Egg Thiamine Status of Lake Ontario Salmonines 1995–2004 with Emphasis on Lake Trout

Alewives (Alosa pseudoharengus), the major prey fish for Lake Ontario, contain thiaminase. They are associated with development of a thiamine deficiency in salmonines which greatly increases the potential for developing an early mortality syndrome (EMS). To assess the possible effects of thiamine deficiency on salmonine reproduction we measured egg thiamine concentrations for five species of Lake Ontario salmonines. From this we estimated the proportion of families susceptible to EMS based on whether they were below the ED20, the egg thiamine concentration associated with 20% mortality due to EMS. The ED20s were 1.52, 2.63, and 2.99 nmol/g egg for Chinook salmon (Oncorhynchus tshawytscha), lake trout (Salvelinus namaycush), and coho salmon (Oncorhynchus kisutch), respectively. Based on the proportion of fish having egg thiamine concentrations falling below the ED20, the risk of developing EMS in Lake Ontario was highest for lake trout, followed by coho (O. kisutch), and Chinook salmon, with the least risk for rainbow trout (O. mykiss). For lake trout from western Lake Ontario, mean egg thiamine concentration showed significant annual variability during 1994 to 2003, when the proportion of lake trout at risk of developing EMS based on ED20 ranged between 77 and 100%. Variation in the annual mean egg thiamine concentration for western Lake Ontario lake trout was positively related (p < 0.001, r² = 0.94) with indices of annual adult alewife biomass. While suggesting the possible involvement of density-dependent changes in alewives, the changes are small relative to egg thiamine concentrations when alewife are not part of the diet and are of insufficient magnitude to allow for natural reproduction by lake trout.     

Dietary Pigmentation and Deposition of α-Tocopherol and Carotenoids in Rainbow Trout Muscle and Liver Tissue

Rainbow trout (Oncorhynchus mykiss) were fed diets supplemented with canthaxanthin, oleoresin paprika and α-tocopherol. Canthaxanthin was more efficiently absorbed (3.8–7.9 mg/kg) in the flesh of rainbow trout than the paprika carotenoids (2.4–3.1 mg/kg). With increased pigmentation, decrease in lightness (L*) and hue angle, and increase in redness (a*) of the muscle were observed. Canthaxanthin produced more desirable reddish-pink color. Deposition of α-tocopherol in liver and muscle tissue increased with increase in dietary α-tocopheryl acetate. Fish receiving lower α-tocopheryl acetate reached maximum deposition levels earlier than those fed higher levels. There was no effect of α-tocopherol and carotenoid levels on muscle fatty acid composition.     

Modified atmosphere packaging of filleted rainbow trout

Shelf‐lives of filleted rainbow trout (Oncorhynchus mykiss) packaged in over‐wrap, vacuum and gas mixture conditions and stored at 1 ± 1 °C were compared by measurement of pH, total volatile bases (TVB), hypoxanthine content, lipid oxidation (TBARS value), superficial counts of aerobic psychrotrophic flora and sensory analysis (colour, odour and flavour). The gas mixtures evaluated were 10% O₂ + 50% CO₂ + 40% N₂, 10% O₂ + 50% CO₂ + 40% Ar, 20% O₂ + 50% CO₂ + 30% N₂, 20% O₂ + 50% CO₂ + 30% Ar, 30% O₂ + 50% CO₂ + 20% N₂ and 30% O₂ + 50% CO₂ + 20% Ar. Sensory quality deterioration was delayed and bacterial growth as well as increases in pH, TVB and hypoxanthine levels were reduced by modified atmosphere packaging (MAP). Lipid oxidation was higher in gas packages with 20 and 30% O₂ than in those with 10% O₂. Vacuum‐packed fillets presented the lowest TBARS values. In summary, MAP gave rise to a significant extension of shelf‐life when compared with vacuum and over‐wrap packaging. No significant differences were found between the packages containing either N₂ or Ar. The best evaluated atmosphere consisted of 10% O₂ + 50%CO₂ + 40% N₂/Ar. © 2002 Society of Chemical Industry     

