Live Chilling Research Articles

Impact of Pre-Slaughter Methods on the Overall Quality of Nile Tilapia (Oreochromis niloticus)

ABSTRACT In Brazil, tilapia represented 57% of the total fish production. This study aimed assess the influence of different pre-slaughter methods (live chilling in ice/water (LC); anesthesia with the essential oils Ocimum americanum (OA) or Lippia alba (LA) and mechanical spiking (SP), on the meat quality parameters of Nile tilapia. The rigor mortis index showed faster onset in the LC group compared to the OA and LA groups after 3 hours. The pH value, TVB-N, and K-value remained unchanged, indicating no detrimental effects on meat quality. Mechanical spiking and essential oil anesthesia had comparable effects to live chilling.

Fish slaughter practices in Brazilian aquaculture and their consequences for animal welfare

AbstractSlaughter is considered an important fish welfare issue. For a slaughter method to be considered humane, effective stunning that lasts until death as well as the reduction of pain and fear throughout all procedures are essential. Our objective was to investigate current techniques for slaughtering fish in Brazil. A digital questionnaire with six multiple-choice and three open questions was distributed to companies registered as fish slaughterhouses and to fish farms in 2019, addressing fish species, quantities processed and slaughter procedures adopted. From 62 facilities in 15 Brazilian states that answered the survey, nine slaughterhouses and 30 fish farms slaughtered fish, totalling 452 tonnes per day. All reported pre-slaughter stunning, and live chilling to be the most commonly cited method (82.0%), followed by electronarcosis (18.0%). Slaughtering techniques included exsanguination (38.5%) and decapitation (2.5%). For the remaining companies, no slaughter method was declared, suggesting death by asphyxiation or by further processing (59.0%). Twenty-nine companies adopted pre-slaughter fasting, lasting from 10 to 48 h. All sites worked with tilapia (100%) and 24 (82.7%) reported that they worked exclusively with this species. Other species reported were: pacu (25.6%), tambacu (17.9%), tambaqui and carp (15.3%), jundiá (12.8%), pintado and pirarucu (7.7%), matrinxã and pangassius (5.1%). Asphyxia and live chilling are not considered humane, as animals remain conscious and, thus, suffer. Results show that most establishments do not perform humane slaughter. This scenario highlights the urgent need for development and enforcement of humane fish slaughter techniques, with routine supervision and normative requirements.

Effect of ice stunning versus electronarcosis on stress response and flesh quality of rainbow trout

In recent years, concerns about fish welfare have increased in aquaculture, most pointedly regarding the slaughter process. Immersion in ice water (live chilling) is still commonly used as a stunning method in salmonids, but can have negative effects on the stress response and flesh quality. A valid alternative is electronarcosis, but the specific details of the intensity and frequency of the current applied depend on the species and size, and little is known about how that may affect fish welfare or product quality. In this study, adult rainbow trout (294 ± 8.44 g average weight) were subjected to three different stunning methods before slaughter: immersion in ice water and electronarcosis at two different current intensities (200 or 400 mA). Electronarcosis caused fish to lose consciousness faster than those live chilled. Plasma concentration of cortisol was lower in fish stunned with 400 mA (400 mA: 5.2 ± 0.67 vs. Ice: 9.1 ± 0.90; 200 mA: 9.3 ± 1.20 ng/ml). Creatine-phosphokinase enzyme levels were higher in ice stunned fish compared to electronarcosis (Ice: 168 ± 2.32 vs. 200 mA: 114 ± 0.89; 400 mA: 104 ± 0.62 U/l). Regarding flesh quality, initial muscle pH was lower in fish stunned by ice immersion than by electronarcosis (Ice: 6.49 ± 0.034 vs. 200 mA: 6.76 ± 0.050; 400 mA: 6.61 ± 0.04), presenting also an earlier onset of rigor mortis. Fish stunned with 400 mA electronarcosis also presented higher levels of muscle glycogen than those stunned with ice water (0.181 ± 0.029 vs. 0.101 ± 0.013 mg/g). In conclusion, electronarcosis is a stunning method that can produce an immediate loss of consciousness in rainbow trout, reducing stress response before slaughter and improving flesh quality (with higher benefits using a current intensity of 400 mA), in contrast to immersion in ice water.

