Effect of handling and fish size on secondary changes in carbohydrate metabolism in Atlantic salmon, Salmo salar L.

Two size groups (0.5 and 3 kg) of Atlantic salmon, Salmo salar L., were stressed by netting and transport from sea cages into land-based tanks. Handling lasted for 1 h. Before onset of stress, basal concentrations of haematocrit and haemoglobin, plasma cortisol and glucose, and liver and muscle glycogen were measured. All levels were within ranges reported for salmon. After handling and at chosen time intervals during recovery, samples were taken to judge the impact of handling and whether secondary changes in carbohydrate metabolism were related of fish size. A low cortisol peak indicated a mild stress reaction after handling independent to fish size. Plasma glucose peaked as cortisol declined, and returned to basal levels within 48 h. Liver glycogen seemed to be the main source of plasma glucose. No changes were measured in muscle glycogen concentrations. The results indicate a high tolerance to handling stress in Atlantic salmon independent of fish size.     

The effects of stress and storage temperature on the colour and texture of pre-rigor filleted farmed cod (Gadus morhua L.)

This experiment deals with the effects of pre‐slaughter stress and storage temperature on muscle pH, fillet contraction, colour and texture in pre‐rigor filleted farmed cod fillets. The fish were either sedated with a low dose of MS‐222 (14.3 mg L^?1) (unstressed groups) or exposed to the air for 3 min (stressed groups) before being submerged in a benzocaine bath (150 g L^?1). The fish were then killed by a blow to the head, their gills cut, filleted and finally stored at either 4 or 20°C. The stressed groups had significantly lower pH values after slaughter (pH=7.0) than the unstressed groups (pH=7.3). This difference was maintained until post rigor for the fish stored at 4°C, but at 20°C it was immediately overshadowed by a decrease in pH caused by temperature‐dependent processes. The length contraction and changes in registered colour values were more pronounced at both the higher temperature and the higher level of pre‐slaughter stress. Again temperature dominated, but significant and consistent effects were registered from stress. No significant effects of stress on texture post rigor were observed. It is concluded that high storage temperature masks the majority of effects caused by pre‐slaughter stress on the measured variables. Stress management protocols, however, are important when the fillets are kept at the common storage temperature of 4°C.     

Bleeding of Farmed Atlantic Cod: Residual Blood,Color, and Quality Attributes of Pre- and Postrigor Fillets as Affected by Perimortem Stress and Different Bleeding Methods

The main objectives of the study were to (a) assess the effect of perimortem stress on blood drainage, (b) compare the efficiency of gill cutting and direct gutting as bleeding methods, and (c) compare pre- and postrigor filleting strategies for presence of residual blood in Atlantic cod fillets. Anesthetized cod had significantly higher drainage of blood compared to stressed fish. Nevertheless, the visual assessments of residual blood were not affected by stress or bleeding method. Some minor, but significant, differences between pre- and postrigor fillets were found. Stressed fish were initially less light in color than those unstressed, but after ice storage there was no noticeable difference. However, initially, the largest difference in fillet color was due to different bleeding methods. Fillets cut from fish subjected to gill cutting were lighter and less red in color than those bled by direct gutting. After 7 and 21 days of storage, the color differences observed in fresh and salted fillets, respectively, were mainly due to the different rigor status when they were filleted, indicating that fillets cut postrigor were superior to fillets cut prerigor. Prerigor filleting resulted in lower water holding capacity after ice storage in anesthetized, direct gutted cod.     

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.     

Preslaughter stress and subsequent effect on flesh quality in farmed cod

The aim of this study was to investigate the effect of prehandling stress on the flesh quality of Atlantic cod (Gadus morhua). In order to stress the animal, water was reduced in the tank before a total of 30 fish were caught five at a time using a dipnet and held for 3 min, causing stress by hypoxia. This fish was compared with a control group (n=30) of fish exposed to anaesthetics directly in the tank. All fish were killed by a percussive blow to the head and exsanguinated and stored on ice before flesh quality was measured. Immediately after death and after ice storage for 3 and 8 days, 10 fish per group were measured for muscle pH, texture, fillet gaping, colour, drip loss and cathepsin D. Handling stress resulted in an initial increased fillet lightness, drip loss and decreased fillet shear force, although these differences did level off during ice storage. Stress caused by handling resulted in earlier onset of rigour mortis as compared with the control group, which reached maximum rigour tensions within 26 and 36 h postmortem respectively. We conclude that handling before harvest results in reduced time before entering rigour. After 8 days of ice storage, no effect of handling stress was seen on the muscle pH, flesh colour, fillet shear force, gaping score, drip loss or cathepsin D activity.     

