Evaluation of Quality Parameters in the Meat of Pintado Amazônico,Female Pseudoplatystoma fasciatum × Male Leiarius marmoratus,Subjected to Different Slaughter Methods

The objective of this study was to check the effect of different stunning methods on the meat quality of Pintado Amazônico, female Pseudoplatystoma fasciatum × male Leiarius marmoratus, stored on ice for 18 d. A total of 90 specimens (2.5 ± 0.45 kg and 58.21 ± 6.20 cm) were divided into three groups and subjected to stunning by: water saturated with CO₂, hypothermia on ice, or asphyxia in air. Subsequently, samples were removed to be analyzed after (times) 0, 2, 4, 6, 8, 10, 12, 14, 16, and 18 d. At the established times, aerobic mesophilic heterotrophic microorganisms and aerobic psychrotrophic heterotrophic microorganisms were quantified, and the pH, total volatile base nitrogen, color (L*a*b*), and sensory traits were analyzed. The stunning method significantly affected (P < 0.05) the meat quality. The group stunned on ice showed the best results compared with the other treatments.     

Effect of electrical stunning at slaughter on the carcass, flesh and eating quality of farmed sea bass (Dicentrarchus labrax)

Food quality aspects of farmed sea bass (Dicentrarchus labrax) were compared following two methods of slaughter: the normal commercial method of killing, by immersion in an ice slurry, or by first electrically stunning the fish, before immersion in an ice slurry. Quality was assessed for up to 10 days of storage on ice after slaughter. No differences were found between the slaughter methods in terms of an overall sensory evaluation of cooked fillets, or in terms of overall carcass quality: overall appearance, internal and external haemorrhage, fin damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. Using objective measurements of colour, no differences between fish from either treatment were found in terms of external colour or colour of the fillets. A chemical analysis of flesh nucleotide breakdown products as well as the freshness indicator K_i value did not differentiate the two treatments nor did the industry standard freshness scoring technique (QIM, quality index method), over 10 days of storage on ice. Flesh pH was marginally lower in electrically stunned fish at 4 h post mortem (6.42 cf 6.56) but by 24 h, pH in fish from both treatments had decreased to a similar level (6.22). Humane electrical stunning of sea bass at slaughter neither measurably improved nor decreased product quality for between 1 and 10 days of storage on ice. Electrical stunning accelerated the pattern of onset and resolution of rigor mortis. If electrical stunning were to be widely adopted, re‐education of buyers would be necessary as rigor mortis is currently used by buyers as a proxy measure of fish freshness.     

Slaughtering method and dietary α-tocopheryl acetate supplementation affect rigor mortis and fillet shelf-life of turbot Scophthalmus maximus L.

The effects of dietary α‐tocopheryl acetate supplementation and different slaughtering methods were investigated on the flesh quality of farmed market‐size turbot Scophthalmus maximus (L). Turbot were divided into three groups and fed commercial diets, supplemented with different levels of α‐tocopheryl acetate at the following dietary inclusion levels: 72 (100), 547 (500), 969 (1000) (mg of α‐tocopheryl acetate kg^?1 diet, analytical values with diet codes in brackets). After 5 months, fish (mean weight 1056 ± 19.7 g) from each dietary treatment were sampled, applying three different slaughtering methods: (A) bleeding in ice water; (B) thermal shock, no bleeding; (C) percussion followed by bleeding in ice water. The time course of rigor mortis was evaluated, using pH, rigor index and mechanical compression tests. The results showed that the three parameters corresponded very well. Percussive stunning resulted in higher initial post‐mortem pH (P < 0.01) and a significantly delayed onset of rigor mortis (P < 0.05). Diet significantly affected shelf‐life, with fillets from fish fed diets 500 and 1000 having lower TBARS (thiobarbituric acid reactive substances) numbers from day 2 (P < 0.001) and less colour deterioration from day 7 of storage on ice onwards (P < 0.05). These results suggest that an increase in dietary α‐tocopheryl acetate before slaughter as well as careful selection of the slaughtering method may greatly enhance the flesh quality of market‐size turbot.     

