

Base additions to flowing acidic water: Effects on smolts of Atlantic salmon (Salmo salar L.)

Acidic, Al-rich soft water (pH=5.1, Ca=1.0 mg L^?1 and labile Al=160 μg Al L^?1) was treated by addition of soda (Na ₂Co₃) and lime slurry (CaCO₃). Seven different water qualities of each type of treatment, covering the pH-range 5.1 to 8.2, were prepared in a flow-through system. Smolts of Atlantic salmon (Salmo salar L.) were used as test fish. In both types of treatment, mortality occurred at all pH-levels below 6.05. Above pH 6.05 no mortality occurred using lime slurry. Using soda, 10 % mortality occurred within 48 hr at pH above 7 due to the toxicity of aluminate at low levels of Ca. Plasma chloride levels indicated no physiological stress in the pH-range 6.45 to 7.0.     

Water distribution in brine salted cod (Gadus morhua) and salmon (Salmo salar): a low-field 1H NMR study

Low-field (LF) (1)H NMR T 2 relaxation measurements were used to study changes in water distribution in lean (Atlantic cod) and fatty (Atlantic salmon) fish during salting in 15% NaCl and 25% NaCl brines. The NMR data were treated by PCA, continuous distribution analysis, and biexponential fitting and compared with physicochemical data. Two main water pools were observed in unsalted fish, T 21, with relaxation times in the range 20-100 ms, and T 22, with relaxation times in the range 100-300 ms. Pronounced changes in T 2 relaxation data were observed during salting, revealing changes in the water properties. Salting in 15% brine lead to a shift toward longer relaxation times, reflecting increased water mobility, whereas, salting in saturated brines had the opposite effect. Water mobility changes were observed earlier in the salting process for cod compared to salmon. Good linear correlations ( F 相似文献   

Effects of storage atmosphere and heme state on the color and visible reflectance spectra of salmon ( Salmo salar ) fillets

It has previously been observed that the color of mackerel muscle is dependent on the status of heme as myoglobin and hemoglobin and hence the storage atmosphere. This study gives strong indications of this being the case also in salmon. Three different storage conditions were used to promote the oxidized, reduced, and carbon monoxide (CO) bound forms of heme in salmon and mackerel fillets. Color determination (instrumental color analysis, imaging, and sensory evaluation) and spectroscopic measurements were performed to study how spectral changes corresponded to color variations. Storage in CO significantly increased the redness in mackerel. This was also seen in salmon to such a degree that it was visible over normal levels of salmon carotenoids. Air storage increased the yellowness and reduced the redness in mackerel, but this effect was partly concealed in salmon by the astaxanthin absorption. The spectral differences due to storage condition could be ascribed to the spectral features characterizing heme of different oxidation states and bound to different ligands. The status of heme should therefore always be considered when experiments related to salmon color are performed. The findings could help in the understanding, control, and prediction of color loss in salmon during processing, storage, and transport.     

Effects of brine salting with regard to raw material variation of Atlantic salmon (Salmo salar) muscle investigated by Fourier transform infrared microspectroscopy

Atlantic salmon fillets differing with regard to raw material characteristics (prerigor, postrigor, frozen/thawed) and salt content were investigated by FT-IR microspectroscopy and light microscopy. Local variation within each salmon fillet was further taken into account by sampling from the head and tail part separately as they vary in fat and moisture content. The highest salt uptake was achieved for frozen/thawed quality during brine-salting with 16% NaCl for 4 h, while the uptake was least for prerigor fish. At the same time, salting caused muscle fiber swelling of about 10% for both frozen/thawed and postrigor qualities. Differences in the FT-IR amide I spectral region were observed implying a change in the muscle protein secondary structure. Prerigor was least affected by brine-salting, having a final salt concentration of 2.2%, while postrigor had a NaCl content of 3.0% and frozen/thawed of 4.1%. Local variation within the fillets had an effect on the amide I absorption characteristics before as well as after salting. Salt uptake of the samples was affected by raw material quality and at the same time the degree of swelling of the myofibers was influenced by raw material character.     

