Maturity assignment based on histology‐validated macroscopic criteria: Tackling the stock decline of the Mediterranean swordfish (Xiphias gladius)

1. Effective stock assessment relies on the evaluation of the reproductive potential of a population, but this is often achieved using fast, inexpensive, and inaccurate macroscopic indicators of gonadal maturity. Indeed, this approach suffers from high error rates as a result of misclassification and operator errors. Although histology is considered the gold standard to assign reproductive stages, it represents a time‐consuming and expensive method. Therefore, cost‐effective approaches are currently needed to assess the species‐specific reproductive potential and define the correct size at first maturity (L₅₀).
2. In the present study a histology‐calibrated method based on the gonadal index (GI) was developed to assign maturity stages to the overfished Mediterranean swordfish (Xiphias gladius), supported by histological classification of gonadal development, an estimation of L₅₀, and an analysis of the reproductive output of this species.
3. The performance of this new method had an overall agreement of 90% with histological data, and the L₅₀ calculated by the GI‐based method compared with histology analysis was not statistically different (p > 0.05). Moreover, in order to apply this method without bias, a thorough validation of the relationship between length and gonad weight was carried out and the suitability of the GI to compare individuals of different size and maturity stages was confirmed.
4. The present findings provide a comprehensive picture of the patterns characterizing Mediterranean swordfish reproduction and a promising method to assign maturity stages based on a macroscopic indicator. This method has the potential to be extensively applied during routine fish sampling activities in the field because of its simple requirements.

     

Rapid Multiparameters Approach to Differentiate Fresh Skinless Sea Bass (Dicentrarchus labrax) Fillets from Frozen-Thawed Ones

Food authenticity is one of the major issues in the mind of today’s consumers. The sale of frozen-thawed fish fillets under the “fresh fillet” label is considered as a commercial fraud. However, their close sensory properties complicate the differentiation. This study focused on analyzing the composition of exudate (pressured flesh juice) in order to rapidly differentiate between fresh and frozen-thawed skinless fillets of sea bass (Dicentrarchus labrax). Protein concentration, α-D-glucosidase specific activity, nucleotides and related compounds (NRCs) concentration, and free calcium concentration were measured in exudates corresponding to fresh or frozen-thawed sea bass fillets. Significant increases of these four parameters were observed in exudates from frozen-thawed fillets, especially with a twofold increase in NRCs and free calcium concentrations. These results suggest that NRCs and free calcium concentrations can be promising indicators to rapidly detect mislabeling of fresh fillets.     

Detection of Frozen-Thawed Cycles for Frozen Tilapia (Oreochromis) Fillets Using Near Infrared Spectroscopy

Due to the ambient temperature fluctuation during the process of storage, transportation, and sale, frozen fillets may go through frozen-thawed cycles that result in quality changes. In order to detect the frozen-thawed cycles in frozen tilapia fillets, near infrared spectroscopy was applied. The thawing loss, cooking loss, moisture content, total volatile basic nitrogen, and texture profile of fillets in seven frozen-thawed cycles were analyzed to reflect the change of quality. A total of 60 fillets were used to collect the spectra on both dorsal and belly flesh in frozen and thawed state from the first to the seventh cycle. The results showed that there is a better discrimination among the once and the repeated frozen-thawed samples in the frozen state than the thawed state. Frozen samples were still conducive to the differentiation and had higher classification accuracy, ranging from 80% to 93.33%. Dorsal flesh was more beneficial for the differentiation than belly flesh and had the highest accuracy, ranging from 86.67% to 93.33% in the frozen state. These results showed that the nondestructive and fast detection of repeated frozen-thawed cycles in frozen tilapia fillets can be accomplished by near infrared spectroscopy, which has enormous potential for practical application.     

