Forsøksdyr: Capture Related Stress in Mackerel


Godkjenningsdato 23.08.2018

In Norway, 1.3 million tonnes of fish were landed by commercial purse seiners in 2017. However, during the capture and slaughter process, fish are exposed to stresses such as crowding, hypoxia and rapid temperature change. Such stressors have the potential to negatively impact upon the animals short and long-term welfare.

The purpose of these experiments is to increase our understanding of how current purse seine capture and slaughter practices affect the behaviour, physiology and resulting meat quality of Atlantic mackerel (Scomber scombrus). Mackerel supports an important purse seine fishery in Norway, but is a delicate species that is highly susceptible to stress. By understanding how mackerel responds to stress we hope to promote welfare friendly fishing practices that maximise: 1) survival potential if the catch is to be released and: 2) meat quality if the catch is to be retained, contributing towards a more environmentally sustainable and profitable Norwegian fishing industry.

This application is in support of the FHF project “Fangstkontroll in Notfiske”. Three replicates of four small schools of mackerel (consisting of 40 individuals) will be exposed to typical purse seine capture stressors of either hypoxia (< 40 % oxygen saturation at ~8°C), crowding (using purse seine netting, up to densities of 50 fish per m3), crowding and hypoxia together or a control, for short durations (10 minutes). Resulting behavioural, physiological and meat quality responses will be determined, using camera observation, as well as blood, tissue and meat quality sampling. The effect of slaughter method on meat quality will also be investigated after stressor treatments for two mackerel schools of 15 fish. Slaughter methods investigated will be: 1) a blow to head followed by brain spiking; 2) immersion in cold hypoxic seawater and 3) electrical stunning followed by immersion in cold hypoxic seawater. These experiments will also be replicated three times. Optimal field strength and duration for effective mackerel electrical stunning will be determined by examination of behavioural and reflex responses on 25 fish post stunning. In addition, swimming metabolism (in 30 fish) and hypoxia tolerance (in a further 30 fish) of individual mackerel will be tested in respirometers. Therefore, the number of mackerel involved in all experiments will total 655.

Simulation of commercial conditions during capture and slaughter of pelagic fish can be regarded as “Considerable distress” as fish are exposed to hypoxic environments, rapid temperature changes and crowding to relatively high densities, inducing a level of distress and perhaps death. As we intend to study physiology and behaviour, there is no replacement for the use of live animals. We have therefore focused on reducing the number of animals required to an absolute minimum, by use of power analysis. Furthermore, as much data as possible will be collected from each experimental subject. The project will also reduce the severity of the experiments by avoiding chronic and acute pain, by defining early stage endpoints. For the development of effective future legislation, these experiments are required in order to reveal, understand and compare current animal welfare practises in commercial fishing.