Physiological response and survival of Atlantic mackerel exposed to simulated purse seine crowding and release

Understanding how animals physiologically respond to capture and release from wild capture fishing is fundamental for developing practices that enhance their welfare and survival. As part of purse seine fishing for small pelagic fish in northern European waters, excess and/or unwanted catches are routinely released from the net in a process called slipping. Due to excessive crowding in the net prior to release, post-slipping mortality rates can be unacceptably high. Atlantic mackerel (Scomber scombrus) support large and economically important purse seine fisheries but are known to be particularly vulnerable to such crowding-induced mortality. Developing management advice to promote post-slipping survival for this species is currently challenging, due to a lack of understanding of how crowding influences their physiology. Here we examine the physiological response, recovery and survival of wild caught mackerel exposed to various degrees and durations of simulated crowding stress in a series of sea cage trials. The magnitude of the physiological response and its time to recovery was positively correlated with crowding density and duration and was characterized by cortisol elevation, energy mobilization and anaerobic metabolite accumulation. There were also indications of osmoregulatory disturbance. Skin injury and mortality rates showed a similar positive relationship to crowding density. The physiological disturbance was recoverable for most fish. Instead, the rate at which mortalities developed and the physiological profile of moribund fish indicated that skin injury, likely arising from abrasive contact with netting and other fish during crowding, was the probable cause of mortality. Injured fish also exhibited a loss of allometric condition relative to non-injured survivors. Crowding treatments were potentially confounded by differences in ambient oxygen reduction, water temperature and pre-treatment fish condition between trials, and densities were replicated only once. These results contribute to the development of welfare conscious fishing practices that aim to reduce post-slipping mortality.publishedVersio

Avlusing av laksefisk med Optilice: Effekt på avlusing og fiskevelferd

Optilice er et konsept hvor laksefisk (Salmo salar og Oncorhynchus mykiss) avluses ved bruk av oppvarmet sjøvann. Prinsippet består av 2 skovlhjul som drar fisk gjennom et vannbad, slik at hver fisk får lik behandling både med hensyn til temperatur og eksponeringstid. Systemet har en kapasitet på 100 tonn/t, men kommersielle tester viser at hver linje har god overkapasitet til å mate inn opptil 150 tonn/t i korte perioder. Undersøkelser viser at metoden har en avlusningseffekt på 98-100 % på bevegelige lakselus (Lepeophtheirus salmonis) dersom en nytter rett temperatur for 20-30 s, men liten effekt på fastsittende lus. Metoden kan også nyttes mot bevegelige skottelus (Caligus elongatus). Temperatur synes å ha best effekt fremfor tid og vil variere i henhold til sesong fra 28 °C om våren til 34 °C på sensommeren. Vannet opprettholder tilfredsstillende vannkvalitet gjennom produksjonsprosessen. Blodprøver gir ingen fysiologiske indikasjoner på hypoksi og histologi av gjeller avdekker ingen skader som følge av behandling. Utfordringen er imidlertid fysiske skader som følge av håndtering, både gjennom pumpe, avsiling inn og ut av Optilice. Under gode betingelser vil systemet kunne effektivt avluse fisken, med såpass lite påvirkning at dødeligheten kan understige 0,5 % over en 30 dagers periode, både for laks og ørret. Imidlertid er dette også betinget fiskens evne til å respondere og skade seg selv, noe som er avhengig av art og størrelse. Til tross for lave skade- og dødelighetstall gjennom flere kommersielle kjøringer utgjør fysiske skader gjennom rift, slag, kapp og gjelleblødning fortsatt en god andel av død fisk. Utfra de tall som nå foreligger og tekniske feil som er utbedret kan Optilice ansees som en hurtig og effektiv måte å avluse fisk, samtidig som den ivaretar fiskevelferd. Fiskens velferd er i all hovedsak avhengig av premissene på merdkanten, samt de tekniske betingelser ombord i fartøyet. Vesentlig blir opplæring, standardisere protokoller for bruk og videreutvikling av systemet.Avlusing av laksefisk med Optilice: Effekt på avlusing og fiskevelferdpublishedVersionpublishedVersionpublishedVersio

Assessing the effectiveness of an electrical stunning and chilling protocol for the slaughter of Atlantic mackerel (Scomber scombrus)

Inducing unconsciousness in fish using electrical stunning prior to slaughter may improve fish welfare and fillet quality if such practises can be disseminated into wild capture fisheries. The objectives of this study were to: 1) evaluate if an established slaughter protocol consisting of dry electrical stunning (using a coupled AC/DC current at ≈ 110 Vrms) followed by chilling could be used to stun the wild captured species Atlantic mackerel (Scomber scombrus) unconscious within 0.5 s; 2) determine if death could be induced without consciousness recovery by longer duration stunning (5 s) combined with chilling in an ice/water slurry for 6 min; and 3) examine the extent of quality defects arising from the applied slaughter protocol. We determined consciousness by examination of behavioural responses in a standardised vitality assessment. Out of a sample of 10 mackerel, 9 were assumed to be rendered unconscious by the 0.5 s stun, as determined by the presence of tonic and/or clonic muscle cramping consistent with a general epileptic insult. Assumed unconsciousness was maintained throughout chilling treatment in all fish (n = 25) following a full stun of 5 s. All fish were assumed to have died as a result of the protocol. There was no evidence of spinal damage or haematoma quality defects post filleting. These results suggest that the examined protocol is effective at slaughtering mackerel in a manner consistent with good welfare and without inducing quality defects, but further research is required to verify the unconscious condition via electroencephalogram (EEG) and before the procedure can be applied in wild capture fisheries.publishedVersio

