In ETHIQUAL, the development of new technology makes it possible to measure whether the fish are thriving in the fish farm. The equipment, called SmartTag, is attached to the fish and measures how often and how much the pressure changes in the mouth, and thereby monitoring the respiration of individual fish. From the tag, audio signals are sent to an under-water microphone, forwarding it to a computer where a programme calculates the breathing activity. Previous and ongoing laboratory studies have demonstrated that breathing activity is a good welfare indicator in fish, responding both to variation in water quality and to other types of stressors. In the future, fish farmers may monitor their fish by having a certain number with this equipment in e.g. the net cages. Abnormal breathing activity indicates something is wrong, and measures can be implemented.
Results from a pilot study with Atlantic cod showed that intensive rearing conditions, like high stocking density, low specific water flow, hypoxic or hyperoxic conditions, affects growth, feed intake, physiology and health of juvenile Atlantic cod, indicating negative consequences for the welfare status.
The studies of carp represent new knowledge about ethical qualities in fish, both regarding husbandry and pre-slaughter conditions. In a series of carp studies, the most important results have been the clear demonstration that, in carp as in many other species of animals, individual fish show marked and consistent variation in behavioural and physiological responses to environmental challenge.
In a series of slaughter experiments, it was demonstrated that immediate and permanent loss of consciousness and sensibility in carp can be achieved after 10 second electrical stun (7.3 ± 1.1 V/cm and 0.14 ± 0.03 A/dm2 at a conductivity of 200 µS). Carp was chilled in flake ice or on ice slurry for 15 min. During the entire storage period of the fillets pH values were higher after electrical stunning (p < 0.05), compared to the commercial method (30 min asphyxia followed by a blow on the head). To assess the effect of a short-term stressor on cortisol, glucose and lactate plasma levels in turbot, blood sampling should be carried out 30 min post stress. It was observed that transport may lead to an increase in blood plasma concentrations of cortisol, glucose and lactate in turbot. Transport may also influence the evolution of rigor mortis in turbot significantly.