An oceanographic characterization of swordfish (Xiphias gladius) longline fishing grounds in the springtime subtropical North Pacific

During January–May, surface manifestation of multiple, individual basin‐scale fronts accentuate the central North Pacific Subtropical Frontal Zone (STFZ) system. The most prominent of these fronts are climatologically located at 32°?34°N and at 28°?30°N latitudes [herein nominally referred to as the ‘Subtropical Front’ (STF) and the ‘South Subtropical Front’ (SSTF), respectively], although considerable interannual variability in both position and intensity is observed. This seasonally dynamic system is also the region typically targeted by the Hawaii‐based swordfish (Xiphias gladius) longline fishing fleet, where the presence, position, and strength of the convergent fronts are believed to play a key role with regard to the catch and catch rates of swordfish. Information furnished by a recent series of meridional hydrographic surveys and concurrent satellite remote sensing data elucidate structural patterns and coupling of the physics and biology associated with these fronts. This enables a re‐characterization of the spring North Pacific STFZ and offers new insight into the seasonal variability of the phytoplankton dynamics in the subtropical North Pacific. On synoptic time scales, geographical positioning of the fronts may be systematically identified through surface outcropping of diagnostic thermohaline isopleths and therefore readily discerned from both shipboard surveys and by spaceborne sensors. The STF during spring can be characterized by the surface expression of the 34.8 isohaline and the 17°C isotherm within the frontal gradient. Biologically, the STF marks the transition from low chloropigment (chlorophyll + phaeopigments), nutrient‐depleted surface waters to the south to a more productive regime to the north. To the south, the 20°C and 35.0 surface isotherm and isohaline, respectively, are characteristically embedded in the thermohaline gradients associated with the SSTF. A sharp increase in depth‐integrated chloropigment is also observed at the SSTF and is ascribed to an increase in the concentration and thickness of the subsurface chloropigment maximum (SCM) prompted by the shoaling of the nutricline with the thermocline structure into the euphotic zone.     

Using Near Infrared Reflectance Spectroscopy (NIRS) to predict the protein and energy digestibility of lupin kernel meals when fed to rainbow trout,Oncorhynchus mykiss

This study examined the potential of using near infrared spectroscopy (NIRS) to predict the nutrient composition, energy density and the digestible protein and digestible energy values of lupin kernel meals when fed to rainbow trout. A series of 136 lupin kernel meals were assessed for their protein and energy digestibilities using the diet‐substitution approach in a series of 10 experiments over a 6‐year period from 2002 to 2008. Two reference diets were also included in each experiment. Minimal variance in the digestibility parameters of both reference diets was observed among the experiments ensuring that there was a high degree of robustness in the across‐experiment evaluations. The same lupin kernel meal samples were also scanned using a diode array near infrared spectrophotometer (DA‐NIRS). The spectra obtained by the DA‐NIRS were chemometrically calibrated against both the chemical composition and the digestible value data using multivariate analysis software. The cross validation tests used in this study provide a valid indication of the potential to predict the nutrient composition, energy value and digestible protein and energy values of the lupin kernel meals as used in diets for rainbow trout. That the standard errors of cross validation (SECV) of the parameters investigated were generally commensurate with the cross trial variation seen in the reference sample indicating robust calibrations for the two target parameters of digestible protein and digestible energy. Therefore this study demonstrates that within one raw material type that not only does significant variability in the digestible value of the raw materials exist, but that it is possible to use NIRS technology to provide rapid estimates of the digestible value of those raw materials in near real‐time.     

紫红笛鲷与红鳍笛鲷5种同工酶的比较研究

采用聚丙烯酰胺垂直平板梯度凝胶电泳的方法,对紫红笛鲷和红鳍笛鲷8种组织中的5种同工酶(EST,LDH,MDH,ME,POD)进行比较研究,对所研究的5种同工酶在两种鱼的组织分布、位点表达及活性作了分析和总结。试验结果表明:两种鱼的ME、MDH同工酶谱非常相似,只在活性上略有差异;EST、LDH、POD等的酶谱表达带型和活性不同,这些酶可作为紫红笛鲷和红鳍笛鲷的遗传鉴定标记,能够将亲缘关系很近的这两种鱼区分开来,从而为形态分类学提供生化依据。     

Chemical Composition of Fresh and Salted Lumpfish (Cyclopterus lumpus) Roe

The original "Eskimo" cardiovascular health benefit of omega-3 fatty acids was ascribed to EPA (eicosapentaenoic acid). The two readily available fish body oils (from U.S. menhaden and Japanese sardines) have approximately 180 mg of EPA/gram, accompanied by much less (120 mg) DHA (docosahexaenoic acid). The EPA was recognized as the source of a prostaglandin (PGI₃) acting as an agent to keep the vascular walls soft and flexible, thus hindering atherosclerosis and vascular constriction, but DHA presented a problem as no such role for it was known. Australian researchers identified DHA as preventing cardiac arrhythmia because they used tuna body oil (DHA ~5 x EPA) in their research. Generally our analyses of salmon muscle triglycerides seem to show DHA > EPA. Total salmon muscle lipids in fillets obtain extra DHA from phospholipids. In the United Kingdom an official medical body now recommends eating fish twice a week and "oily" fish once a week. Examination of DHA for a legitimate health claim in the cardiovascular system, and in infant neural developments and nutrition, and maternal nutrition, offers an alternative market exploiting the most recent developments. These matters should be investigated by the salmon aquaculture industry.     

