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.     

Preslaughter electrical stunning of eels

The current procedures for slaughtering European eels (Anguilla anguilla) for food are very slow and cause suffering. Although there is little legislation for protecting the welfare of fish at slaughter, the legislation covering farmed mammals and birds at slaughter is well defined, requiring that these animals be rendered insensible immediately or without fear or pain prior to being killed. For many mammals and birds this can be achieved using an electrical stun, which is then followed by a procedure that actually kills them, such as exsanguination. This paper reports the investigation of the possibility of using electricity to stun eels, rendering them insensible to pain. Using 1 s duration alternating currents at 50 Hz applied directly across the head of the fish, it was shown that it was possible to stun the fish with currents of 0.1 A and above. Increasing the applied current increased the length of the period of the stun. When the duration of the application of the current was increased to 30 s it was found that the fish could be killed using currents between 0.50 A and 0.95 A. These results show that it is possible to use electricity to instantly stun eels and also to kill them by using longer duration currents. The use of preslaughter electrical stunning at slaughter could allow the welfare of these fish at slaughter to be improved greatly.     

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.     

Effect of electrical stunning at slaughter on the quality of farmed turbot (Psetta maxima)

Food quality aspects of farmed turbot (Psetta maxima) were compared following two methods of slaughter: the current commercial method, by immersion in an ice slurry, which is then dewatered after approximately 20 min, or by first humanely, electrically stunning the fish using a prototype commercial stunner, before immersion in an ice slurry, which is dewatered after 20 min. Quality was assessed for up to 10 days of storage on ice following slaughter. No differences were found between the slaughter methods in terms of an overall carcass quality: overall appearance, haemorrhage, damage, burst gall bladder, staining of the body cavity by leakage from the gut or damage to the spine. No detectable difference was found between the treatments using the industry standard freshness scoring system, the Quality Index Method. Both groups of fish were classified as ‘Fresh’ after 10 days of storage on ice. Using objective measurements of colour, no differences between fish from either treatment were found in fillet colour. Changes in flesh pH were similar in electrically stunned and traditionally killed fish with a mean pH (±SE) at 2 h post‐mortem of 6.80±0.027 declining to 6.44±0.032 at 24 h post‐mortem. Humane electrical stunning of turbot at slaughter neither detectably improved nor decreased product quality as measured between 1 and 10 days of storage on ice.     

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.     

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.     

Seasonal variation in flesh quality, comparison between large and small Atlantic salmon (Salmo salar) transferred into seawater as 0+ or 1+ smolts

The aim of this study was to identify the effect of growth, size and season on the flesh quality of Atlantic salmon (Salmo salar). Following smoltification, two groups of size sorted 0+ and 1+ smolts (four treatment groups in all) were measured for body weight and length in January, June and October 2002. The fish were stored on ice for 4 days before filleted and samples taken for flesh colour, fat/dry content, end pH, gaping score and texture shear force. Large fish upon smoltification grew faster during the first year at sea, while smaller fish grew faster during the second year at sea, resulting in similar weight at slaughter. Season showed the main influence on quality, where fish slaughtered in October had harder texture, higher fat content and redder colour compared to previous samples (P < 0.05). There were only minor differences between the fish slaughtered in January and June (P > 0.15). No significant differences (P > 0.05) were detected as an effect of size or smoltification age when effects of season were accounted for in the statistical model. We conclude that the observed variation in quality was an effect of changes in growth with season. We recommend that actions aimed to halter growth prior to slaughter could be an effective control measure to reduce seasonal quality variations.     

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.     

Response of downstream migrating adult European eels (Anguilla anguilla) to bar racks under experimental conditions

Russon IJ, Kemp PS, Calles O. Response of downstream migrating adult European eels (Anguilla anguilla) to bar racks under experimental conditions.
Ecology of Freshwater Fish 2010: 19: 197–205. © 2010 John Wiley & Sons A/S Abstract – The behavioural response of downstream migrating nonsalmonid fish to hydraulic conditions associated with river infrastructure is poorly understood. The response of downstream migrating adult European eels (Anguilla anguilla) to bar racks (12 mm bar spacing) angled on the vertical and horizontal planes under different flow regimes and during periods of darkness was assessed. Eels predominantly moved along the channel floor and wall, tending to follow routes where turbulence intensity was high. Time taken to approach the racks was greater than expected if fish had moved passively with the flow. Eels did not exhibit clear avoidance behaviour prior to encountering the racks, instead marked changes in behaviour occurred only after physical contact was made with the structure. No impingement or passage through the racks occurred, and passes per approach were high (98.3%), when vertical racks were angled 15°, 30° or 45° relative to the flow. Impingement and passage through the racks only occurred when horizontally inclined racks were placed perpendicular to the flow. The time eels were impinged on the racks was negatively related to discharge when angled at 30° relative to the channel floor, and positively related when upright. Frequency of impingement was higher under low discharge (132.9 ± 16.6 l·s^?1). Impinged eels escaped from racks at approach velocities of 0.90 ± 0.05 m·s^?1. Passage through the upright rack was common under high discharge (278.9 ± 36.2 l·s^?1). The information presented will improve current fish passage criteria for European eels that are required to develop more effective fish passage facilities.     

