Quality improvement by vacuum treatment of boiled skipjack loins for the production of dried skipjack

ABSTRACT: This study attempted to reduce the lipid and water contents in boiled skipjack loins by vacuum treatment and the quality of vacuumed boiled meat was then evaluated during the chilled and frozen storage. The boiled meats were vacuumed at a pressure of 400 Pa for 30 min using a vacuum freeze dryer as an experimental convenience in order to degrease, cool and dehydrate rapidly. The vacuumed boiled meats were stored at 0.0 ± 0.2°C for 10 days and at −20 ± 0.5°C for 90 days. The unvacuumed boiled meats were cooled by air-cooling and stored as the control. Lipid content on a wet basis (w.b.) was reduced as much as 0.5% in the ventral part and 0.4% in the dorsal part of the boiled meats after vacuum treatment. Water content (w.b.) was reduced as much as 2.5% in the ventral part and 3.0% in the dorsal part. The thiobarbituric acid and volatile basic nitrogen values in vacuumed boiled meats were significantly lower ( P < 0.05) than that in unvacuumed boiled meats during storage. Inosine monophosphate (IMP) was only detected as a major nucleotide (about 70%) in boiled meats, and the decomposition of IMP in vacuumed boiled meats was smaller than that in unvacuumed boiled meats during storage. It was concluded that the quality of boiled skipjack loins could be improved by vacuum treatment as a preprocessing procedure in the production of dried skipjack such as katsuobushi .     

Fortification of <Emphasis Type="Italic">niboshi</Emphasis> with histidine prepared from <Emphasis Type="Italic">katsuobushi</Emphasis> protein digest

ABSTRACT:   Free and total histidine contents in the muscle of various fishes and invertebrates caught in the Seto Inland Sea were estimated. These contents were higher in the muscles from skipjack, yellowfin tuna, yellowtail and mackerel than in those from lizard fish, sea bream and hairtail. Invertebrate muscles, except squid, contained low free and total histidine. Boiled and dried anchovy ( niboshi ) contained lower free histidine than that of dried anchovy (suboshi). To prepare free histidine-rich extracts, the waste residue of soup stock from smoke-dried and shaved skipjack ( katsuobushi ) was digested with proteases. The extract of the enzyme digest contained high free histidine and was used to fortify niboshi with free histidine. If taken, the fortified niboshi may suppress food intake, and prevent obesity.     

Preventive method of color deterioration of yellowtail dark muscle during frozen storage and post thawing

ABSTRACT:   The aim of this study was to develop a practical preventive method for color deterioration of sliced or filleted yellowtail muscle, especially of dark muscle, during frozen storage and post thawing. When the sliced meats were packaged in a vacuum with low oxygen permeable flexible films and then stored frozen below −40°C, no significant discoloration or browning of dark muscle was observed for 9 months or more. For higher temperature storage at −20°C or −30°C, nitrogen gas substituted packaging was a useful practical method for storing sliced meats for 6 weeks. In order to prevent color deterioration of sliced meats after thawing and subsequent storage at 0°C, the efficacy of materials of packaging was investigated. The most desirable result was obtained by using a film with oxygen permeability of 50–90 cm³/m² per 24 h.     

Lipid peroxidation-derived hepatotoxic aldehydes, 4-hydroxy-2E-hexenal in smoked fish meat products

ABSTRACT:   Contents of 4-hydroxy-2 E -hexenal (HHE), hepatotoxic aldehydes, in smoked fish meat products (smoked salmon and fish meat sausage) were analyzed. Large differences in these contents between the different samples were observed. Very low levels of HHE were detected in fish meat sausage samples. However, a high level of HHE was observed in one batch of smoked salmon. Changes of HHE contents in yellowtail meat containing cherry and sugi wood vinegar stored at 0°C were also analyzed for 7 days. Malonaldehyde (MA) was also analyzed in these samples as an index of the lipid peroxidation level. After 3 or 7 days of storage, HHE contents in both wood vinegar-added samples were significantly higher, but MA contents were significantly lower than those of the control.     