Electrical stunning and killing of Atlantic salmon

Atlantic salmon (Salmo salar) at various size 226-1938 g were placed in electric dry stunning either tailor head- first and then exposed to 50 Hz, 240 V AC for 0.5 and thereafter 9.5 s of electricity. This to verify whether the animal is rendered unconscious prior to killing by immersing the animal into cold brine (-14 to -18 °C) or hypoxic water, supersaturated with CO2. In addition, salmon from 2000 to 5000 g were exposed to head stunning only. Behaviour, heart (ECG) and brain (EEG) activity were monitored until animal was classed as dead. Post the treatment, the internal temperature of the animal was measured placing loggers into the neuro and heart cavity. The electric potential across the brain was also measured. A preliminary evaluation of the EEG and ECG registrations in the individual fish showed that loss of consciousness can be induced within 0.5 second and consciousness can be prolonged without recovery when the cold brine or seawater saturated with carbon dioxide is applied as killing method. Our results also suggest that the current can be applied head to tail, which facilitates immediate stunning of Atlantic salmon in a commercial setting. We conclude that electrical stunning in combination with cold brine is effective for humane stunning and killing Atlantic salmon.Electrical stunning and killing of Atlantic salmonpublishedVersio

Physiological and flesh quality consequences of pre-mortem crowding stress in Atlantic mackerel (Scomber scombrus)

In commercial wild capture pelagic fisheries it is common practice to crowd catches to high densities to allow efficient pumping onboard. Crowding during the final stages of purse seine capture for small pelagic species often results in intense and sustained behavioural escape responses. Such a response may trigger a shift in energy production from aerobic to anaerobic pathways and result in metabolic acid accumulation and exhaustion of intracellular reserves of ATP. Where there is insufficient time or opportunity to recover to physiological equilibrium before death, pre-mortem stress may be an important determinant of fillet quality, as has been shown for a variety of farmed fish species. However, there is currently a lack of knowledge related to the flesh quality implications of capture stress for wild captured species in European waters. Here we show that crowding results in a physiological stress response that has consequences for flesh quality in the wild captured species Atlantic mackerel (Scomber scombrus). Using small schools in tanks and aquaculture net pens in three separate experiments, we found crowding results in physiological changes in mackerel consistent with an acute stress response and anaerobic metabolism. Consequently, we found crowded fish had more acidic pre- and post-mortem muscle pH as well as indications of faster onset and strength of rigor mortis and increased cathepsin B & L activity. We examined fillet flesh quality after two and seven days of ice storage and found reduced green colouration, increased gaping (separation of muscle myotomes) and reduced textural firmness associated with fish which had been crowded. However, the effects on quality were dependant on experiment and/or storage time. These results indicate the potential of crowding capture stress to influence the flesh quality of an economically important species and may have important implications for the wild capture pelagic fishing industry.publishedVersio

Effects of capture-related stress and pre-freezing holding in refrigerated sea water (RSW) on the muscle quality and storage stability of Atlantic mackerel (Scomber scombrus) during subsequent frozen storage

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Electrical stunning and killing of Atlantic salmon

Source at https://nofima.no/publikasjon/2208193/.Atlantic salmon (Salmo salar) at various size 226-1938 g were placed in electric dry stunning either tailor head- first and then exposed to 50 Hz, 240 V AC for 0.5 and thereafter 9.5 s of electricity. This to verify whether the animal is rendered unconscious prior to killing by immersing the animal into cold brine (-14 to -18 °C) or hypoxic water, supersaturated with CO2. In addition, salmon from 2000 to 5000 g were exposed to head stunning only. Behaviour, heart (ECG) and brain (EEG) activity were monitored until animal was classed as dead. Post the treatment, the internal temperature of the animal was measured placing loggers into the neuro and heart cavity. The electric potential across the brain was also measured. A preliminary evaluation of the EEG and ECG registrations in the individual fish showed that loss of consciousness can be induced within 0.5 second and consciousness can be prolonged without recovery when the cold brine or seawater saturated with carbon dioxide is applied as killing method. Our results also suggest that the current can be applied head to tail, which facilitates immediate stunning of Atlantic salmon in a commercial setting. We conclude that electrical stunning in combination with cold brine is effective for humane stunning and killing Atlantic salmon

Extending the Shelf Life of Atlantic Salmon (Salmo salar) with Sub-Chilled Storage and Modified Atmosphere Packaging in Recyclable Mono-Material Trays

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Using renowned chefs for VeriTaste™ as a sensory method analysis in food products – A comparison of Atlantic salmon stored in refrigerated seawater and on ice

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The effect of alternate-day feeding on growth and feed conversion in Atlantic cod Gadus morhua

This study aimed to investigate the effect of alternating feeding (Alt) compared with control being fed every day (Con) in the on-growth face of Atlantic cod. Individually marked fish (198 and 98 in the Con and Alt groups, respectively) was sampled for weight and length on 6 occasions over a 15-month period, where mean weight increased from 628 and 758 g to 2635 and 3041 g, for the Con and Alt groups, respectively. Feeding alternate day resulted in 13 percentage more weight gain in the alternating feeding group (2283 vs. 2007 g) and improved feed conversion ratio (FCR, 1.07) compared with control (FCR 1.45). The Alt group consumed significantly less feed (27%) compared with control. The results demonstrate that feeding costs can be drastically reduced without compromising biomass growth by using feeding on alternate days during the on-growing period of Atlantic cod.publishedVersio