Comparative Variations of Extractive Nitrogenous Components and Quality in Fresh Muscle and Dried Product of Rabbitfish (Siganus fuscescens) in Taiwan

ABSTRACT

Variations in the level of quality and extractive nitrogenous components were investigated in the fresh muscle and commercial dried products of rabbitfish Siganus fuscescens collected from Penghu, Taiwan. The respective freshness quality for fresh muscle is as follows: trimethylamine oxide (TMAO), 29.50 mg N/100 g; trimethylamine (TMA), 2.30 mg N/100 g; NH₃, 6.61 mg/100 g; total volatile basic nitrogen (TVBN), 13.32 mg/100 g; aerobic plate count, 1.53 log CFU/g; and K-value, 28.80%. The respective freshness quality for dried products is as follows: TMAO, 43.44 mg N/100 g; TMA, 25.56 mg N/100 g wet wt.; NH₃, 52.00 mg/100 g wet wt.; TVBN, 149.98 mg/100 g; aerobic plate count, 4.16 log CFU/g; and K-value, 89.73%. The major fatty acids in the fresh muscle and dried products are C16:0, C18:1 n-9, C18:0, C16:1 C22:6 n-3, and C22:5 n-3. The major nucleotide compound is inosine 5?-monophosphate (IMP) in the fresh muscle (68%) and hypoxanthine (Hx) in the dried products (79%). The level of total free amino acids in the dried products shows significant variation depending on the processing method of the plants.     

Comparison of Collagen Distribution and Muscle Structure Between Cultured Amberjack (Seriola dumerili) and Cultured Yellowtail (Seriola quinqueradiata)

ABSTRACT

The collagen distribution in cultured specimens of amberjack and yellowtail were assessed by histochemical observation in relation to the meat texture of the fish. Major structural alteration was observed in the level of pericellular connective tissue of yellowtail that had higher muscle lipid content; these changes are likely to be associated with the large-scale changes in muscle firmness resulting from the weakening of the cellular binding force. However, lipid deposition was limited to the myocommata in amberjack muscle; lipid deposition was not observed in the pericellular connective tissue, which is the likely reason why amberjack maintained firmer meat texture.     

Comparison of conventional and molecular techniques to investigate the intestinal microflora of rainbow trout (Oncorhynchus mykiss)

The concept of the use of probiotic organisms or prebiotic compounds to modify the fish gut microflora is becoming a popular topic for investigation. A major flaw in many such studies is a failure to consider fully the nature of the established microflora, which is to be modified pre-, or probiotically. Since it is widely accepted that a large proportion of bacteria are non-culturable, the use of conventional bacteriological (culture) techniques alone to investigate fish intestinal microflora may be expected to bias results. We report a study designed to investigate the normal intestinal microflora of rainbow trout (Oncorhynchus mykiss) using both conventional bacteriological and molecular methods.Over an 18 month period, the intestinal microflora of a single population of laboratory-raised rainbow trout was investigated. Bacteria isolated using bacteriological techniques were identified using the BiOLOG system and 16S rRNA gene sequencing. Dominant bacteria consistently were Aeromonas sp. and Carnobacterium piscicola, demonstrating that the microflora is stable in fish kept in defined conditions. Restriction Fragment Length Polymorphism (RFLP) and 16S rRNA gene sequence analysis was used to investigate anaerobic and non-culturable bacteria. An obligate anaerobe, Clostridium gasigenes, was shown to be among the dominating intestinal microflora.     

Histopathological changes and tissue residue concentrations of monosex Nile tilapia (Oreochromis niloticus,L) fries exposed to oxytetracycline

Aquaculture International - The current study evaluated the biosafety of oxytetracycline (OTC) exposure for 30 days in monosex Oreochromis niloticus fries. The fries were exposed to OTC...     