Physiological response of temperature shocks in turbot and sole

ABSTRACTIn the present study, selected temperature drops were examined to investigate the effects of live chilling on stress and welfare in turbot and sole. This study demonstrated that rapid temperature drops from 11°C–12°C and 18°C–18.7°C to 4°C–0°C in turbot resulted in higher blood sodium and potassium at 0°C (164 mmol l−1, 4.4 mmol −1) compared to 4°C (153 mmol l−1, 3.1 mmol −1), indicating osmoregulatory disturbance. A rapid temperature drop from 18°C to 0°C in Senegal sole also resulted in higher blood sodium and potassium at 0°C (164 mmol l−1, 4.8 mmol −1) compared to the control group at 18°C (157 mmol l−1, 3.2 mmol −1). Based on present findings, we conclude that immersion in ice water will have a negative effect on the animal osmoregulatory capacity, and we recommend that turbot and sole are stunned before slaughter.

Pre-mortem stress and the subsequent effect on flesh quality of pre-rigor filleted Atlantic salmon (Salmo salar L.) during ice storage

The impact of pre-mortem stress and the subsequent effect on flesh quality of pre-rigor filleted Atlantic salmon (Salmo salar L.) was investigated. Market-sized salmon were sampled before or during crowding, and before and after pumping and live chilling, representing accumulating stress and fatigue. Blood parameters (pH, Na+, iCa, pCO2, pO2, glucose, Hct, lactate) and muscle pH confirm a stepwise increase of stress, depending on whether the fish were uncrowded (control), just crowded, uncrowded and chilled or crowded and chilled. Drip loss, water-holding capacity (WHC) and muscle pH during ice storage were not affected by pre-slaughtering conditions. However, a significant effect of storage time was observed. Significantly lowest firmness (N) was observed in crowded and chilled salmon whereas the cathepsin L activity was found to be significantly affected by crowding, live chilling and storage time. Moreover, small effects were observed regarding colour and contents of free amino acids.

Effects of different slaughtering methods on rigor mortis development and flesh quality of tench (Tinca tinca )

Summary The effects of different slaughtering methods on rigor mortis and flesh quality parameters were investigated. Eighty tench were divided into four groups, whereby each group was slaughtered using a different method: percussive stunning (PS), live chilling (LC), asphyxia (CO2), or electrical stunning (ES). Progression of rigor mortis (RM) was recorded (30 h) as well as pH, colour, cooking losses, texture, drip losses and free water after 24 h of storage at +2°C. The PS group showed a delayed onset of RM when compared to the other groups and with a later beginning of rigor resolution. The highest rigor index values were shown in the PS and CO2 groups, and were reached at 24 and 20 h post-mortem, respectively. ES fish exhibited a significantly faster rigor onset when compared to the PS group. At 24 h, pH was not affected by the stunning methodology, nor were the colour or texture characteristics, even when a trend was observed (PS>ES>CO2>LC) for the latter parameter. This research is evidence of how stunning procedures prior to slaughter have a significant effect on rigor mortis development, whereas no differences were found concerning quality parameters.