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.     

Effects of short‐term starvation periods on flesh quality in Arctic charr (Salvelinus alpinus) in different seasons

Possible effects of short‐term starvation on flesh quality in Arctic charr were studied in spring (March) and summer (August). Groups of juvenile Arctic charr (mean weight March 536 g ± 24; August 461 g ± 15 SEM) were starved for 1, 2 and 4 weeks (March) and 1, 2 and 3 (August). After each starvation period, the fish were slaughtered, and flesh samples collected in order to investigate quality and textural properties in the different experimental groups. Starvation had a positive effect on flesh quality giving firmer texture and lower gaping scores. Starved fish had lower cathepsin activity at slaughter, and a similar difference was seen one‐week post mortem. The results showed that the effect of starvation period was seasonally dependent. Starvation had a larger effect in summer, where a three‐week starvation resulted in firmer texture, whereas this was not seen during spring.     

Effect of triploidy on quality traits of shi drum (Umbrina cirrosa L.) until the second rearing year

Carcass and flesh morphometric, reological and chemical traits of triploid (3n) and diploid (2n) shi drum (Umbrina cirrosa L.) were evaluated through 7 months. Three age groups, 17‐, 21‐ and 24‐month‐old fish, were investigated. The effects of ploidy were statistically evaluated and the weight of fish was included in the model as a covariate because triploids grew less than diploids. As expected, fish weight was found to be significantly correlated with all the investigated morphometric traits, but showed a negative correlation with some chemical (pH) and colour traits (lightness) of raw fillet. In comparison with controls, triploid shi drums were characterized by different morphological traits that involved a slender body shape. In triploids, a reduction in condition factor, backbone weight, dressing index and an increase in the agility index were also recorded. When the commercial size (i.e. over 300 g) was achieved, triploids exhibited larger coelomatic and fillet (dorsal white muscle) fat deposition than diploids. Among reological traits, colour and texture were affected by ploidy; raw fillet lightness and cooked flesh tenderness were higher among triploids in all the investigated age groups. As fish were fed with a restricted feeding regimen, fillet fat deposition was supposed to be limited. Thus, the effects of ploidy on reological traits may be only partially explained by lipid fillet amount and are supposed to be more related to different fibre muscle architecture.     

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.     

Texture and Quality Assessment of Ready-to-eat Farmed Obscure Puffer Fish (Takifugu obscurus) Fillet by Evaluating Bacterial and Myofibrillar Degradation and Biochemical Changes during Refrigerated Storage

ABSTRACT

Obscure puffer fish (Takifugu obscurus) flesh, often eaten as raw fish fillet, is susceptible to softening. To investigate the mechanisms for the softening of flesh and changes in firmness, the proliferation of total microbial flora, Enterobacteriaceae, Pseudomonas spp., and lactic acid bacteria (LAB), total volatile basic nitrogen (TVBN), trimethylamine (TMA), and pH were periodically assayed during storage at 0, 4, and 8ºC. Myofibril extraction and separation of puffer fish flesh was carried out and the length of the separated myofibrils was measured periodically using an optical microscope during the entire storage time. Transmission electron microscopy was also used to inspect the changes in myofibrillar characteristics of the fish flesh at the beginning and end of the storage period. The results indicated that lower chilled temperature can contribute to reduced proliferation of microbial flora and less variation in TVBN, TMA, and pH and further maintain the integrity of myofibrils and retain firmness of puffer fish flesh during storage.     

Effects of starvation,subsequent feeding and photoperiod on flesh quality in farmed cod (Gadus morhua)

The study was designed to investigate the effect of four cycles of 5 weeks starvation followed by 10‐week refeeding compared with daily feeding under either natural photoperiod or continuous light (LL) regime on body composition and flesh quality in Atlantic cod in sea cages, northern Norway. The fish were sampled for body composition and flesh quality parameters at the start of the trial, twice at the end of a 10‐week feeding period and twice at the end of a 5‐week starvation period. There was effect of both feeding and light regime on growth, the two starving groups losing weight during starvation and regaining weight during refeeding, and the group under LL being heavier. But, the mean overall growth did not vary between groups. Starvation/refeeding regime resulted in higher slaughter yield, but no overall effect was seen on hepatosomatic index, water content, water holding capacity (WHC), muscle pH, hardness or flesh colour compared with control groups. Continuous light increased gutted weight and slaughter yield, lowered WHC and depressed maturation compared with fish under natural light regime. Increased growth rate resulted in softer fillets and lower muscle pH.     