Preslaughter Anesthesia with Lippia alba Essential Oil Delays the Spoilage of Chilled Rhamdia quelen

This study evaluated whether anesthesia with essential oil (EO) of Lippia alba (300 mg L^?1 for 4 min) prior to electronarcosis (128 V m^?1 × 300 Hz for 5 s) or hypothermia (ice/water slurry) could delay fish spoilage during chilled storage of whole fish. Silver catfish (Rhamdia quelen) were subjected to two different pre-stunning treatments (water or anesthesia with EO of L. alba) followed by two different stunning procedures (hypothermia or electrical stunning), yielding four groups (n = 32/group): water (control) + hypothermia, water (control) + electrical stunning, EO of L. alba + hypothermia, and EO of L. alba + electrical stunning. After stunning, fish were slaughtered by percussion and stored in ice. Preslaughter anesthesia with the EO of L. alba extended fish shelf life by delaying the loss of freshness (nucleotide degradation), growth of Enterobacteriaceae, and fish deterioration (sensory evaluation). Such preservative effect was most remarkable for fish that were subsequently submitted to electrical stunning, as they had the lowest demerit scores and greatest shelf life in the sensory evaluation. Our results showed that preslaughter anesthesia with EO of L. alba followed by electrical stunning can delay the loss of freshness and extend fish shelf life during chilled storage.     

Electrical stunning of farmed Atlantic cod Gadus morhua L.: a comparison of an industrial and experimental method

An industrial and experimental electrical method for stunning farmed Atlantic cod in air and seawater (SW), respectively, were compared. The impacts of sedation with AQUI‐S^? and exercise to exhaustion before electrical stunning were also assessed to monitor the possible depletion of rested muscle energy levels by electrical stunning. Stress (blood glucose, haematocrit, muscle pH, muscle excitability, high‐energy phosphates and rigor mortis) and flesh quality (fillet texture, colour, liquid leakage (LL), gaping, residual blood and K‐value) were assessed. For the industrial stunning method, an average of 41 V, 0.2 A dc was applied to individual cod for 18–27 s. For the SW method, a bipolar square wave current (170 Hz, 33% duty cycle) was applied for 5 s. After stunning, recovery was prevented by exsanguination in chilled SW. There were no differences (P>0.05) between the two stunning methods except for a higher ultimate fillet pH for cod stunned in air 8 days postmortem. Exercise before stunning depleted muscle energy levels at slaughter, increased LL and fillets had redder and darker flesh after storage on ice for 8 days. Electrical stunning (in air) of AQUI‐S^?‐treated fish partly depleted muscle energy levels (pH 7.3, ATP 18.7 μmol g^?1, PCr 70.1 μmol g^?1). However, flesh quality was not affected. Unless pre‐rigor filleting is the chosen processing strategy, electrical stunning of cod seems to be a promising stunning method.     

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.     

Field evaluation of live chilling with CO2 on stunning Atlantic salmon (Salmo salar) and the subsequent effect on quality

Atlantic salmon were slaughtered in three ways on a commercial slaughter line: (1) killed by a percussive stun after crowding; (2) killed by percussive stun after crowding, pumping and live chilling; (3) killed by exsanguination after crowding, pumping and live chilling. The live‐chilled fish were exposed to seawater (2°C) saturated with carbon dioxide (pH 5.5–5.7) for 40 min. The fish were calm after live chilling, but not unconscious, as eye rolling was observed in all individuals. Subsequent exsanguination of the unstunned fish resulted in death. Both rapid live chilling and the subsequent exsanguination appeared stressful to the fish, as a large and rapid pH drop coupled with earlier onset of rigor mortis, indicative of high muscle activity during the process were observed. The muscle core temperature during ice storage showed that live chilling only has an effect on carcass temperature during the first 6 h post mortem. After 6 h, no significant differences in temperature were detected between live‐chilled and traditionally ice‐chilled fish. We conclude that commercial use of live chilling in combination with high levels of CO₂ does not stun Atlantic salmon. Live chilling followed by exsanguination of the unstunned fish appears to be highly stressful and should be avoided.     