Effects of green tea natural extract on quality parameters and lipid oxidation during storage of tench (Tinca tinca ) fillets

Summary The study investigated the effects of two levels of green tea extract (GTE) on common quality parameters and lipid oxidation of tench fillets for up to 7 days of refrigerated (+2°C) and 45 days of frozen storage (−25°C). Sixty-eight tench (93.2 ± 25.7 g) were killed by live chilling (water : ice ratio = 1 : 1; T = 2–4°C) and then filleted. Four fillets were set aside (not treated, NT) while the remaining were divided into four groups which were treated with a sprayed-on solution of: distilled water/ethanol 95% v/v mixture (control group, C); ascorbic acid (AA); and two levels of GTE (0.05% w/v GTE5 and 0.1% w/v GTE10, respectively). Tested were fillet quality parameters (pH, colour, fillets texture and water holding capacity), chemical composition, and lipid oxidation products. Moreover, in NT and refrigerated fillets the total viable counts, Enterobacteriaceae, Pseudomonas spp., yeast and moulds microorganisms were assessed. Results showed that GTE at both levels had no negative effects on pH, colour, texture or free water, with results comparable to AA used as a reference synthetic antioxidant. At 7 days of refrigeration, the GTE-treated fillets showed a similar antioxidant capacity of synthetic AA in retarding lipid oxidation. In frozen samples, the best results were obtained by GTE5 treatment while GTE10 seemed to exert a pro-oxidant effect. No significant inhibitory effects of GTE were observed in the microbiological parameters.

Effect of Blood Removal Protocol and Superchilling on Quality Parameters of Prerigor Filleted Farmed Atlantic Cod (Gadus morhua)

A total of 40 farmed Atlantic cod (Gadus morhua) were in 2 groups either fillet directly after stunning and spray washed or produced into fillets according to traditional slaughter methods including exsanguination for 30 min, gutting and washing. Both groups were either stored superchilled or traditionally on ice. After 7 d postmortem color (CIE L*, a*, b*) and fillet shrinkage was measured by computer imaging along with drip loss and texture hardness. Results show that superchilled fillets had significant lower core temperature than fillets stored on ice during the entire 7 d storage period. This resulted in reduced fillet shrinkage from 14.7% to 6.9% and less drip loss dropping from 9.45% to 3.99% in average. Processing the fish directly into fillets resulted in satisfactory blood drainage, where all groups were in particularly well exsanguinated with a* values below zero. No color difference was observed between filleting groups or chilling methods. Spray washing of the fillets resulted in water uptake and higher drip loss in interaction with chilling method. We conclude that filleting farmed fish in one step is feasible. Traditionally farmed fish are slaughtered and processed over several steps, which often include live chilling, stunning, exsanguination, chilling, gutting, rinsing, decapitation, filleting before the fillets are packed into polystyrene boxes and shipped with ice. These processes are often time, laboring, space, and energy consuming. A novel processing line for filleting of farmed fish is gutting and filleting the fish directly after decapitation and replacing exsanguination with spray washing the fillets. In addition, all the cooling steps are replaced by superchilling the fillets. This novel process line gives fillets with comparable if not superior quality compared to the traditional process.

Impact of Handling and Pre-Mortal Stress on the Flesh Quality of Common Carp (Cyprinus carpio L.)

The aim of this study was to investigate stress in common carp Cyprinus carpio L. caused by harvesting, transport, and the stunning method, and the effect of the latter on flesh quality Serum cortisol concentration increased during harvesting and transport. The percussive stunning (blow on head) method caused the least stress and resulted in a significant increase in blood cortisol concentration (P<0.01). This method had no significant effect on conventional flesh quality. CO2 asphyxiation which was more stressful delayed stiffening in rigor mortis development. The greatest stress was caused by live chilling. There was a decline of pH levels in the CO2 asphyxiated and live chilled groups compared to the percussive stunned group. According to our results percussive stunning led to the best fillet quality and is the least objectionable method according to animal welfare standards.