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.     

The development of stocked eels (Anguilla anguilla) in previously eel‐free Austrian Alpine lakes

Over a period of 34 years (1954–1987), a total of 11.9 million glass eels were stocked all over Austria to improve the yields of commercial fishermen and to make the lakes more attractive for anglers. Nearly half (48%) of the imported glass eels were introduced into natural, previously eel‐free Alpine lakes until stocking ceased in 1988. Twenty‐five years later, their occurrence could be verified in 56% (N = 22) of the Austrian Alpine lakes larger than 50 ha and mean body length had increased to 66 cm. Eels from seven selected Austrian Alpine lakes exhibited a yearly mean increase in length between 0.6 and 1.5 cm, indicating a comparatively poor growth compared with the majority of eel populations from within their natural distribution range. At the same time, high expectations in developing a flourishing eel fishery were not met. In all but one lake, the harvest remained below 3% of the total yearly catch and salmonids remained the dominant target species. During peak harvest in the 1980s, it exceeded 8% in mesotrophic Wallersee (2600 kg). Simulations of stock development indicated that the yield could have been improved, but contrary to earlier expectations eels never became important for local cuisine and catches remained too low for the development of a profitable export business. On the other hand, eels may have contributed to the loss of small‐bodied fish taxa.     

Effects of temperature on vitellogenesis in Japanese eel Anguilla japonica

ABSTRACT:   Cultured immature female Japanese eels acclimated to sea water at either 10 or 20°C were treated weekly with salmon gonadotropin fraction (sGTH) in order to investigate the effects of water temperature on artificial induction of ovarian maturation. In eels maintained at 20°C, ovulation was induced in 11 of 18 fish during the experimental period of 13 weeks, whereas at 10°C all fish showed a low gonadosomatic index (GSI) at the end of the experiment. Plasma vitellogenin levels were higher in eels kept at 20°C than in eels at 10°C throughout the experiment. However, no significant differences were observed in the plasma testosterone and estradiol-17β levels between groups. Eels pretreated with sGTHs at 10°C for 13 weeks were separated to two different temperature (10 and 20°C) groups, and received the same weekly sGTH injections. In eels transferred to 20°C, plasma vitellogenin levels, GSI and oocyte diameter were increased, but these values were maintained at low levels in eels that remained at 10°C. These results clearly indicate that water temperature is an important factor regulating vitellogenesis in the Japanese eel.     

Flesh quality of tilapia Oreochromis niloticus fed solely on raw Spirulina

ABSTRACT:   In order to simplify the food chain in a closed ecological recirculating aquaculture system, raw Spirulina platensis cultivated in 50-L photobioreactors were fed to tilapia Oreochromis niloticus as a uni-feed from the onset of exogenous feeding. The feasibility of using tilapia grown on raw Spirulina (body weight: 155.4 ± 3.9 g, standard length: 16.2 ± 0.2 cm; n  = 3) was investigated for 30 weeks for sashimi (sliced raw meat). Some of the rheological properties of the flesh were measured to clarify the obtained results of sensory evaluations of texture and fatness. The elastic modulus of flesh of the Spirulina -fed fish was significantly higher than that of the control fish (body weight: 168.9 ± 5.8 g, standard length: 17.8 ± 0.5 cm; n  = 3) that were fed commercial diets. In addition, the viscosity of the flesh of the Spirulina -fed fish was significantly lower than that of the control fish. There was no significant difference in the rupture strength between the two treatments. The rheological parameters in the muscle were found to coincide with the results of the sensory assessment. These results suggest that tilapia fed solely on raw Spirulina have a high flesh quality that is suitable for sashimi. The muscle lipid of the raw Spirulina -fed fish had lower levels of non-polar lipids such as triglycerides and partial glycerides, but higher levels of polar lipids such as phosphatidylcholine and phosphatidylethanolamine. The fatty acid profile of the raw Spirulina -fed fish muscle, especially in the polar lipid fraction, was characterized by an abundance of Σn-6 highly unsaturated fatty acids (20:3n-6, 20:4n-6, 22:4n-6, 22:5n-6).