Significance of volatile compounds produced by spoilage bacteria in vacuum-packed cold-smoked salmon (Salmo salar) analyzed by GC-MS and multivariate regression

Changes were studied in the concentration of 38 volatile compounds during chilled storage at 5 degrees C of six lots of commercially produced vacuum-packed cold-smoked salmon and sterile cold-smoked salmon. The majority of volatile compounds produced during spoilage of cold-smoked salmon were alcohols, which were produced by microbial activity. Partial least-squares regression of volatile compounds and sensory results allowed for a multiple compound quality index to be developed. This index was based on volatile bacterial metabolites, 1-propanol and 2-butanone, and 2-furancarboxaldehyde produced by autolytic activity. Only a few of the volatile compounds produced during spoilage of cold-smoked salmon had an aroma value high enough to indicate contribution to the spoilage off-flavor of cold-smoked salmon. These were trimethylamine, 3-methylbutanal, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-penten-3-ol, and 1-propanol. The potency and importance of these compounds was confirmed by gas chromatography-olfactometry. The present study provides valuable information on the bacterial reactions responsible for spoilage off-flavors of cold-smoked salmon, which can be used to develop biosensors for on-pack shelf-life determinations.     

Olfactometric determination of the most potent odor-active compounds in salmon muscle (Salmo salar) smoked by using four smoke generation techniques

The volatile compounds of salmon fillets smoked according to four smoked generation techniques (smoldering, thermostated plates, friction, and liquid smoke) were investigated. The main odor-active compounds were identified by gas chromatography coupled with olfactometry and mass spectrometry. Only the odorant volatile compounds detected by at least six judges (out of eight) were identified as potent odorants. Phenolic compounds and guaiacol derivatives were the most detected compounds in the olfactometric profile whatever the smoking process and could constitute the smoky odorant skeleton of these products. They were recovered in the aromatic extracts of salmon smoked by smoldering and by friction, which were characterized by 18 and 25 odor-active compounds, respectively. Furannic compounds were more detected in products smoked with thermostated plates characterized by 26 odorants compounds. Finally, the 27 odorants of products treated with liquid smoke were significantly different from the three others techniques applying wood pyrolysis because pyridine derivatives and lipid oxidation products were perceived in the aroma profile.     

Soyasaponins resist extrusion cooking and are not degraded during gut passage in Atlantic salmon (Salmo salar L.)

The stability of soyasaponins in fish feed formulations was investigated. The level of soyasaponin Ab, Bb, Bc, Ba-2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (Ba-DDMP), Bb-DDMP, and Bc-DDMP was quantified in 15 samples of defatted soybean meal, two full fat soybean meals, and two soybean protein concentrates by reverse phase high-performance liquid chromatography. The total level of saponins in the 15 samples of commercial defatted soybean meal ranged from 4.8-6.8 micromol/g (5.1-7.0 g/kg). The two full fat meals contained 4.4 and 4.7 micromol/g whereas no saponins could be detected in the alcohol-extracted soybean protein concentrates. Fifteen batches of fish feed containing 20% defatted soybean meal were produced by twin-screw extrusion from the 15 different samples of defatted soybean meal. Extrusion did not reduce the total level of group B saponins, but the ratio between DDMP-conjugated group B saponins and non-DDMP-conjugated group B saponins was slightly reduced. A soybean-containing diet was fed to seawater adapted Atlantic salmon for 9 weeks. Yttrium oxide was included in the feed as an inert marker in order to estimate the disappearance of saponins during gut passage. High levels of intact non-DDMP-conjugated group B soyasaponins were found in feces whereas only low levels of DDMP-conjugated saponins could be detected. The overall disappearance of saponins was close to zero, and the concentration of intact saponins in dry feces reached levels several fold higher than dietary levels. The present work demonstrates that non-DDMP-conjugated group B soyasaponins resist extrusion cooking and remain intact during gut passage in Atlantic salmon. The latter is contrary to earlier findings in endothermic animals.     

Estimating dissolved organic carbon in natural waters by UV absorbance (254 nm)

A close correlation exists between dissolved organic carbon (DOC) concentration and UV absorbance at 254 nm (A₂₅₄) in natural waters. DOC and A₂₅₄ were measured for soil solutions, throughfall, stemflow, and surface waters collected from a forested site located in eastern Austria. The slopes of lines determined by linear regression of DOC versus UV absorbance were very similar to those determined for wet deposition and throughfall samples collected in Nordrhein-Westfalen, Germany by Bartels (1988). The intercept of the regression line in the current study indicates that approximately 1 mg L¹ of non-UV-absorbing DOC is present; it is suggested that this is due to saturated aliphatic compounds such as acetate or formate.