Frozen Storage Quality of Rainbow Trout (Oncorhynchus mykiss) as Affected by Oxygen, Illumination, and Fillet Pigment

We investigated the influence of packaging materials with high, medium and low oxygen transmission rates (OTR) on the development of 2-thiobarbituric acid-reactive substances (TBARS) and astaxanthin retention in rainbow trout fillets. Three different levels of astaxanthin, during dark or illuminated frozen storage were studied. Samples were analyzed after 17, 29 and 36 wk frozen storage. Rancidity developed more rapidly in packages with high OTR. This effect was more pronounced in illuminated samples, also verified by sensory evaluation. Fillets with highest astaxanthin content reached maximum TBARS after 29 wk. The two less pigmented sample groups reached maximum after 17 wk frozen storage, indicating antioxidative effects of astaxanthin.     

Frozen Storage and Thawing Methods Affect Biochemical and Sensory Attributes of Rainbow Trout

Rainbow trout were subjected to four thawing treatments after being stored at ?18°C and -40°C for 0, 3, 7, 13 and 18 mo. Membrane integrity was estimated as the volume of centrifuged tissue fluid (CTF) and by lysosomal β-N-acetylglucosaminidase (NAG) activity in CTF. Slow thawing, in air at 5°C resulted in higher NAG activity in CTF and a larger volume of CTF than fast thawing, at 25°C in water, independent of storage time. After 3 or more months storage, a higher NAG activity in CTF and a larger volume of CTF were found in all -18°C stored samples compared to that at -40°C. Sensory evaluation confirmed differences between trout stored at -18°C and at -40°C for 18 mo.     

Modified Atmosphere-packed Marinated Chicken Breast and Rainbow Trout Quality as Affected by Package Leakage

Marinated chicken breast pieces and sliced rainbow trout were packed in modified atmosphere and stored to measure effects of package leakage. The sensory shelf life of products decreased slowly but linearly as leakage rate increased, with exception of the appearance of sliced rainbow trout, which was not affected by leakage rate. The concentration of ethanol in head space was a potential indicator of spoilage and package leakage for both products. The presence of dimethylsulfide indicated spoilage of chicken fillet and acetone indicated leakage in sliced trout packages. A redox leakage color-indicator functioned properly in package lids.     

Microstructure and instrumentally measured textural changes of rainbow trout (Oncorhynchus mykiss) gravads during production and storage

BACKGROUND: Gravad fish belong to a group of low‐processed products obtained from fresh fish by rubbing fillets with a mixture of sugar and salt and then placing them in cold storage. Little is known about changes in the tissue during the production and storage of gravads. The aim of the present study was to investigate the microstructural and textural changes in rainbow trout (Oncorhynchus mykiss) gravad during processing and vacuum storage at 3 °C and ?30 °C. RESULTS: Microscopic observations of gravad showed greater compactness of structure when compared with raw trout muscle, characterised by the disappearance of the divisions between adjoining myofibrils in gravad. Freezing, on the other hand, caused the myofibrils to again become more clearly distinguishable despite being partly agglomerated into lamellae. The above changes in structure were accompanied by changes in the textural and rheological properties of the product. It was observed that the texture profile (TPA) changed, resulting in an increase in the cohesiveness and chewiness of the gravads when compared to the raw fillets. There was also a lowering of stress decay during the relaxation test and a decrease in the value of the storage modulus (G′) as analysed by oscillatory rheometry. Further changes observed during storage were mainly concerned with an increase in the hardness and chewiness of gravads. CONCLUSION: Gravading significantly changes the rainbow trout fillets by making the microstructure more compact. This process is accompanied by changes in texture and rheological properties, which next are running during the storage of a chilled or frozen product. These changes are significant enough for potential consumers to be made aware of the fact that the texture of the product changes considerably during its shelf life. Copyright © 2009 Society of Chemical Industry     