Control of lipid oxidation and meat color deterioration in skipjack tuna muscle during ice storage

The present study investigated the effects of lipid oxidation on quality deterioration in the ordinary and dark muscles of skipjack tuna Katuwonus pelamis during the early stages of ice storage for 72 h. The lipid hydroperoxide content of the dark muscle was significantly higher (P < 0.01) than that of the ordinary muscle throughout 72 h of ice storage. The metmyoglobin content of the ordinary muscle gradually increased, and was accompanied with darkening in the fish meat color. On the other hand, the addition of sodium ascorbate or 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox^®) to the ordinary muscle of skipjack tuna significantly inhibited the formation of lipid hydroperoxide as well as metmyoglobin formation. Thus, a decrease in α-tocopherol content in the ordinary muscle with antioxidant addition was not observed during ice storage period. In conclusion, the rate of lipid oxidation of skipjack tuna ordinary muscle is closely related to metmyoglobin formation, and the addition of antioxidants to fish meat is effective at inhibiting lipid oxidation as well as myoglobin oxidation in post-mortem meat.     

Lipid class and fatty acid composition of phospholipids from the gonads of skipjack tuna

ABSTRACT:   Lipid class and fatty acid composition of phospholipids from the gonads of skipjack tuna were examined to evaluate effective utilization of the processing of by-products. The predominant phospholipids in the ovaries were phosphatidylcholine (PC; 47.9%), phosphatidylethanolamine (PE; 19.3%) and lyso-phosphatidylcholine (LPC; 19.1%). In contrast, those in the testes were PC (40.1%), PE (29.3%) and phosphatidylserine (PS; 9.6%). The percentage of docosahexaenoic acid (DHA) was markedly high at more than 50% in LPC of the ovaries, and PE and PS of the testes were also high. The percentages of DHA at sn-position 2 of the predominant phospholipids, except for PC in the testes, were more than 60%, in particular PE in the testes was remarkably high at 81.9%. After storage for 2 days at 5°C, the LPC content in the ovaries increased twofold and the DHA level of LPC was the same as before, though the contents of other phospholipids decreased.     

Size-related changes in habitat selection by larval grayling (Thymallus thymallus L.)

Abstract  – In a medium-sized river in northern Finland, larval grayling shifted with growth from shallow habitats with slow velocities, fine substrata and abundant vegetation cover to deeper sites with swifter velocities, coarse substrata and sparse vegetation cover within 3 weeks. Small (17–21 mm) larvae preferred water depths 10–30 cm, substrata dominated by mud or sand (<2 mm), 10–70% vegetation cover and water velocities <10 cm · s⁻¹. Middle-sized (22–25 mm) larvae preferred 30–90 cm depths, sandy substrata, <40% vegetation cover and velocities <10 cm · s⁻¹. Large (26–31 mm) larvae preferred >50 cm depths, substrata dominated by sand or boulders, <20% vegetation cover and 10–50 cm · s⁻¹ velocities. The strict habitat requirements of the smallest larval group suggest that these habitats, in particular, are important to the early survival of grayling.     

A study of delayed capture mortality syndrome in skipjack tuna, Katsuwonus pelamis (1).

Abstract. This study was initiated to determine the cause(s) of delayed mortality in newly captured skipjack tuna, Katsuwonus pelamis (L.), being held at the National Marine Fisheries Service Kewalo Research Facility. Sixty-four per cent of 244 skipjack tuna delivered to the facility died, usually on the second or third day after capture. The capture history, morphological data, serum chemistry (21 standard parameters), haematology, and histological samples of major organs, were obtained from 30 fish sampled at sea immediately after capture, or after approximately 4, 9, 24, 48 or 500+ h in captivity. The cause(s) of death in these fish could not be attributed to anoxia, disseminated intravascular coagulation, lactic acidosis, capture myopathy or infection. Post-capture haemodilution is hypothesized as a major factor of delayed capture mortality syndrome in skipjack tuna.     

