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Welfare & health in sustainable aquaculture - AW1206

Unlike with land animals, it is extremely difficult for people who look after fish to determine whether they are ill or not. This is because the fish are underwater and often difficult to observe. Fish can be removed from the water, examined and if necessary sampled. However, this is a very stressful procedure for fish that can actually worsen their condition. The purpose of our research is to develop a non-invasive procedure that can be used by fish farmers to establish whether the welfare of their fish has been compromised.

The procedure is based on the well-known fact that, when fish are stressed, they produce a stress hormone - cortisol. What we have discovered is that some of this cortisol 'leaks' out of the gills into the water, from which it can be extracted and measured in a totally non-invasively way.

The concentration of cortisol in water is not only affected by stress (i.e. the amount of cortisol released by the fish) but also by the flow rate of the water, the biomass of the fish, their relative size range and temperature. When we carry out experiments in the laboratory, we can regulate all these factors. We can accurately measure the water flow rate and biomass in the tanks. We also can include appropriate control tanks that cancel out within-experiment effects of size range and temperature. However, in a commercial situation or in cage culture, this is very rarely possible. In order for us to be able to interpret a cortisol concentration taken from a commercial site, we need to find a compound that is released at a constant rate by fish, is modulated by fish size and temperature in the same way as cortisol BUT IS NOT affected by stress. By measuring this compound in water, as well as cortisol, we can hopefully normalise the concentration of cortisol so that it is independent of all factors but stress.

We have picked on melatonin because it is produced by fish at a constant rate during the night, appears to be affected only slightly (if at all) by stress and is released via the same route as cortisol (the gills). We reason that temperature and fish size will have parallel effects on the release rates of cortisol and melatonin. So far, this approach is looking very promising for salmon as well as trout.

We also want to look at creatinine as an alternative normaliser for cortisol concentrations. Creatinine is a product of muscle breakdown and is produced at a constant rate in most vertebrates. It is excreted via the urine (as opposed to the gills). However, the use of creatinine concentration in urine to normalise the concentrations of many other compounds is very common in medical practice. It has never been applied before to fish in the way that we are suggesting. However, we are the first group in the world to have been monitoring stress in fish by measuring cortisol in water! Creatinine concentrations will be much higher than those of cortisol melatonin (micrograms as opposed to nanograms per litre) and thus relatively easier to measure. There are many published procedures to aid us.
Project Documents
• EVID4 - Final project report : AW1206 final report   (424k)
Time-Scale and Cost
From: 2005

To: 2008

Cost: £194,528
Contractor / Funded Organisations
Animal Welfare              
Plants and Animals              
Fields of Study
Animal Welfare