基于近红外光谱构建虹鳟鱼营养成分快速检测模型

目的 基于近红外光谱构建虹鳟鱼营养成分快速检测模型。方法 先采集200条虹鳟鱼近红外光谱数据,再用国标方法测定每条虹鳟鱼3种营养成分（水分、脂肪和蛋白质）的含量,将近红外光谱数据与营养成分数据一一对应,利用近红外光谱技术(near-infrared spectroscopy, NIR)结合偏最小二乘法(partial least squares, PLS)建立近红外快速检测模型,并筛选出最佳检测模型。结果 水分含量检测模型的预处理方法为多元散射校正(multiple scatter correction, MSC),波段为4000~10000 cm-1时,模型最优;脂肪含量检测模型预处理方法为标准正态变量变换(standard normal variable transformation, SNV),波段为5000~7144,7404~10000 cm-1时模型最优;蛋白质检测模型的预处理方法为二阶导数(ds2)+SNV+Savitzky-Golay平滑(sg9),波段为4100~5100,5400~9000 cm-1时模型最优,最优模型的Q值、校正模型相关系数(RC)、交互验证集相关系数(RP)均较大,校正集标准差(SEC)和预测集标准误差(SCP)互相接近,满足最佳建模原则。结论 使用未参与建模的预测集对最佳模型进行验证,跌出结果为预测值与真实值（国标方法测定值）的绝对偏差均不超过5.7%,说明该模型可用于虹鳟鱼3种营养成分的检测,可实现虹鳟鱼营养成分的无损、快速检测,节约检测成本,缩短检测周期。     

Migratory behaviour of adult fast-growing brown trout (Salmo trutta,L.) In relation to water flow in a regulated Norwegian river

The migration pattern of spawners of brown trout (Salmo trutta) in relation to water flow was analysed by radio-tracking in the regulated River Gudbrandsdalslågen, Norway. During the upstream spawning migration in the high flow period, trout (2–12 kg) were caught, tagged and released 15 km downstream of a fish ladder at the Hunderfossen waterfall. The released fish displayed a systematic and directional upstream movement to the outlet of the tunnel from the hydroelectricity plant. In autumn and winter there is a minimum water discharge of 20–2 m³/s on p.s. in the river between the dam and the outlet of the tunnel, which has a discharge of 200–300 m³/s. When the water flowing over the Hunderfossen dam decreased to 20 m³/s, the ascent of brown trout up the river stopped and fish periodically entered the power plant tunnel. To determine the flow necessary to attract fish into the spawning reach above the tunnel outlet, two experiments were undertaken using 12 and 17 radio-tagged trout. In the first experiment, 60 m³/s of water released for 24 h resulted in the migration of 50% of the trout up the river. The second experiment, releasing 60 m³/s for 24 h, followed by 30 m³/s for 24 h two days later, resulted in the migration of 60% of the trout. Only one fish ascended the river at a flow of 30 m³/s. It is recommended that a repeated release of water at 60 m³/s is made in periods of minimum water discharge to save the spawning migration. The results demonstrate the advantage of using radio-tracking in experiments dealing with fish migration in relation to water-flow management.     

Movement and growth indicators in resident and adfluvial coaster brook trout (Salvelinus fontinalis) in the Hurricane River,Lake Superior,Michigan, USA

Brook trout (Salvelinus fontinalis) are found throughout Lake Superior, Lake Nipigon, and their tributaries. Lacustrine and adfluvial life history variants were historically popular with anglers and were called coasters; coaster brook trout populations are now severely reduced and are of conservation concern. Coasters were known to grow larger and mature later than their stream resident counterparts. This study compared movement patterns, age, size, condition, and relative weight of wild coaster and resident brook trout from the Hurricane River, Pictured Rocks National Lakeshore, Michigan. Wild brook trout ≥ 100 mm from the Hurricane River downstream from Hurricane Falls were tagged with passive integrated transponder tags and monitored for stream-lake movement behavior from May 2003 to November 2007. During 2006 and 2007, brook trout were scale sampled and aged to construct a regression that was then used to calculate the age of all brook trout tagged from 2003 to 2007. Most brook trout movement took place in the fall with October the peak month of emigration with a secondary peak in late spring/early summer and some activity nearly year round. There were no differences found in age structure, size or condition between coasters and residents while in the stream. Our data suggest that a priori growth differences are not determining the expression of coaster outmigration and that stream-lake movements made by coasters, likely driven by habitat requirements, may be highly flexible and facultative.