Comparison of the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (T. obesus) tuna associated with drifting FADs in the equatorial central Pacific Ocean

We evaluated the behavior of skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye tuna (T. obesus) associated with drifting fish aggregating devices (FADs) in the equatorial central Pacific Ocean. A total of 30 skipjack [34.5–65.0 cm in fork length (FL)], 43 yellowfin (31.6–93.5 cm FL) and 32 bigeye tuna (33.5–85.5 cm FL) were tagged with coded transmitters and released near two drifting FADs. At one of the two FADs, we successfully monitored the behavior of all three species simultaneously. Several individuals remained around the same FAD for 10 or more days. Occasional excursions from the FAD were observed for all three species, some of which occurred concurrently for multiple individuals. The detection rate was higher during the daytime than the nighttime for all the species, and the detection rate for bigeye tuna was higher than for yellowfin or skipjack tuna. The swimming depth was deeper during the daytime than nighttime for all species. The fish usually remained shallower than 100 m, but occasionally dived to around 150 m or deeper, most often for bigeye and yellowfin tuna during the daytime. The swimming depth for skipjack tuna was shallower than that for bigeye and yellowfin tuna, although the difference was not large, and is probably not sufficient to allow the selective harvest of skipjack and yellowfin tuna by the purse seine fishery. From the detection rate of the signals, bigeye tuna is considered to be more vulnerable to the FAD sets than yellowfin and skipjack tuna.     

Dietary cholesterol and lecithin have limited effects on growth and body composition of hybrid striped bass (Morone chrysops × M. saxatilis)

The effects of cholesterol and lecithin on growth and body composition of juvenile hybrid striped bass ( Morone chrysops  ×  M. saxatilis ) were investigated by feeding juvenile hybrids (initial weight 5.0 g) diets containing cholesterol at either 0 or 1% and lecithin at either 0, 2, 4, or 6% in a 2 × 4 factorial design. Each of the eight diets was fed to fish in triplicate 38-L aquaria maintained as a brackish water recirculating system for 8 weeks. Weight gain, feed efficiency, muscle ratio and hepatosomatic index were not significantly ( P  > 0.05) affected by dietary supplementation of cholesterol or lecithin. Supplementation of the diet with lecithin at 4 and 6% significantly ( P  < 0.05) decreased intraperitoneal fat accumulation regardless of dietary cholesterol level. Neither muscle nor liver lipid levels were significantly altered by dietary supplementation of cholesterol or lecithin although both liver and plasma lipid classes were affected. Dietary cholesterol decreased concentrations of liver and plasma free fatty acids and liver phospholipids while increasing concentrations of liver triglycerides and plasma phospholipids. Dietary lecithin did not consistently affect plasma and liver lipid classes although changes in phospholipid levels approaching significance ( P =0.0502 and P =0.0513, respectively) were observed. Thus it is concluded that dietary supplementation with cholesterol or lecithin had no substantial beneficial effects on growth or body composition of juvenile hybrid striped bass.     

Rheological properties and structural changes in steamed and boiled abalone meat

ABSTRACT: Changes in tissue structures, rheological properties, and water content of abalone meat were studied in relation to boiling and steaming time. The adductor muscle of abalone Haliotis discus, which was removed directly from the shell, was boiled or steamed for 1 h, 2 h, and 3 h. When observed under a light microscope and by scanning electron microscopy, structural changes in the myofibrils were greatest in the boiled abalone meat compared with the steamed meat. When heating time was increased from 1 h to 3 h, the instantaneous modulus E ₀ of boiled abalone meat decreased gradually with increased heating time, whereas the E ₀ of steamed abalone meat was reduced when heated for 2 h. When heated for 1 h, the relaxation time of steamed abalone meat was much longer than that of boiled meat. There were no significant changes in the relaxation time of abalone meat among the different boiling times, but the relaxation time of steamed abalone meat was reduced gradually with increasing heating times. The study's results confirmed that the difference in rheological properties between the boiled and steamed meats was due mainly to the denaturation level of myofibrils when heated for 1 h, as well as due to the changes in water and solid content and the manner in which the inner water was exchanged after heating time was increased from 1 h to 3 h.     

