Major achievements in ETHIQUAL

Ethical quality traits in farmed fish: The role of husbandry practices and aquaculture production systems

Major achievements in 2006

The research in ETHIQUAL has generated many interesting results. The acute stress response in farmed Atlantic cod has been identified by examining cortisol and metabolic changes in blood after handling stress. In a study where full-sibling families of coastal and migratory cod have been screened for differences in individual behavioural traits such as boldness, it was demonstrated a difference between families in the willingness to expose themselves for novel environments, and this behavioural trait is important in the selection for stress-tolerance in farmed fish species. The ability of cod to detect differences in water quality and possible avoidance and preference responses have also been studied and the results indicate that cod respond physiologically to changes in water quality in order to maintain homeostasis, but the fish have probably a limited behavioural response to short-term non-lethal changes in e.g. CO2. The studies on the relationships between intensive rearing conditions, flesh quality and ethical quality have generated new data. The results indicate that husbandry conditions such as high fish density and poor water quality may lead to reduced welfare and thereby, reduced ethical quality. Juvenile cod subjected to high fish density and low specific water flow, and subsequently high CO2, showed reduced growth and higher incidences of nefrocalsinosis. The fish was followed for over one year in sea cages. In this period, the fish grew according to a cod growth model. During the sea cage period we tested the non-invasive telemetry equipment ("SmartTag") twice to monitor breathing rhythm after handling stress. In two other experiments, the deviation from the control group in growth, survival and health indices suggest that the welfare of juvenile cod can be diminished by hypoxic or hyperoxic conditions. It was also found that the transcription levels of the antioxidant genes, Cu/Zn superoxide dismutase (SOD) and phospholipid hydroperoxide glutathione peroxidase (GSH-Px) and the stress gene CYP1A were significantly different in fish exposed to either hyperoxia or hypoxia, compared to the normoxia group.


In the studies of carp, it has been demonstrated that the fish show marked and consistent individual differences in behavioural and physiological responses to challenge (or different ‘coping strategies’). These differences contribute to the ethical quality of farmed carp. It has also been demonstrated marked effects of a number of husbandry practices and seasonal changes in water quality on the ethical quality of farmed carp. Finally, it has been shown that molecular tools based on differential gene expression can be combined with conventional indicators to give a fuller characterisation of ethical quality in carp.


In sea bass, the link between feed demand, growth and physiological variables show that feeding behaviour is a major indicator of welfare. In a study where a computerized on-demand feeding system coupled with a PIT tag monitoring device was used to continuously record the triggering activity, it was found that 89% of the fish actuated the trigger, but only two or three fish accounted for 64% of the total triggering activity. These few high-triggering individuals did not exhibit a higher initial and final body weight or a higher specific growth rate than low and zero triggering fish, but at the time an individual was the high-triggering fish in the tank, its growth increased and was higher than that of the other fish. In some other experiments with two sea bass strains it was found a growth rate difference between strains and a differential feed demand rhythm and wastage behaviour.


In a series of slaughter experiments, it was observed that common carp is effectively stunned by head-only electrical application with 0.24 ± 0.03 A (~ 160 V) and in fresh water with a current of  0.14 ± 0.03 A/dm2  (~ 115 V) for 1.2 s at a conductivity of 200 µS of the water after which they recover. Since not all carp were unconscious after percussive stunning, it is judged that this method can be used, but there is no certainty for immediate loss of consciousness and sensibility. Stunning and killing turbot directly at the fish farm can reduce stress in the fish at the time of slaughter, because stress due to transport is avoided. Analysis of the colour of the fillets showed that experimental method (electrical stunning followed by chilling) after transported resulted in a slightly more bluish than the non-transported batch that was killed by the experimental method. For fish stunned and killed by the industrial method (live chilling), transport resulted in a lower pH of the flesh, compared to the non-transported batch. During experimental stunning and killing method electrostimulation of the muscle tissue may have masked the effect of transport on onset of rigor mortis and evolution pH.

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Considering animal welfare when harvesting fish from aquaculture 08-10-06 
SEAFOODplus is considering both animal welfare and product quality when harvesting fish from aquaculture. Methods have been developed with common carp where the fish is rendered unconscious without any suffering prior to killing, while a high product quality is retained.

Projectleader ETHIQUAL

Dr. Hilde Toften