Live chilling of Atlantic salmon: physiological response to handling and temperature decrease on welfare

Investigation of the physiological effects of live chilling in Atlantic salmon, Salmo salar, has been performed in two experiments. In the first, fish (mean weight 840 g) acclimatized to either 16, 8, or 4°C were directly transferred horizontally or vertically (9 combinations) to water temperatures of 16, 8, 4, or 0°C using a dip net. Blood samples were collected at 1 and 6 h (h) post-transfer. In the second experiment, fish (mean weight 916 g) acclimatized to 16°C were exposed to four temperature-drop regimes (no physical handling): 16-4°C (over 5 h), 16-4°C (over 1 h), 16-0°C (over 5 h), and 16-0°C (over 1 h). Blood samples were collected 1 h post-temperature drop. Physical transfers in the first trial, i.e., temperature drops, resulted in immediate (1 h) increases in blood lactate concentrations at all three temperatures, but levels were significantly reduced and close to pre-transfer levels after 6 h. Horizontal transfers, i.e., 16-16°C, 8-8°C, and 4-4°C, resulted in similar increases and were not significantly different from the groups exposed to temperature drops. The most severe vertical transfer (16-0) resulted in a swift loss of equilibrium and eventually death. In experiment 2, temperature drops from 16 to 4°C and from 16 to 0°C over a period of one or 5 h, without physically handling the fish, resulted in no significant increases in any of the measured parameters 1 h post-transfer, except in the 16-0 (1 h) group. The latter experienced a significant increase in blood sodium, glucose, lactate, and cortisol levels compared to all other groups. The results suggest that salmon are capable of tolerating relatively steep temperature drops without any significant negative effects on blood stress parameters and that physical stress from handling overrides the effect of thermal insults.

Species‐specific welfare aspects of the main systems of stunning and killing of farmed Carp

Species‐specific welfare aspects of the main systems of stunning and killing of farmed Carp

Live chilling of turbot and subsequent effect on behaviour, muscle stiffness, muscle quality, blood gases and chemistry

AbstractDuring the commercial slaughter of farmed turbot(Scophthalmus maximus), a total of 67 fish were, on six occasions, removed from their rearing conditions at 14°C and put, as is standard commercial practice, into chilled seawater (-1.5 to -0.8°C) to monitor behavioural, muscular, osmoregulatory and respiratory responses during chilling time (90 min). Results show that a thermal insult alters the iso-osmotic balance, leading not only to an Na+influx and an intracellular release of Ca2+and K+, but also to a disturbance of respiratory function, leading to acidosis as a result of H+ and CO2accumulation, increased pCO2and reduced HCO3−in the blood. Once the internal temperature dropped below 1°C, the muscles contracted (cold shortening) and, although the fish were still alive, they reverted to a state of rigor, leading to a complete breakdown in their ability to move or ventilate and resembling an unconscious condition or death. Remarkably, the fish were able to prevent themselves undergoing hypoxia as pO2remained within acceptable limits. No changes in muscle pH were observed and, thus, no noted effects on textural properties. We conclude that live chilling from 14°C to approximately -1°C is a highly questionable practice. It causes physical and physiological changes that are generally associated with stress and, in the case of observed forced muscle contractions, could lead to severe pain. Furthermore, we conclude that cold shortening associated with chilling can be easily mistaken forrigor mortisand, as such, should be subject to further attention in future research on quality.

Stunning, pre slaughter and filleting conditions of Atlantic salmon and subsequent effect on flesh quality on fresh and smoked fillets

The aim of this study was to investigate how stunning methods in combination with pre slaughter conditions such as pumping and live chilling influence the flesh quality in both fresh and smoked products of Atlantic salmon ( Salmo salar). For quality measurements, a total of 181 fish were percussive stunned at the 1) cage, 2) after pumping and 3) after live chilling, where half of the fish were stimulated with 16 s of electricity in order to simulate electrical stunning. Muscle pH and rigor index were measured for 4 days in 10 fish from each group ( n = 60). The other 121 fish were either pre ( n = 57) or post rigor filleted ( n = 64). After 7 days on ice storage one fillets from each fish was analyzed for gaping, color, drip loss, and texture hardness, while the other fillet was dry salted and smoked and evaluated 14 days post mortem. Muscle pH and time to onset of rigor decreased according to the number of events (pumping, live chilling and electrical stunning). For fresh fillets the filleting method was the predominant factor for the end quality overshadowing the influence of pre slaughter conditions and stunning method. Salting and smoking eliminated differences caused by slaughter or filleting methods. We conclude that the quality of Atlantic salmon is influenced in following order: stunning method < pre slaughter conditions < filleting method < processing by salting and smoking.