Operational oceanography applied to skipjack tuna (Katsuwonus pelamis) habitat monitoring and fishing in south‐western Atlantic

Skipjack tuna (Katsuwonus pelamis) ranks third among marine resources that sustain global fisheries. This study delimits the spatiotemporal habitat of the species in the south‐western Atlantic Ocean, based on operational oceanography. We used generalized additive models (GAMs) and catch data from six pole‐and‐line fishing vessels operating during 2014 and 2015 fishing seasons to assess the effect of environmental variables on catch. We also analysed Modis sensor images of sea surface temperature (SST) and surface chlorophyll‐α concentration (SCC) to describe fishing ground characteristics in time and space. Catch was positively related to thermocline depth (24–45 m), SST (22–24.5°C), SCC (0.08–0.14 mg/m³) and salinity (34.9–35.8). Through SST images, we identified that thermal fronts were the main surface feature associated with a higher probability to find skipjack. Also, we state that skipjack fishery is tightly related to shelf break because bottom topography drives the position of fronts in this area. Ocean colour fronts and plankton enrichment were important proxies, accessible through SCC, used to delineate skipjack fishing grounds. Catch per unit effort (CPUE) was higher towards summer (median 14 t/fishing day) due to the oceanographic characteristics of the southern region. High productivity in this sector of the Brazilian coast defines the main skipjack feeding areas and, as a consequence, the greatest abundance and availability for fishing.     

Proximate composition of some north-eastern Pacific forage fish species

To understand the relative dietary value of forage fish as prey in the Bering Sea and Gulf of Alaska, whole organisms of 13 species were analysed for proximate composition (protein, oil, ash and moisture content). Eulachon ( Thaleichthys pacificus ) were high in oil (total lipid) (16.8% to 21.4%) and low in moisture (64.6% to 70.8%). Oil in capelin ( Mallotus villosus ) ranged from 2.1% to 14.0%. Juveniles of walleye pollock ( Theragra chalcogramma ), Atka mackerel ( Pleurogrammus monopterygius ), Pacific herring ( Clupea pallasii ), and prowfish ( Zaprora silenus ) had low oil contents (< 1.8%) and high moisture contents (> 80.3%). Rankings of median proximate values illustrate the similarities. Surf smelt ( Hypomesus pretiosus ), rainbow smelt ( Osmerus mordax ), pricklebacks ( Lumpenus spp.), Atka mackerel, Pacific sand lance ( Ammodytes hexapterus ) and Pacific sandfish ( Trichodon trichodon ) ranked high in median protein content (> 15.4%). Median ash content for all species ranged from 0.6% to 3.3%. Total wet mass caloric content (kcal g^–1) was calculated for the four main species and a linear model was developed for caloric content as a function of moisture. The linear models (caloric content = b₀ + b₁ × moisture) were Pacific sand lance and Pacific sandfish (b₀ = 7.82, b₁ = – 0.09); eulachon (b₀ = 7.97, b₁ = – 0.08); and capelin (b₀ = 9.70, b₁ = – 0.11).     

Phospholipase A<Subscript>1</Subscript> activity of crude enzyme extracted from the ovaries of skipjack tuna

The phospholipid class composition, fatty acid composition and phospholipase A₁ (PLA₁) activity from the ovaries of skipjack tuna were compared with those of six other species of marine fish. In the skipjack ovaries, the lysophosphatidylcholine (LPC) proportion for the phospholipid, the docosahexaenoic acid (DHA) percentage for the total fatty acids of the phospholipids and the PLA₁ activity of the crude enzyme were the highest among those of the seven species. The optimum pH and temperature for the PLA₁ activity of the crude enzyme from the skipjack ovaries were in the range of pH 6–7 and 20–30°C, respectively, and calcium ions were not required. As a substrate, phosphatidylcholine was more easily hydrolyzed than phosphatidylethanolamine by this enzyme, and the plasmalogen-type phospholipid was much lower than the acyl-type phospholipid. After a 6-h hydrolysis reaction of the purified phospholipid extracted from the mixed ovaries of skipjack and yellowfin tuna by this enzyme, the LPC ratio of the phospholipid increased from 20 to 72.6% and the percentage of DHA for the total fatty acids of the phospholipid also increased. Thus, skipjack ovaries might possibly be used as a source of PLA₁.     