Settling velocity and total ammonia nitrogen leaching from commercial feed and faecal pellets of gilthead seabream (Sparus aurata L. 1758) and seabass (Dicentrarchus labrax L. 1758)

The physico-chemical characteristics of particulate wastes of Sparus aurata and Dicentrarchus labrax were investigated. Changes in the dimensions, settling velocity and total ammonia nitrogen (TAN) leached from commercial feed pellets were investigated after soaking. Also, the settling velocity and TAN leached from faecal pellets of these fish were assessed at 15 and 25 °C. The settling velocity of feed pellets was influenced positively by pellet weight and negatively by immersion length as a result of changes in pellet dimensions after soaking. The settling velocity of faecal pellets was determined by pellet weight. The experimental design did not allow identification of any consistent effect of water temperature on settling velocity. Total ammonia nitrogen leaching over time from feed and faecal pellets was successfully explained by means of a first-order kinetic equation. For feed pellets, water temperature significantly affected the speed of the process and the time at which the maximum TAN leached was reached, but did not influence the maximum TAN leached. Leaching was related to feed pellet size, and so the smaller the pellet, the higher the leaching. Total ammonia nitrogen leaching from faecal pellets was greater per unit weight than in feed pellets. However, neither water temperature nor fish species influenced TAN leaching from faeces.     

Secretion of hatching enzyme and its proteolytic activity in coregoninae (Coregonus albula L andC. lavaretus L) embryos

After the electrial stimulation Coregoninae embryos secreted the hatching enzyme (chorionase) within 0.1–0.5 h, and the dissolution of their chorions lasted 1.2–2.0 h, depending on embryo's developmental stage (DS 13 or DS 14) and water temperature (5.2 or 9.6–9.8°C).Crude chorionase (hatching liquid) ofCoregonus albula andC. lavaretus was collected in large quantities by means of the electric stimulation of eggs. In both species the temperature optimum of proteolytic activity of the crude chorionasc was 30°C; the activity was lost at temperatures < 3-2°C and > 35–40°C. The maximal proteolytic activity was observed at pH 8.5; a rapid decrease in enzyme activity was evident at pH < 7.0, and the activity was zero at pH 6.The temperature-activity curve of chorionase may reflect the adaptation of Coregoninae to hatching immediately after the ice cover recedes from lakes, whereas the rapid decrease of enzyme activity at pH 7 -pH 6 can affect adversely the process of hatching in acidified lakes.     

养殖日本真鲈和大口黑鲈原料特性比较

为了解养殖海水鲈鱼日本真鲈(Lateolabrax iaponcas)和淡水大口黑鲈(Micropterus salmoides)原料特性及加工可适性,测定了养殖日本真鲈和大口黑鲈的形态参数、基本成分、蛋白质组成、p H值、采肉率、熟肉率、系水力、滴水损失、鱼肉色泽和质构参数,并对养殖日本真鲈和大口黑鲈原料特性进行比较分析。结果表明:日本真鲈和大口黑鲈的形体参数和色泽差异显著(P0.05),两者的鱼头、鱼骨和内脏所占比例均较高;粗脂肪含量差异较大(P0.05),大口黑鲈粗脂肪含量是日本真鲈的2.70倍;粗蛋白总含量差异不大,但各种蛋白的含量有显著性差异(P0.05),日本真鲈的总基质蛋白含量高于大口黑鲈;大口黑鲈鱼肉较日本真鲈p H略低,熟肉率低,滴水损失率和失水率分别为日本真鲈的2.20倍和2.06倍;大口黑鲈和日本真鲈的质构参数均存在显著性差异(P0.05),大口黑鲈质构特性优于日本真鲈,口感较好。综合分析表明日本真鲈适合加工鱼糜等产品,而大口黑鲈适合生鱼片、鱼片等加工。两种鱼在加工过程中产生的下脚料较多,应合理利用下脚料提高其附加值。     

Comparison of Physical,Thermal and Chemical Methods to Measure Protein Denaturation in Frozen Pacific Whiting (Merluccius productus)

The potential of using the torsion test and differential scanning calorimetry (DSC) to determine the effect of frozen storage on protein denaturation in fish fillets was investigated. Pacific whiting fillets were stored for 12 weeks at three temperature conditions: -20¦C, -8¦C, and at a level varying between 0 and -8¦C. Salt soluble protein (SSP) extractability and Ca++-ATPase activity were used to evaluate the torsion test and DSC. The shear strain value of the torsion test provided a good correlation with SSP extractability, Ca++-ATPase activity, and myosin transition enthalpy as measured by DSC. Therefore, shear strain can be considered as a useful tool for the determination of protein denaturation in Pacific whiting during periods of frozen storage. Because Ca++-ATPase activity, shear stress and shear strain, and myosin transition enthalpy all decreased within one week, protein deterioration in frozen Pacific whiting appears to be rapid at the temperatures tested.     