Electrical stunning followed by decapitation or chilling of African catfish (Clarias gariepinus): assessment of behavioural and neural parameters and product quality

The objective of this study was to assess neural and behavioural responses in farmed African catfish (Clarias gariepinus) upon electrical stunning in combination with decapitation or chilling. To assess the possibility of scaling up one or both experimental methods, two trials were performed in an experimental setting. The product quality of the collected samples was compared with the currently applied industrial method: live chilling. After electrical stunning in combination with decapitation, the fish showed spikes alternated with theta and delta waves on the EEG, followed by minimal brain activity after 20±10 s. The same traces on the EEGs were observed after electrical stunning in combination with chilling. Here, minimal brain activity occurred after 22±11 s. Within a confidence level of 95%, the percentage of African catfish that was effectively stunned after administration of an electrical current of 1.5 A dm⁻², 300 V (50 Hz a.c.), followed by decapitation or chilling was above 91%. The analysis yield and evolution of liquid loss showed significant (P<0.05) differences among the batches, which could be explained by the stunning method used. The course values of the pH in the different batches were significantly (P<0.05) dependent on the stunning method, sex and location (visceral or skin side). It is concluded that African catfish can be stunned effectively using electrical stunning in a water tank, followed by decapitation or chilling in ice. Dutch commercial processors prefer to combine electrical stunning with chilling in flake ice in a rotating tumbler, as the outer slime layer is then removed, which facilitates further processing.     

Stunning of farmed African catfish (Clarias gariepinus) using a captive needle pistol; assessment of welfare aspects

The objective of this study was to assess whether high‐pressure injection of air into the brain of African catfish (Clarias gariepinus) could render the animal unconscious and insensible immediately and permanently. In the study, 48 African catfish with a live weight of 900–1900 g were restrained and equipped with EEG and ECG electrodes and then stunned. The catfish were stunned mechanically using a captive needle pistol. The pressure to shoot the needle was 8 bar and that to inject the air was 3 bar for 1.5 s. The catfish behaviour was observed during and after stunning. τ and δ waves and spikes, which precede a stoppage in brain activity as measured on the EEG, were used as indices for the measurement of immediate induction of unconsciousness and insensibility In 23 of 42 fish, an iso‐electric line was observed after an average of 13.4 s, while in the remaining fish the τ and δ waves and spikes remained on the EEG during the recording period. In all cases, the ECG showed an irregular heart rate with fibrillation and extra systolae. Moreover, the configuration showed ischaemia. Before the captive needle stunning, free‐swimming fish (n=7) explored the tank for an average of 21±12 s before lying down at the bottom. After stunning, they showed clonic uncoordinated swimming movements. The movements stopped after an average of 38±50 s. In another group (n=7) that was stunned and subsequently placed in ice water, clonic cramps were observed in two out of seven animals. When taking into account the number of animals with a reliable EEG (n=42) and using 95% confidence intervals, it was concluded that at least 93% of the catfish were effectively stunned using a correctly positioned captive needle pistol. Furthermore, it is recommended to immobilize the stunned fish by chilling, as the post‐stun clonic cramps may hinder gutting and filleting.     

Evaluation of electrical stunning of sea bass (Dicentrarchus labrax) in seawater and killing by chilling: welfare aspects, product quality and possibilities for implementation

The objective was to assess neural, behavioural responses and product quality in farmed sea bass (Dicentrarchus labrax) upon electrical stunning in seawater. The electrical sinusoidal 50 Hz or pulse square wave alternating 133 Hz current induced a general epileptiform insult with a current of 3.3±0.2 or 3 A dm^?2, respectively, for 1 s head to tail in seawater. The total duration of the insult was 48±34 and 23±11 s. After stunning, the electro‐cardiogram revealed fibrillation and ceased or showed malfunction. Product quality was assessed in a group electrically stunned, followed by chilling in ice water and the controls were only chilled in ice water. The pH of the fillets was 0.1–0.2 lower (P<0.01) when stunned electrically at days 1, 2, 8 and 10 postmortem, where the colour did not differ. The percentage of sea bass effectively stunned using an electrical sinusoidal or pulse square wave current was above 85% within a confidence level of 95%. A combination of electrical stunning for 10 s, followed by chilling in seawater with ice flakes resulted in the death of all fish. The former method is recommended to be adapted for implementation in practice.     

