Bjorn Roth

Brain activity of Atlantic salmon (Salmo salar) following electrical stunning using various field strengths and pulse durations

The aim of this study was to investigate the effect of alternating current (a.c.) stunning on brain activity in Atlantic salmon (Salmo salar). Electroencephalography (EEG) was used to determine loss and return of consciousness following stunning. Three groups of salmon were stunned in seawater using 50 Hz sinusoidal a.c., with field strengths equal to 200, 50 and 25 V/m at current durations 1, 3 and 12 s. After stunning, visual evoked responses (VERs) were measured by EEG of the optic tectum. Results showed that all electrically stunned fish lost VERs, and that time to recovery of VERs was dependent on the combination of current duration and electric field strength. Hence, high voltage stunning, using 200 V/m in 1 s resulted in a mean recovery time of VERs equal to 154 s, while low voltage stunning at 50–25 V/m in 3 and 12 s, the time to recovery was 288 and 212 s, respectively. These results show that electrical stunning can cause immediate loss of consciousness in fish, and can be applied as a stunning method prior to slaughter. D 2003 Elsevier Science B.V. All rights reserved.

Effect of Electric Field Strength and Current Duration on Stunning and Injuries in Market-Sized Atlantic Salmon Held in Seawater

Abstract We evaluated electricity as a stunning method before slaughter of Atlantic salmon Salmo salar by assessing both stunning effectiveness and injuries. About 300 salmon (1.2–6.6 kg) were exposed to one-phase, sinusoidal, 50-Hz AC in seawater; electrical field strengths ranged from 15 to 250 V/m and current durations from 0.2 to 12 s. We measured the duration of the epileptic-like seizures after stunning and the degree of unconsciousness based on behavioral responses. Fish were killed, bled, and gutted 10 min after stunning and then analyzed for injuries. The proportion of fish sufficiently stunned, the duration of an unconscious condition, and the occurrence of broken vertebrae and hemorrhages were all dependent on electric field strength and current duration. The electric field strength required to stun the fish was inversely proportional to the current duration, dropping from 200 V/m at 0.8 s to 25 V/m at 6–12 s. Electricity proved to be efficient in stunning fish, but to avoid injuries in market-...

Ability of Electric Field Strength, Frequency, and Current Duration to Stun Farmed Atlantic Salmon and Pollock and Relations to Observed Injuries Using Sinusoidal and Square Wave Alternating Current

Abstract The effects of electricity as a stunning method in the slaughtering process of Atlantic salmon Salmo salar and pollock Pollachius virens were studied. About 330 slaughter-sized Atlantic salmon were exposed to sinusoidal alternating current (AC) in seawater. Electrical field strength ranged from 25 to 100 V/m and current duration from 1 to 10 s at frequencies between 30 and 2,000 Hz. In addition, 122 pollock and 25 salmon were stunned by applying square wave AC in the range of 50–1,000 Hz. After stunning, subsequent unconsciousness was evaluated by means of behavioral responses, and injuries were observed by examining fillets. For sinusoidal AC, the proportion of Atlantic salmon sufficiently stunned and the occurrences of obviously broken spinal columns and hemorrhages were dependent on the electrical frequency used. The AC frequency was the most predominant factor in both stunning and inflicted injuries. The proportion of injured salmon exhibited a unimodal response to sinusoidal AC frequency, in...

Plasma insulin-like growth factor-I concentrations and growth in juvenile halibut (Hippoglossus hippoglossus): Effects of photoperiods and feeding regimes

The effects of photoperiod and feeding regimes on plasma IGF-I levels and their relationship with growth rate of juvenile halibut (initial mean weight 364 g) were investigated by rearing fish under five different photoperiod regimes and two feeding regimes for 14 months. The entire photoperiod experiment was divided into 3 phases where the fish in each phase were exposed to either natural photoperiod (N), stimulated photoperiod with long day and short night (S) or continuous light (L). Thus, the following five photoperiod combinations were tested: a) Control group (NNN) b) Group 2A (NLN) c) Group 2B (NNL) d) Long day-natural group (SNN) e) Production group (LNN). In addition, the Control group was split into two parts and fed according to two different feeding regimes: a) Continuous fed group: Fish fed every day. b) Starvation/re-fed group: Fish were starved for 5 weeks and then re-fed for 10 weeks, and the treatment repeated during the whole experimental period. The analyses of IGF-I were performed from individually tagged fish in all groups in September 2005 and March 2006. In order to test how rapidly starvation affects circulating IGF-I levels samples were taken from the Starvation/re-fed group after a 10 days starvation (September) and immediately after 10 weeks of feeding (March). A significant relationship between IGF-I levels and individual growth in the preceding period and photoperiod and starvation treatment was found on both occasions. In conclusion, the present study indicates that plasma IGF-I levels are correlated to growth in Atlantic halibut, and affected by photoperiod treatment or compensatory growth during re-feeding. Correlation between individual growth rate and IGF-I levels was low, but significant, highlighting the complexity of how environmental factors affect the endocrine and physiological regulation of growth in fish.