Live Chilling and Carbon Dioxide Sedation at Slaughter of Farmed Atlantic Salmon: A Description of a Number of Commercial Case Studies

ABSTRACT Eleven commercial processing lines for the slaughter of Atlantic salmon were evaluated to investigate the efficiency of the refrigerated seawater live chilling method with respect to stunning fish and reducing body temperature. The method is commonly used in the Norwegian salmon industry to both stun and chill fish before killing. Carbon dioxide gas was added to the live chilling tanks, or in some cases, to a subsequent carbon dioxide stunning tank. Criteria used for evaluation were water quality parameters (dissolved oxygen, carbon dioxide, pH, temperature, total ammonium, ammonia, alkalinity, color, total organic carbon, and ferric ion), fish behavior, white muscle pH, and body and core temperatures. At two processing plants, fillet quality (Roche color, texture, ultimate pH, and water content) was also determined. The results are discussed in terms of fish acclimation temperatures, water quality, welfare, handling stress, chilling efficiency, pre-live chilling factors, refrigerated seawater live chilling process parameters, and fillet quality. Even though the live chilling method can be used to minimize fish handling stress during slaughter and may serve as an efficient chilling method, it was found in most cases that under commercial conditions when large biomasses were slaughtered, both handling stress and chilling efficiency were less than optimal. However, no adverse effects on the fillet texture and color were observed as a result of fish processing.

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.

Assessment of electrical stunning in fresh water of African Catfish ( Clarias gariepinus) and chilling in ice water for loss of consciousness and sensibility

The overall objective of the study was to evaluate loss of consciousness and sensibility after electrical stunning in fresh water and live chilling in ice water for slaughter of African catfish using measurement of electrical brain and heart activity. To provoke immediate loss of consciousness and insensibility, the minimum electrical current needed to induce a general epileptiform insult was assessed by placing a fish one by one in a tank between 2 plate electrodes in fresh water. The general epileptiform insult on the EEG (electroencephalogram) was characterised by a tonic, clonic and an exhaustion phase. After stunning, the ECG (electrocardiogram) revealed fibrillation. Within a confidence level of 95%, taking into account the number of animals with a reliable EEG ( n = 24), at least 88% of all catfish are effectively stunned in fresh water by an average current of 1.60 ± 0.11 A/dm 2 (50 Hz, sinusoidal, a.c.) at a conductivity of 876 μS of the water. After electrical stunning in combination with decapitation the fishes showed minimal brain activity until death by bleeding. For assessment of live chilling, 28 individual catfish kept in aerated tap water of 24 °C were placed one by one in ice water of 0.1 ± 0.5 °C for 30 min. The fishes showed swimming followed by clonic muscle cramps and became motionless at the end. No response on pain stimuli on the EEG appeared after a median of 12.5 min (5 to 20 min) at a body temperature of 13.7 ± 2.6 °C ( n = 22). When taking into account the number of animals with a reliable EEG ( n = 22) and using 95% confidence intervals, it was concluded that at least 87% of the catfish were unconscious and insensible at a decrease in body temperature of approximately 8.7 °C. Live chilling of African catfish resulted in an extremely high heart rate (tachycardia). Values between 294 ± 47 and 311 ± 38 beats/min ( n = 13) were measured, where a normal value is between 70 and 80 beats/min. It was observed that unconscious and insensibility can be induced instantaneously by electrical stunning in fresh water. To kill the fish for slaughter decapitation is an option. Live chilling appeared to be a slow method. Whilst the African catfish was still conscious and sensible muscle cramps and tachycardia both occurred which may indicate stress.