Comparison of Stunning Methods on the Physicochemical Properties of Frozen Nile Tilapia (Oreochromis niloticus) Fillets

This study compares how CO₂ narcosis and thermal shock affect the physicochemical aspects of Nile tilapia fillets held frozen (?18°C) for up to 6 months. The characteristics of tilapia fillets subjected to CO₂ narcosis were those of higher lightness and whiteness and lower redness. The hardness values of fillets of tilapia subjected to thermal shock were lower than those subjected to CO₂ narcosis. During frozen storage to both treatments, the drip loss, denaturation of myosin, and lipid oxidation increased, while fillet water holding capacity and hardness decreased. The physicochemical properties of frozen fillets of tilapia stunned by CO₂ narcosis were considered more desirable; therefore, the method can be a potential replacement to thermal shock.     

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.     

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.     

Fillet shelf-life of Atlantic halibut Hippoglossus hippoglossus L. fed elevated levels of α-tocopheryl acetate

Fish fillet quality may be influenced by the antioxidant level in preslaughter diet. Thus, the effects of dietary α‐tocopheryl acetate supplementation and feeding time on the flesh quality of farmed Atlantic halibut Hippoglossus hippoglossus L. were investigated. Halibut of mean initial weight of 312 ± 12.3 g were divided into two groups and fed commercial diets, supplemented with different levels of α‐tocopheryl acetate at the dietary inclusion levels of 189 and 613 mg kg^?1 diet. Fish were sampled after 6,9,12 and 24 weeks. Over the experimental period, they reached a final mean weight of 1320 ± 108.4 g. Tissue α‐tocopherol of fillet and liver was significantly affected by the levels of α‐tocopheryl acetate given with the diets (P < 0.001). In storage on ice, fillets of fish fed the diets high in α‐tocopheryl acetate exhibited significantly lower (P < 0.001) levels of lipid oxidation. The colour of fillets in all groups deteriorated slightly, but diet did not affect this process. Halibut fed the supplemented diets for longer periods were better protected against lipid oxidation (P < 0.001) and colour deterioration (P < 0.01) than those fed for shorter periods. However, after 9 days of storage, lipid oxidation levels were still extremely low [< 0.6 µg malondialdehyde (MDA) g^?1 fillet], even in fillets of fish fed the low α‐tocopheryl acetate diet for a short period preslaughter. Different slaughtering methods tested at the end of the trial showed that percussive stunning can delay the onset of rigor mortis by 8–12 h compared with bleeding of the fish. These results suggest that halibut fillets have enhanced shelf‐life stability even at low doses of dietary α‐tocopheryl acetate, and that other factors in the antioxidant defence mechanisms of the species might play a major role in the prevention of lipid oxidation.     

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.     

A feasible method for humane slaughter of eel (Anguilla anguilla L.): electrical stunning in fresh water prior to gutting

It was observed that farmed eels could be rendered unconscious and insensible instantaneously by passing an electrical current through fresh water. The general epileptiform insult on the EEG was characterized by a tonic/clonic and an exhaustion phase. After stunning, the ECG (electro‐cardiogram) revealed fibrillation. The electrical stunning parameters were on average 194 ± 4 V and 0.636 ± 0.040 A/dm² for 1.6 ± 0.4 s. Within a confidence level of 95%%, taking into account the number of animals with a reliable EEG (n = 29), at least 93% of all eels are effectively stunned in fresh water by an average current of 0.636 ± 0.040 A/dm². The behaviour of groups of five eels, which were able to move freely in the water was observed before and after stunning with 50 V and 0.17 A/dm². After 3‐s stunning, two eels were turned upside down. They changed to a normal position after 10 and 13 s respectively. Subsequently, all eels were very active in swimming behaviour and stopped swimming after 75 s. When stunned for a longer duration, all eels were turned upside down and stopped breathing for a limited period of time. In the last experiment the eels were stunned in fresh water (500 μS) with a voltage of 200 V for approximately 1 s, which was followed by 50 V for 5 min. As soon as the stunning started the water was de‐oxygenated by flushing nitrogen to kill the eels by suffocation during the period of unconsciousness and insensitivity. The oxygen saturation decreased from 74 ± 10 to 23 ± 11% at 22 °C. After stunning no brain activity and no responses to pain stimuli were observed on the EEG. The heart rate increased (P < 0.05) after stunning, which was followed by a significant decrease. Only 1 out of 18 eels returned partially from upside down to a normal position 2 h after stunning; however, the eel did not respond to pain stimuli in behaviour. The developed stunning procedure can be recommended for humane slaughter of 50‐kg batches of eels.     