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.

Relationship between Muscle pH and Flesh Color of Atlantic Halibut

After 7 d of ice storage, the muscle pH and flesh color (CIE L*, a*, b*) was measured in 118 Atlantic halibut (Hippoglossus hippoglossus) slaughtered at different times of the year. All fish originated from the same stock and the fish were farmed under natural and continuous light and slaughtered fed or starved, representing a wide distribution of fish undergoing different stages of growth, maturation, and sizes (1.5 to 5.9 kg). Results show a considerable variation of end pH ranging from 5.7 to 6.8. The color correlated significantly with muscle pH with R = -0.63, 0.61, and -0.57 for L*, a*, and b*, respectively, while fillet weight and sampling position on the fillet had less influence on color. We conclude that the end pH of the muscle is an important factor for the visual quality of fish, and in particular for Atlantic halibut. Therefore, measures should be taken to avoid high glycogen levels at death, as this will have a large impact on the muscle pH, with negative consequences for flesh color.

Slaughter of Atlantic salmon (Salmo salar L.) in the presence of carbon monoxide

The different stunning methods for Atlantic salmon can still be improved with regard to animal welfare. Salmon exposed to carbon monoxide expressed no aversive reactions towards CO as such. CO exposed fish showed an earlier onset of rigour mortis and a faster decrease in muscle pH due to depletion of oxygen during the treatment. Exposure to CO did increase the level of cortisol compared to undisturbed control fish, but the increase was less than in the water only control group. Neuroglobin, a CO binding globin, was found in salmon brain and Saccus vasculosus, a richly vascularized sac connected to the fish brain. Binding of CO to neuroglobin during sedation might possibly improve animal welfare.

The Shelf Life of Farmed Turbot (Scophthalmus maximus)

A total of 18 farmed turbot (Scophthalmus maximus) were slaughtered over 4 successive weeks in November 2012 and stored in polystyrene boxes with ice until analyzed. The fish were stored between 1 and 22 d and presented to a taste panel and further analyzed for quality index method (QIM), microbiological analysis by real-time quantitative PCR (qPCR), taste, pH, color by computer imaging, protein denaturation with differential scanner calorimeter (DSC), texture hardness, and shear force. Results show small, but significant changes in physical and visual attributes such as texture and color. No gaping was observed. Only small changes in texture were observed explained by lack of myosin denaturation. The fillets became more white and yellow during storage, whereas the major changes occurred during the 1st week. A panel evaluating QIM and taste could not distinguish major differences in appearance and taste and over 15 d storage period, but were able to quantify the age by smell. Analysis of microorganisms on the epidermis displayed growth of Carnobacterium maltaromaticum, potentially inhibiting growth of other spoilage bacteria. Fish stored for 22 d were rejected by the taste panel caused by a stale smell and taste, but not bitter or rancid. It is concluded that turbot has a shelf life of at least 16 d.

A comparative study of diploid versus triploid Atlantic salmon (Salmo salar L.). The effects of rearing temperatures (5, 10 and 15 °C) on raw material characteristics and storage quality

Several major market operators argue that the current level of knowledge about quality is too scant to justify a switch to a large-scale production of triploid salmon. The aim of the present study was, therefore, to elucidate how rearing conditions (5, 10 and 15°C) affect the flesh quality of triploid Atlantic salmon (Salmo salar L., 1.6±0.3kg). As a reference, diploid salmon kept under equal conditions and with equal genetics were used. The main design discriminant was the holding temperature; increased temperature gave increased blood lactate, rigor index (Ir), drip loss (DL), content of astaxanthin and intensity of redness, but reduced muscle pH, cathepsin activity and fillet lightness. Salmon kept at 10°C grew the fastest. It is concluded that ploidy gave less variation than temperature. Triploids were characterized by lower blood haematocrit (Hct) and Ir, higher DL and collagenase activity, and on average, paler and less yellowish fillets.

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

UNLABELLED 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. PRACTICAL APPLICATION 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.