Impact of starvation and handling stress on rigor development and quality of Atlantic salmon (Salmon salar L)

Farmed Atlantic salmon (Salmo salar L) were fed to satiation or starved for 35 d, and subjected to acute pre-slaughter stress or careful handling before slaughtering. Rigor development, post-mortem energy metabolism and quality variations were analysed during 72 h cold storage. The body weight averaged 2.9 and 3.5 kg of the fed and starved salmon, respectively. The starved salmon had lower condition factor (0.99 vs. 1.11) and higher slaughter yield (92.6 vs. 87.5%), but the fat content was similar (11.8–12.9%) in the fed and starved salmon. The initial glycogen level was lower in the starved salmon (21 vs. 29 μmol g^− 1), whereas initial ATP levels (6.4–6.6 μmol g^− 1) were not affected by starvation. Pre-slaughter stress accelerated rigor development, stimulated lactate formation through post-mortem glycolysis, and increased the breakdown of ATP and CP. The effect of stress on rigor development was less pronounced in starved salmon, and a significant interaction was observed between nutritional status and stress. Rigor development was closely correlated to ATP breakdown, especially in fillets. Acute stress accelerated flesh softening during ice storage. After 72 h storage, the fillets of the starved salmon exposed to careful slaughter handling had the significantly firmest texture, whereas the most intense fillet colour was observed in the starved/stressed salmon. Liquid leakage from the muscle during cold storage was lower in the starved salmon, but pre-slaughter stress had no significant impact. It is concluded that a starvation period of five weeks can improve the resistant to acute stress prior to slaughtering of Atlantic salmon that in turn hampers rigor development.     

Vitamin C status and physiological response of the gilthead seabream, Sparus aurata L., to stressors associated with aquaculture

Gilthead seabream, Sparus aurata L., fed diets of equal vitamin C content were exposed to three different stressors–hyposalinity, shallow water and handling–and the effect of each on the internal homeostasis of the fish was evaluated. The individuals subjected to hyposaline stress exhibited no significant changes in plasma osmolality. Na⁺. Cl^- K⁺, glucose, protein and triglyceride concentrations. Hepatic glycogen content was significantly lower in the fish subjected to the lower salinity (12%o), while the red muscle glycogen was unaltered. Amongst the challenged individuals, tissue ascorbate content was not significantly altered. Shallow water stress significantly diminished the liver and red muscle glycogen content, and lowered the liver. kidney and spleen vitamin C concentrations in the stressed fish. No significant changes were recorded in the plasma glucose, protein and triglyceride concentrations. In response to handling stress, no significant differences were detected in any of the measured parameters, with the exception of plasma glucose levels and the splenic L-ascorbic acid and ascorbate-2-sulphate (vitamin C2) contents. The lack of existing standardization of both experimental designs and analytical methods made comparisons of the present data with the work of other authors difficult, thus highlighting the necessity of coordinated research in this field.     

Plasma lysozyme levels in sheatfish Silurus glanis (L.) subjected to stress and experimental infection with Edwardsiella tarda

Two experiments were conducted to assess plasma lysozyme levels, leucocrit and haematocrit in juvenile sheatfish (90–140 g) under experimentally induced stress and infection. Stress was provoked by random modification of environmental light for 15 min, 16 times a day with a halogen lamp (500 W) and by holding fish in a net for 3 min twice a day. In the first trial, repeated measuring of marked sheatfish showed a progressive significant decrease in plasma lysozyme level, a significant increase in leucocrit and a significant decrease in haematocrit. After a rest period of 1 week, only the leucocrit value was back to the prestress value. In the second trial, light‐induced stress did not lead to any variation in lysozyme, leucocrit or haematocrit values. However, after intraperitoneal injection of Edwardsiella tarda (7 × 10⁸ cfu), a strong increase in plasmatic lysozyme in both stressed and unstressed groups of sheatfish was observed. The increase was significant vs. prechallenge levels 3 and 6 days after contamination, but no significant difference was detected between stressed and unstressed fish, despite the strongest stress (light+handling stress) applied to the fish at the beginning of contamination. Decreases in haematocrit values were observed in both groups of fish. A clear increase in leucocrit appeared in unstressed fish, whereas stressed fish showed a significant decrease in leucocrit values. Condition factor was significantly decreased by all kinds of stress. There were no difference in mortality between stressed and unstressed groups.     

Effects of Long-Term Feed Deprivation on the Development of Rigor Mortis and Aspects of Muscle Quality in Live-Stored Mature Atlantic Cod (Gadus Morhua L.)