Effects of rested-harvest using the anesthetic AQUI-S™ on channel catfish,Ictalurus punctatus,physiology and fillet quality

Trials were conducted to determine effects of AQUI-S™ sedation during harvest (rested-harvest) on physiological responses and fillet quality of channel catfish, Ictalurus punctatus. Rested-harvest is defined as application of an anesthetic immediately before harvest to reduce fish activity associated with a normal harvest. Doses of 25–35 ppm AQUI-S™ were effective for rested-harvest of catfish (loss of equilibrium in 3 to 10 min and 100% survival following recovery). Time to loss of equilibrium and time to recovery following sedation with 35 ppm AQUI-S™ increased as water temperature decreased from 30 °C to 10 °C. Catfish exposed to 25 ppm AQUI-S™, 35 ppm AQUI-S™, 100 ppm trincaine methanesulfonate, and 8 ppm metomidate had lower blood lactate, cortisol, and glucose and higher blood pH than unsedated fish exposed to a low-water stress. Rested-harvest (RH) catfish had higher muscle and blood pH, lower blood and muscle lactate, and higher muscle ATP levels than catfish exposed to a 45 min low-water stress. Rates of muscle pH decrease, ATP decrease, and lactate increase accelerated as storage temperature decreased from 15 °C to 5 °C in RH fish acclimated to summer temperatures (33 °C), conversely these rates accelerated as storage temperature increased from 5 °C to 15 °C in RH fish acclimated to winter temperatures (7 °C). Based on physiological response (higher muscle pH, lower blood lactate, delayed time to rigor), post-sedation euthanasia by CO₂ was superior to post-sedation euthanasia by AQUI-S™ overdose (150 ppm), nitrogen gas, or electrical stunning. Compared to fillets from fish exposed to simulated industry transport conditions, fillets from RH/CO₂ euthanised fish had higher pH 1 h post-slaughter, and less drip-loss and lower L^⁎ and a^⁎ color values during 7 days of iced storage. RH/CO₂ and control fillets were not different for shelf-life based on bacterial counts. Rested-harvest with AQUI-S™ followed by CO₂ euthanasia has potential to improve catfish fillet quality, but AQUI-S™ approval, development of rested-harvest strategies, and demonstration of economic benefits of rested-harvest will be required for adoption of rested-harvest to commercial catfish production.     

Is humane slaughter of fish possible for industry?

Abstract The objective was to evaluate industrial and research slaughter methods for Atlantic salmon (Salmo salar), gilt‐head seabream (Sparus auratus) and eel (Anguilla anguilla) with respect to welfare and quality. As a general term of reference, an optimal slaughter method should render fish unconscious until death without avoidable excitement, pain or suffering prior to killing. For Atlantic salmon, commercial slaughter methods (carbon dioxide stunning followed by gill cutting, and gill cutting alone) are not in conformity with the general term of reference, as the fish are not rendered unconscious immediately and possibly experience stress. Evaluation of automated percussive stunning remained unconclusive. More research should enable us to ascertain whether loss of consciousness is instantaneous. Electrical stunning can be humane if applied properly. However, because flesh of electrostunned fish was characterized by occasional bloodspots, optimization of the electrical parameters is required. Prototypes for percussive and electrical stunning of salmon have been recently developed. This implies that humane slaughter of salmon is feasible for industry. For gilt‐head seabream, neither aphyxia in air nor transfer of the fish to an ice slurry were considered to be humane: the methods did not induce immediate brain dysfunction and vigorous attempts to escape occurred. Percussive and electrical stunning can be in conformity with the general term of reference. However, conditions for stunning whole batches of seabream have not been established. Quality of the fish slaughtered by percussive stunning was similar to that obtained by the industrial method, i.e. immersion in an ice slurry. Further work is required to establish optimal stunning conditions and to develop prototypes. For eel, desliming in a salt‐bath followed by evisceration, electrical stunning performed under the conditions prescribed by the German legislation, and live chilling and freezing were not considered to be humane. In contrast, it was established that a 10–20 kg batch of eels in fresh water could be rendered unconscious immediately and until death by applying electricity in combination with nitrogen gas. The conditions used were 0.64 A dm^?2 for 1 s, followed by 0.17 A dm^?2 combined with nitrogen flushing for 5 min. A preliminary assessment of flesh quality suggests that it may be improved by application of the latter method, compared with the salt bath. The results clearly indicated that humane slaughter of eels is possible in practice.     