Live chilling of Atlantic salmon ( Salmo salar) combined with mild carbon dioxide anaesthesia : I. Establishing a method for large-scale processing of farmed fish

The goal of the present study is to evaluate the combined effect of live chilling and carbon dioxide narcosis as a potential stunning/chilling method for Atlantic salmon in a commercial slaughter line. Water quality parameters in cage and RSW tanks, handling stress (white muscle pH), body temperature profile as affected by processing, rigor mortis development, and fillet quality (protein and textural properties, fillet pH and colour) after ice storage for 1 and 2 weeks, were evaluated. Fish from sea cage, live chilling RSW tank and carbon dioxide stunning RSW tank were compared. Effects of pumping and live chilling on blood vessels in gill arches were also evaluated. Under the prevailing slaughter conditions, it was shown that by using live chilling with a Δ T (SW vs. RSW) of 8–10 °C, oxygen levels (60–156% saturation) and moderate carbon dioxide levels (37–80 mg l − 1 ), it was possible to process Atlantic salmon without inflicting excessive handling stress. Consequently, the fish exhibited a long pre-rigor period (about 24 h) giving ample time for pre-rigor processing. Moreover, no detrimental effects on blood vessels in gills and fillet quality were observed, i.e. the processed fish were not different from the fish taken directly from sea cage. The proposed stunning method of combining live chilling and moderate levels of carbon dioxide in a single tank was considered to be superior to the traditional carbon dioxide stunning method using very high levels of carbon dioxide in a comparatively small tank.

Head-only electrical stunning and bleeding of African catfish(Clarias gariepinus): assessment of loss of consciousness

AbstractThe objective was to evaluate the welfare implications of electrical stunning prior to gill-cutting of farmed African catfish as an alternative to live chilling in combination with gutting. Electroencephalogram (EEG) and electrocardiogram (ECG) recordings, in combination with observation of behaviour and responses to noxious stimuli, were used to assess brain and cardiac function in African catfish (body-weight 1571 ± 362 g [mean ± standard deviation], 32 males and 26 females). In the first experiment, the minimum electrical current required to induce a general epileptiform insult by head-only stunning was determined. The individual catfish were fixed in a specially designed restrainer, and applied voltages of 150 V, 200 V, 250 V, 300 V or 350 V (50 Hz AC) were delivered via scissor-model stunning tongs for approximately I s. A general epileptiform insult was observed in 31 fish, for which a successful EEG recording was obtained using 362 ± 32 V, 629 ± 180 mA for 1.2 s. The durations of the tonic, the clonic and the exhaustion phases were 8 ± 3 s, 12 ± 7 s and 7 ± 5 s as measured by EEG, respectively; a distinct exhaustion phase was not clear in II fish. The total duration of the insult was 23 ± 8 s. After the insult the fish recovered. The heart rate was 63 ± 29 beats minIprior to stunning. After stunning, the ECG revealed extrasystole and was irregular. By using an average current of 629 ± 180 mA (at approximately 360 V, 50 Hz AC), at least 91% of fish are effectively stunned with a confidence level of 95%. In the second experiment, the behaviour of 10 individual catfish, which were able to move freely in water, was observed following head-only stunning (370 V). The durations of the tonic, clonic and exhaustion phases in free-swimming fish were II ± 8 s, 20 ± 5 s and 23 ± 20 s, respectively. All fish recovered. In the third experiment, a group of seven catfish was head-only stunned followed by gill-cutting to kill them as a second procedure (ie after recovery from head-only stunning). No brain activity was seen on the EEG 12 ± 5 s after stunning. However, two fish showed responses to noxious stimuli after 2 min and 5 min. A second group of seven catfish was gill-cut only. They responded to noxious stimuli for at least 15 min. The blood loss was 1.2% and I.0% of live weight for the first and second group, respectively. It may be concluded from our results that African catfish are effectively stunned for 23 ± 8 s with a current of 629 ± 180 mA for 1.2 s, after which they recover. Since evoked responses may remain for at least 5 min after stunning and gill-cutting, we recommended that the stunning and killing procedure should be optimised.

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.