Quality characteristics in raw and smoked fillets of Atlantic salmon, Salmo salar, fed high-energy diets

Atlantic salmon, Salmo salar , were fed four levels of dietary fat (256, 308, 346 and 389 g kg⁻¹ of diet) for 138 days, with the purpose of studying quality characteristics in raw and smoked fish fillets. Dietary fat levels up to 346 g kg⁻¹ resulted in increased fat content of the raw fillets. The dietary fat levels had a less systematic effect on perceived fatness of the smoked fillets and caused a trend towards better odour and flavour. The fat content of raw fillets was significantly ( P ≤ 0.05) correlated to lower smoke odour, greater rancid flavour, fatness, and a yellower hue of the smoked fillets. Astaxanthin levels of the raw fillets varied between 6 and 11 mg kg⁻¹ of fillet and were significantly ( P ≤ 0.05) correlated with greater intensity of smoke odour, lower off-odour, and less whiteness, greater colour intensity and a redder hue of the smoked fish. It is proposed that salmon fillets can be graded according to weight, fat content and colour values prior to smoking to obtain more standardized quality characteristics of the final product after processing.     

Effect of dietary carbohydrates and lipids on growth in cachama (Piaractus brachypomus)

The effects of diets with three contents of carbohydrates and lipids were evaluated on the growing performance of cachama Piaractus brachypomus juveniles (initial weight 7.8 ± 0.49 g). The experiments were performed a 3 × 3 factorial design (200, 280 and 360 g of carbohydrates and 40, 80 and 120 g of lipids kg^?1). Protein content was kept constant in 320 g kg^?1 and digestible energy between 11.3 and 16.1 MJ kg^?1. Simple effects and interaction of factors on growth performance varied significantly (P < 0.05) indicating dependence among them. The maximum weight gain was observed in fish fed 200 and 280 g kg^?1 carbohydrates and 40 g kg^?1 lipids. Increase of lipids from 80 to 120 g kg^?1 reduced growth significantly. Protein efficiency rate and percentages of protein retention and energy were positively correlated with carbohydrate levels and no significant differences (P > 0.05) were observed with the lipid levels. Results indicate that cachama utilizes carbohydrates as energy source more efficiently than lipids; likewise, lipid levels over 40 g kg^?1 depress growth at any carbohydrates level.     

Habitat characteristics of skipjack tuna (Katsuwonus pelamis) in the western North Pacific: a remote sensing perspective

Skipjack tuna habitat in the western North Pacific was studied from satellite remotely sensed environment and catch data, using generalized additive models and geographic information systems. Weekly resolved remotely sensed sea surface temperature, surface chlorophyll, sea surface height anomalies and eddy kinetic energy data were used for the year 2004. Fifteen generalized additive models were constructed with skipjack catch per unit effort as a response variable, and sea surface temperature, sea surface height anomalies and eddy kinetic energy as model covariates to assess the effect of environment on catch per unit effort (skipjack tuna abundance). Model selection was based on significance of model terms, reduction in Akaike’s Information Criterion, and increase in cumulative deviance explained. The model selected was used to predict skipjack tuna catch per unit effort using monthly resolved environmental data for assessing model performance and to visualize the basin scale distribution of skipjack tuna habitat. Predicted values were validated using a linear model. Based on the four‐parameter model, skipjack tuna habitat selection was significantly (P < 0.01) influenced by sea surface temperatures ranging from 20.5 to 26°C, relatively oligotrophic waters (surface chlorophyll 0.08–0.18, 0.22–0.27 and 0.3–0.37 mg m^?3), zero to positive anomalies (surface height anomalies 0–50 cm), and low to moderate eddy kinetic energy (0–200 and 700–2500 cm² s^–2). Predicted catch per unit effort showed a trend consistent with the north–south migration of skipjack tuna. Validation of predicted catch per unit effort with that observed, pooled monthly, was significant (P < 0.01, r² = 0.64). Sea surface temperature explained the highest deviance in generalized additive models and was therefore considered the best habitat predictor.     