Comparison of brown trout (Salmo trutta) reared in fresh water and sea water to freshwater rainbow trout (Oncorhynchus mykiss): II. Phosphorus balance

Brown trout and rainbow trout (average weight 100 g) were reared in fresh water at 12 °C under the same conditions before transferring brown trout to sea water, in order to compare phosphorus utilisation in both species. Apparent phosphorus availability, orthophosphate excretion and phosphorus accretion in the fish were directly determined. Thus, actual phosphorus mass balance was built. Rainbow trout raised in fresh water had a higher phosphorus retention coefficient (maximum 50 %) than brown trout reared in fresh water (maximum 45 %). Transferring brown trout to sea water induced a reduction in phosphorus retention (maximum 39 %). Orthophosphate excretion, ranging 7–20 mg phosphorus per kg wet weight per day, represented 10–20 % of ingested phosphorus. Phosphorus availability was lower in brown trout raised in sea water (65 %) than brown trout raised in fresh water (76 %). Phosphorus balance measurements showed that 90 to 98 % of phosphorus flow could be accounted for.     

Feasibility of using rare earth elements (REEs) to mark and identify escaped farmed Atlantic salmon Salmo salar L.

A series of rare earth elements (REEs) were evaluated as potential markers in scales of Atlantic salmon 1⁺ and 0⁺ smolt by addition of these elements to the feed. Chlorides of 5 REEs were tested, alone or in combination: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd) and dysprosium (Dy). The labelled‐diets contained 125 or 250 mg REE kg^?1 feed and were administered for up to 10 weeks. Fish scales were collected and analysed by inductively coupled plasma‐mass spectrometry (ICP‐MS) before start, 5 and 10 weeks after labelling started and finally 2 or 4 months after marking. The results demonstrated that the five tested elements were clearly incorporated into the scales of the fish fed the supplemented diets. Uptake and concentrations increased gradually during the feeding period, and no principal differences were found between the two smolt types. Combining 2 REEs in the same feed did not affect the incorporation of either of them. After a ‘dilution’‐period of 2–4 months the concentrations of all markers (except La) in the scales of the treated‐fish were still significantly higher than those of the untreated‐fish. The background concentrations of the tested markers and some other elements were also measured and found to give interesting information.     

软颗粒饲料与鲜杂鱼糜对大黄鱼养殖水质的影响

在水温18．0～21．0℃、盐度21．0～25．8下,给平均体质量为280．0 g／尾的大黄鱼投喂软颗粒饲料（试验组）和鲜杂鱼糜（对照组）,评价两种饲料对环境影响,其中试验组、对照组各设3个平行,空白组（不放鱼也不投料,仅有砂滤海水）不设平行。试验结果表明,试验组和对照组养殖水中总氮、总磷和化学需氧量含量均与空白组差异显著（P＜0．05）,对照组最高,空白组最低;试验组与对照组水中总磷差异不显著（P＞0．05）,而总氮和化学需氧量含量均差异显著（P＜0．05）;试验组水中沉积物总量显著少于对照组（P＜0．05）;试验组水中沉积物中总氮、总磷总量均显著少于对照组（P＜0．05）。软颗粒饲料对养殖环境的影响显著小于鲜杂鱼糜,可在海水鱼类网箱养殖中应用推广。     

三倍体与二倍体泥鳅的组织细胞学比较

为探明三倍体和二倍体泥鳅的组织细胞学差异，运用血液涂片及组织切片方法，对三倍体、二倍体泥鳅的红细胞及其细胞核的长轴和短轴，血液中血细胞的组成及仔鱼眼部构造等进行了比较。结果表明，三倍体泥鳅红细胞及其核的长轴均比二倍体的要大，其中前者红细胞核的长轴约为后者的1．12倍，红细胞体积、核体积分别约为后者的1．62和1．44倍。三倍体泥鳅红细胞的相对数量明显少于二倍体泥鳅，而嗜中性细胞、单核细胞及淋巴细胞则多于后者。此外，三倍体泥鳅眼部色素层细胞数量少于二倍体。