Fresh Atlantic cod is available in large amounts in Norway during the first 5 months of the year. Live-storage of cod may extend the marketing period of fresh cod products throughout the year. In addition, this concept makes pre-rigor processing possible. The main problem of keeping wild cod in captivity is that it does not easily accept formulated dry feed. The purpose of this study was, therefore, to investigate how long-term live-storage of mature Atlantic cod in the absence of feed (79 days) affects the onset and development of rigor mortis, as well as fillet quality by assessing hardness and water-holding capacity of the muscle, pH, protein, and water content. The results showed that starvation of Atlantic cod for 23 days reduces the pre-rigor time from 29 to 17 h. Further starvation did not decrease this period significantly, suggesting that live-stored cod deprived of feed for 79 days may still be industrially processed before the onset of rigor mortis. More than 51 days of starvation reduced protein concentration and increased water content of the muscle. After 51 days, the muscle texture was softer than in fish starved for a shorter period.     

Fish welfare and quality as affected by pre-slaughter and slaughter management

. A reliable assessment of animal welfare-suffering and of its impact on product quality requires a multidisciplinary approach that takes into account fish behaviour and the different biochemical and physiological processes involved. This might be done by the contemporary study of changes of indicators of brain function, endocrine responses, post mortem tissue biochemical processes and quality changes. This work reviewed some of the most used indices of stress at the time of slaughter, commercial slaughter methods and related stress effects on physical and biochemical parameters of fish quality. The set of the available data seemed to indicate that, although of some results appear contradictory, pre-slaughter and slaughter stressful practices could have an important effect on the flesh quality in fish. A clear effect emerged mostly on the physical properties of flesh, because severe stress at slaughter time exhausted muscular energies, produced more lactic acid, reduced muscular pH, increased the rate of rigor mortis onset. In this way they could have significant negative effects on technological traits, flesh quality and keeping quality of fish. Asphyxia and electrically stunned fish were more stressed than spiked, knocked and live chilled fish. Combining various methods together might be a more satisfactory strategy for both animal welfare and product quality.     

急性离水操作胁迫对四指马鲅(Eleutheronema tetradactylum)幼鱼组织结构和氧化应激的影响

为探究急性离水操作胁迫对四指马鲅(Eleutheronema tetradactylum)幼鱼组织结构和氧化应激的影响,本研究通过组织切片和酶活性测定来观察及检测鳃和肌肉显微结构的变化、抗氧化酶活性以及Na+-K+-ATP酶活性,以探究四指马鲅应激反应规律。结果显示,急性离水操作胁迫2 h后,鳃小片、扁平上皮细胞以及线粒体丰富细胞都出现不同程度的损伤;肌肉从肌纤维变性、肌纤维束之间的间隙增宽、空泡化至肌肉组织整体失去固有形态,并且呈逐渐分解的趋势;超氧化物歧化酶(SOD)和还原型谷胱甘肽(GSH)有相同的变化趋势,胁迫后的2 h显著下降(P<0.05),但12 h时则升至最高值。过氧化氢酶(CAT)和总抗氧化能力(T-AOC)水平在处理后2 h无显著变化(P>0.05),之后升高,直到12 h达到峰值。丙二醛(MDA)含量在胁迫后的2 h无显著差异(P>0.05),直到6 h达到峰值。SOD和CAT活性在处理24 h后显著低于处理前,其他酶变化不显著。Na+-K+-ATP酶活性在处理后2 h显著升高(P<0.05),12 h达到峰值,24 h恢复到处理前水平。本研究表明,操作胁迫会对鳃和肌肉的组织结构造成损伤,而且随时间持续,损伤呈现加重趋势;肌肉抗氧化酶系统在受到氧化压力2 h后才启动,处理后12 h肌肉受到的氧化压力最大,抗氧化酶活性最强;在受到外界刺激时,SOD和GSH之间可能存在协同作用;MDA可以作为四指马鲅氧化损伤的快速响应生物标记物。     

Fasting combined with long catch duration modifies the physio‐metabolic response and flesh quality of rainbow trout

Pre‐slaughter handling involves fasting fish and catching them, which can affect fish welfare and flesh quality, but few studies have considered their combined effects. In this study, adult rainbow trout (320 ± 10 g average weight) were fasted for 7 days (135.6 degree days) and subjected to a long catch duration (20 min), compared with controls (no fasting or short catch duration). Condition factor, organ weight indexes and carcass yield decreased with fasting but not catch duration. Plasma concentrations of cortisol, glucose and lactate increased after a long catch, while plasma triglycerides decreased with fasting. Liver glycogen concentration was lower in fasted fish, and liver luminosity and chroma were higher after fasting with a long catch. Regarding flesh quality, rigor mortis resolved more slowly and final muscle pH at 48 hr post‐mortem was higher for fasted fish with a long catch time. Muscle glycogen concentration was higher in fasted fish, where chroma was also lower. Fasted fish had lower lipid oxidation, but there were no differences in fat content in muscle. Fasted fish with a long catch duration also had less monounsaturated and more saturated fatty acids. In conclusion, a long catch triggered a stress response that had negative effects on flesh quality, independently of fasting.     