中西太平洋鲣卵巢发育特征

根据2007年10月-2008年1月在中西太平洋采集的140个卵巢样本,利用组织学分析方法,研究了鲣卵巢的发育过程,详细描述了鲣卵巢、卵细胞的发育阶段。结果表明:(1) 组织学上,鲣的卵细胞发育过程分为6个时相,与之对应的,卵巢发育过程分为6个时期。(2) 鲣属于不同步产卵类型,卵巢内会同时出现不同时相的卵细胞。(3) 传统鉴定方法用于鲣卵巢发育状况时,存在不足之处,与组织学分析的结果差别较大,尤其是Ⅵ期的差别最大。(4) 调查海域的鲣至少有两个产卵高峰期,一个高峰期是11月底(12月初),另一个高峰期是12月底(1月初)。     

Response of African Catfish, Clarias gariepinus, to Different Dietary Protein and Lipid Levels in Practical Diets

This study was conducted to find the optimum level of dietary protein and lipid that could produce the highest growth, best feed utilization, and body composition of African catfish, Clarias gariepinus (9.5–10.3 g). Nine diets (three protein levels × three lipid levels) containing 25, 30, or 35% crude protein (CP) with 6, 9, and 12% lipids were formulated. Fish were fed one of the tested diets at the rate of 5% of body weight for the first 8 wk and 3% for the rest of the study. Diets were offered 6 d a week, twice a day (900 and 1400 h) for 13 wk. Fish growth increased significantly with increasing either protein or lipid levels, and the maximum growth was obtained in fish fed diets containing 30% CP with 12% lipid or 35% CP with 9% lipid. The lowest fish growth was obtained at 25% CP with 6% lipid. The optimum feed intake, feed conversion ratio, energy utilization, protein efficiency ratio, and protein growth rate were also recognized in fish fed the above diets. No significant differences in moisture and ash contents in fish fed diets containing different protein and lipid levels were recorded. The protein and lipid contents in the fish body tended to increase with increasing protein and lipid levels in diets. However, the higher protein contents were obtained in fish fed diets containing 35% CP with 6 or 9% lipid, while the lowest ones were obtained at 25% CP with 6 or 9% lipid. The higher lipid contents were obtained at 30 or 35% CP with 12% lipid, while the lowest ones were obtained at 25 or 35% CP with 6% lipid. The present study indicates that the increase of dietary lipid level has a protein-sparing effect, and the diet containing 30% CP with 12% lipid would be suitable for the optimum growth and effective protein utilization of fingerling African catfish.     

基于点格局的中西太平洋金枪鱼围网中鲣的空间格局特征

中西太平洋海域10°N~10°S是我国金枪鱼围网渔业的主要生产海域,本研究采用点格局分析方法对自由群鲣(Katsuwonus pelamis)和随附群鲣的空间格局特征进行分析。根据我国渔业公司2015年23艘围网渔船的渔捞日志数据,采用点格局分析方法的单变量函数配对相关函数g(r)、交叉相关函数J12(r)和标记相关函数kmm(r)对不同集群(自由群和随附群)的鲣资源的空间分布格局及竞争关系进行了研究。发现围网自由群和随附群点事件的空间分布上都是非均质的,表现为聚集性;自由群在1.9°~2.3°尺度下表现出随机分布格局。表明热带太平洋鲣在生命史的两个不同阶段,空间格局为相互吸引的集聚式分布特征,其原因在于中西太平洋鲣喜好生活于高温低盐的暖池东侧水域,且有永久收敛的表层水团和盐度锋面能够提供鲣群所需的生物饵料;出现随机分布的原因为这个海域的饵料生物分布的斑块状和不可持续性,鲣高度洄游特性能够保证其跟随饵料迁徙。在0°~0.35°尺度下,自由群和随附群的关系为竞争关系;当空间尺度超过0.35°后,随着尺度增大,两者关系为随机性关系。在随附群在空间尺度超过0.8°后,CPUE之间表现为正相关,有相对较弱的聚集热点和冷点区域,其他各尺度上CPUE为随机关系;自由群的CPUE在各尺度上都表现为随机关系。总之,自由群鲣和随附群鲣的空间格局在小尺度下表现为排斥竞争关系,在较大尺度下为独立的随机关系,其竞争关系主要为食物的有限性导致。