Changes in muscle collagen content during <Emphasis Type="Italic">post mortem</Emphasis> storage of farmed sea bream (<Emphasis Type="Italic">Sparus aurata</Emphasis>): influence on textural properties

The changes in collagen content and its solubility in sea bream muscle were studied for variable storage times following the death of the fish, and these variables were related to the evolution of physical parameters important for consumer acceptance: firmness and water-holding capacity (WHC). The results show that the collagen content in muscle diminished slightly over storage time and that this variable was directly related to firmness but inversely related to the water-holding capacity. With regard to collagen solubility, a decline was detected in acid-soluble collagen (ASC) in the first few post mortem hours, perhaps related to the end of rigor mortis that occurs at these stages. Pepsin-soluble collagen (PSC) increased, while insoluble collagen (ISC) decreased from 96 h, coinciding with a loss of firmness. This softening can be explained as a result of specific collagenases acting on the insoluble fraction of the collagen.     

Evaluation of head-only and head-to-tail electrical stunning of farmed eels (Anguilla anguilla, L.) for the development of a humane slaughter method

The overall objective was to evaluate the suitability of electronarcosis as a stunning method for farmed eels. In the first experiment the minimum electrical current needed to induce a general epileptiform insult by head‐only stunning was assessed. The individual eels (n = 40) with a live weight of 700–800 g were fixed in a specially designed re‐strainer. The EEG (electroencephalogram) and ECG (electrocardiogram) recordings, observation of behaviour and responses to pain stimuli were used to assess unconsciousness, insensibility and cardiac function. The applied current of 150, 200 or 250 V, 50 Hz, AC was delivered via scissor‐model stunning tongs for approximately 1 s. A general epileptiform insult was observed in 31 eels for which a successful EEG recording was obtained, using 255 ± 4 V, 545 ± 32 mA, for 1.2 ± 0.2 s. The general epileptiform insult as measured on the EEG was characterized by a tonic/clonic phase and an exhaustion phase. The behaviour showed one phase: tonic cramps alternated by clonic ones. The heart rate was 22 ± 8 beats min^?1 (n = 23) prior to stunning. After stunning the ECG revealed fibrillation. In the second experiment the behaviour of seven individual eels able to move freely in water was observed after head‐only stunning (250 V). Two phases were distinguished. Limited tonic and clonic cramps combined with backward swimming were followed by heavy clonic cramps combined with unco‐ordinated movements such as jumping out of the water. A distinct exhaustion phase was not observed in all animals. In the third experiment a head‐to‐tail electrical method was examined in 15 eels for rendering the eels unconscious and insensitive prior to slaughter. They were stunned by applying 253 V for 3 s followed by 50 V for 5 min. In the fourth experiment nine eels were head‐only stunned with 260 V for 1 s immediately followed by 50 V for 5 min applied from head to tail. Results obtained in these two experiments were similar. After stunning no brain activity and no responses to pain stimuli on the EEG were observed and the ECG showed ventricular extra systolae. It was observed that it might take 60 ± 25 min or longer for a complete recovery. It can be concluded that for effective electrical stunning of eels with a weight of 700–800 g an average current of 545 ± 32 mA (at approximate 250 V, 50 Hz AC) is needed. In this case, within a confidence level of 95% at least 91% of the eels are effectively stunned (n = 31). Therefore, it is recommended to increase the minimum current for an effective stun in practice to 600 mA. Further research is needed to determine the conditions to induce permanent unconsciousness and insensibility of the eels to protect the animals at slaughter.