Cage‐cultured Largemouth Bronze Gudgeon,Coreius guichenoti: Biochemical Profile of Plasma and Physiological Response to Acute Handling Stress

We examined the blood biochemical profile and the physiological response to acute handling stress of a historically important economic but currently a rare endangered fish, Largemouth bronze gudgeon, Coreius guichenoti, in the upper Yangtze River. The results showed that the glucose (GLU) and triglyceride (TG) levels in the cage‐cultured C. guichenoti were significantly higher than those of the wild type, and the basal cortisol (COR) level was higher than that of most other fish species. In the stress experiment, the fish were subjected to a low‐ and high‐intensity handling stress, respectively, and sampling was performed before the stress and at 0, 1, 4, 12, 24, 72, 120, and 168 h after the stress. The levels of COR, GLU, lactate (LA), and alanine aminotransferase (ALT) of stressed fish exhibited an increase first and then a recovery to the pre‐stress levels with a typical acute stress response in the first 24 h. Fish in both stressed groups were spontaneously infected with Ichthyophthirius multifiliis from the 24th to the 168th h, and exhibited a chronic stress response. These data would facilitate the studies of blood physiology of C. guichenoti and related fish in health evaluation, species propagation and conservation, as well as the stress response in aquaculture.     

Bleeding of anaesthetized and exhausted Atlantic salmon: body cavity inspection and residual blood in pre‐rigor and smoked fillets as determined by various analytical methods

The bleeding efficiency of anaesthetized and exhausted Atlantic salmon was studied. Unbled fish were used as control groups for both treatments. Several analytical methods (computer vision, Minolta Chroma Meter, transflectance spectroscopy, haemoglobin iron and visual assessment of smoked fillets) were used to evaluate colour or residual blood contents of pre‐rigor and smoked fillets. In all cases, the amount of residual blood in the fillets was modest and blood was not considered a quality problem in terms of fillet appearance. Perimortem stress did not affect residual blood contents of pre‐rigor fillets. Only salting and smoking had a significant effect on filet colour. The low levels of residual blood was partly attributed to filleting shortly after killing allowing washing before the blood had time to coagulate. In addition, a computer vision method was developed for automated blood inspection of the body cavity after gutting and washing. A classifier (‘no blood’ or ‘blood present’) based on linear discriminant analysis was tested and the classification accuracy was over 90% as evaluated with the leave‐one‐out method.     

The response of coral trout (Plectropomus leopardus) to capture, handling and transport and shallow water stress

The stress response of coral trout (Plectropomus leopardus ) to wild capture or controlled shallow water stressors was investigated. Stress associated with capture from the wild, handling and transport and shallow water evoked significant changes in circulating levels of cortisol, glucose, lactate, haemoglobin (Hb) and haematocrit (Hct) in coral trout. Plasma glucose, Hb and Hct increased over 30 to 60 min in response to the controlled stressor and then returned toward unstressed levels, even if the stressor persisted. Cortisol increased to maximum levels over the 60 min following the onset of the stressor and remained elevated for 4 h in the case of a single 30 min shallow water event or 3 d in response to the capture, handling and transport. The difference between the responses of blood glucose and cortisol suggests that cortisol does not maintain blood glucose during stress in coral trout. The concentrations of circulating thrombocytes, lymphocytes and granulocytes were also significantly affected by shallow water stress. As lymphocytes and granulocytes are important immune components, reduced concentrations of these cells may explain the increases in disease susceptibility, commonly observed in stressed fish during live transport.     

Influence of sea ranching on hatchery-reared anadromous Arctic charr, Salvelinus alpinus (L.)

Anadromous Arctic charr, Salvelinus alpinus (L.), from the River Halselva in Finnmark, northern Norway, were used as broodstock for the production of smolts. During the smolting period the fish were either shielded from normal working routines, subjected to normal work routines, or exposed to excessive work routines (stress) within the hatchery. None of the handling routines affected the gill-Na-K-ATPase activity, or the hypoosmoregulatory capacity of the charr. Compared with normal handling, neither stress nor shielding caused any significant difference in the migratory behaviour of the charr, in the duration of the sea residence, or in homing success. However, the stressed group did show a lymphocytopenia at end of the rearing period.     

