Project 5.2 ETHIQUAL

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

Major achievements in 2007

The Atlantic cod studies in 2007 have focused on the effects of acute and chronic stress and how this affects ethical quality traits and muscle quality traits of the product. Atlantic cod shows a characteristic acute stress response with an increase in plasma cortisol and marked changes in metabolisation of carbohydrates, lipids and proteins. Compared to salmonids, the Atlantic cod generally showed less acute stress responses during a high density pre-slaughter handling. Plasma cortisol increased soon after an acute stress, and there were minor differences in cortisol levels between different pre-slaughter treatments. Prolonged stress before slaughter led to metabolic changes, e.g. in lactate and glucose. These physiological changes led to measurable differences in product quality traits.  



In the studies of carp, our survey of working carp ponds has shown marked effects of husbandry-induced stressors on the ethical quality of farmed fish. For example, body condition falls and incidence of fungal infection rises after spring grading. In addition, we have shown that carp with different coping strategies show strikingly different responses when such stressors are manipulated experimentally. Fish with a reactive coping strategy sustain higher growth rates under oxygen stress than do those with a proactive strategy. They also show different growth strategies, with reactive fish gaining in weight rather than length at low temperatures. Most importantly, studies at the molecular level have shown that patterns of change gene expression in response to stressors are different, and often in opposite directions, in practise and reactive fish. Besides being of specific relevance to ethical quality in farmed carp, this last result demonstrates how screening for coping strategy prior to differential gene expression studies can help to explain the high variation between individuals that is commonly reported and can uncover important effects of environmental challenge on gene expression that would otherwise have passed unnoticed.



Based on earlier results showing that feeding behaviour is a major indicator of adaptation potential and welfare, we have continued to test different strains of sea bass. Besides, other behavioural and physiological variables have been examined to highlight differential feed demand rhythms and wastage behaviour. First, risk taking tests were carried and showed that sea bass of the wild strain displayed faster risk taking behaviour with less homogeneity in time than those of the Massal strain. It thus seems that Massal was capable of a slower learning but it was more durable in time. This ability could be a benefit for that strain which will be potentially less sensitive to different stresses present in the rearing environment. Second, sea bass from the domestic, wild and Massal strains were tested for their individual oxygen consumption. Results suggested that (i) physiological functions were equivalent between the strains and consequently (ii) that the selection of the Massal strain, based on production traits respects its functional integrity and (iii) that sea bass possess a large physiological plasticity. Third, a comparison of individual abilities of sea bass to trigger the self-feeder with actual feed intake was measured (X-ray method). This study indicated that a feeding hierarchy might exist within sea bass individuals fed with a demand-feeder. That hierarchy might be based on the relationship between feed intake and fish size (i.e. scrambling around pellets) rather than based on competition about the feeder-trigger.



Three methods for stunning were applied on carp at the premises of the Polish SME Carp-Pas to study their effects on product quality parameters. Two experimental methods, viz. percussion by using a modified air nailer (developed by IMARES) in combination with chilling for 15 min in flake ice and electrical stunning by applying 400 V a.c. for 5 s in combination with chilling (developed by RIVO and ID) for 15 min in flake ice, were compared to the current industrial method for killing. The industrial method consists of asphyxia for 30 min in combination with manually applied blow on the head. RIVO performed analysis of onset and resolution of rigor mortis in the gutted carp and analysis of colour (L, a and b values) of fillets. In a paper published in 2007, we described that not all carp were unconscious after percussive stunning. Therefore, it is judged that this method cannot be used, as there is no certainty for immediate loss of consciousness and sensibility. For turbot two approaches were tested to ease the stress generated during manipulation of fish inspired from what happens in industry when fish are transported. The first approach was to maintain turbots in the water during transfer operations, unlike what often takes place in industrial practices. The second one consisted in decreasing the salinity of water containing turbots on the point to be stressed in order to lessen the energy expended for restoring the hydromineral balance disrupted by stress. In-water transferring of turbots seemed to be as stressful as netting the fish and lowering the salinity had no effect on the stress in turbots turned upside down for 10 min. However, transport of turbots in water of 24 ppt may not significantly increase the cortisol level in the fish, compared to non transported turbots, transport in 29 ppt water did.


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 IFREMER student visits Fiskeriforskning for training 09-05-07

As part of the SEAFOODplus training programme PhD student Sandie Millot and her supervisor Marie-Laure Bégout from IFREMER visited Fiskeriforskning in Tromsø for aquaculture studies