Evaluation of the Effects of Different Stunning Methods on the Stress Responses and Meat Quality of the Amazon hybrid surubim,Pseudoplatystoma fasciatum female × Leiarius marmoratus male

Different stunning methods (carbon dioxide [CO₂] and hypothermia) used in industrial fish processing were compared with asphyxia in air, which is used in traditional fishing, to evaluate the effects of these methods on the stress responses and the meat quality of the Amazon hybrid surubim, Pseudoplatystoma fasciatum female × Leiarius marmoratus male. After the application, blood and behavioral indicators were evaluated. Following death by gill cutting, the fish were gutted, and analyses of muscle pH, rigor mortis, the exudation of the meat, and coloration were performed. Significantly higher levels of cortisol and glucose were exhibited by the fish subjected to asphyxia than by the fish stunned by either CO₂ or hypothermia. The fish subjected to asphyxia displayed decreasing muscle pH during the first 2 h after death and showed higher rates of rigor mortis after 3 h than the fish that were stunned by the other two methods. The asphyxia is a practice that exposes fish to suffering by causing an increase in stress responses, which affects meat quality. The immersion of fish in water and ice (hypothermia) for 5 min was more effective stunning method than the use of CO₂, resulting in higher loss of sensibility and greater welfare.     

Determination of pH in Pre rigor Fish Muscle – Method Matters

ABSTRACT

The determination of post mortem muscle pH are often carried out in studies on how pre-slaughter handling influences the development of rigor mortis and the quality of the fish products. The analysis might be performed by inserting a pH-electrode into the intact flesh or using a suspension containing a minced muscle sample. Although it has been known for a long time that mincing muscle tissue accelerates glycolysis and breakdown of adenosine triphosphate (ATP), more recent studies quite commonly determine pH after mincing pre rigor muscle without including an enzyme inhibitor that arrests glycolysis. This may have resulted in anomalously low pre rigor muscle pH. The aim of the present work was to compare the two methods of pH determination in pre rigor fish muscle and to highlight the importance of including the enzyme inhibitor when homogenizing pre rigor fish muscle prior to pH analysis.     

Effect of blood glucose level on acute stress response of grass carp <Emphasis Type="Italic">Ctenopharyngodon idella</Emphasis>

Stress has a considerable impact on welfare and productivity of fish, and blood glucose level of fish may be a factor modulating stress response. This study evaluated the effect of blood glucose level and handling on acute stress response of grass carp Ctenopharyngodon idella. Fish were intraperitoneally injected with glucose at 0, 0.2, 0.5, and 1.0 mg g^?1 body mass (BM) and then were exposed to handling for 5 min. Glucose injection resulted in increase of plasma glucose level and liver glycogen content and decrease of plasma lactate level. Handling resulted in increase of plasma levels of cortisol, glucose, and lactate and plasma lactic dehydrogenase (LDH) activity and decrease of liver glycogen content. At 1 h post-stress, the plasma cortisol level was lower in the stressed fish injected with glucose at 0.5 mg g^?1 BM than the stressed fish injected with glucose at 0, 0.2, and 1.0 mg g^?1 BM. No significant differences were found in the activities of phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate kinase (PK) in the liver between the stressed and unstressed fish, regardless of the dose of glucose injection. At 1 h post-stress, the liver glucose-6-phosphatase (G6Pase) activity was higher in the fish without glucose injection than in the fish injected with glucose. This study reveals that blood glucose level can affect stress response of grass carp by modulating cortisol release and glucose homeostasis through glycogen metabolism and gluconeogenesis in the liver.     

Stress response of juvenile rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)to chemical cues released from stressed conspecifics

The objective of this study was to determine whether exposure of rainbow trout (Oncorhynchus mykiss) to water containing a stressed trout or skin extract from stressed and non-stressed trout would elicit a stress response in conspecifics. Juvenile rainbow trout were exposed for 1 hour to water containing a stressed fish, homogenized skin extracts from a non-stressed fish, skin extract from a stressed fish and water with none of these factors. The stress response was measured over a 24-h period (1, 6, 12, 24 h after exposure). Plasma cortisol levels increased at 12 h in fish exposed to water from a stressed fish and skin extract from a stressed fish. Plasma glucose and hepatic hsp70 levels were not affected by treatments. The results suggest that rainbow trout elicit a stress response when exposed to stress-related alarm cues released from conspecifics.