Scientific Alert Note

Gene expression analysis reveals that temperament affects production and ethical quality of farmed carp

Many kinds of animals, including fish, show striking and consistent differences in how they respond to challenge. These differences are sometimes referred to as “temperament”. In common carp, a subset of fish are consistently active risk-takers while others are passive, risk-avoiders. Active carp have a higher resting metabolic rate than passive fish; they show a weaker physiological response to a standard stressor and different patterns of growth. When exposed to typical husbandry stressors, the two kinds of fish often show diametrically opposite responses in terms of which sets of genes are down-regulated or up-regulated. So temperament matters when it comes to production and ethical quality of farmed carp.


Authors: Felicity Huntingford and Sunil Kadri, Glasgow University, UK, Maciek Pilarczyk,  Polish Academy of Sciences, Poland and Simon Mackenzie, Autonomous University of Barcelona, Spain.




It is well known that many birds and mammals, individuals of the same species, gender and age often show striking and consistent differences in how they respond (behaviourally and physiologically) to challenges.  At one extreme, there are active, aggressive, risk taking animals with a high resting metabolic rate and an adrenaline-based stress response; at the other extreme are the more passive, risk avoiding, non-aggressive animals with a cortisol-based stress response and a low resting metabolic rate. These two types of animals do well in different environment types, which is why natural selection keeps them in the population. These differences are so striking, that they are sometimes described as “animal personalities”, but we prefer the term “temperament”.


It is becoming increasingly apparent that similar diversity is found in fish, although it is mostly for rainbow trout that differences in temperament have been studied at the physiological as well as the behavioural level. Now however, a group of researchers funded by SEAFOODplus in the project ETHIQUAL have shown that individual common carp also shows striking differences in response to challenge, at levels ranging from their behaviour, through their metabolism and stress physiology to their gene expression. We have also shown that this variation has important implications for production and ethical quality when carp is farmed.


Thus we find a subset of fish that, when faced with a potentially dangerous situation, are consistently quick to move about and explore and when faced with limited food are consistently active, pushy competitors (one cannot really accuse carp of being aggressive); we also find a different subset of fish that show the complete opposite response. The resting metabolic rate of active, risk-taking fish is almost 20% higher than that of their risk-avoiding counterparts. On the other hand, the expression of cortisol receptors in the brain and head kidney is strikingly higher in risk avoiding fish. 


Interestingly, these two kinds of fish show different patterns of growth, with the risk-taking fish tending to grow in length at the expense of condition and the risk avoiders putting on mass at the expense of growth in length. Gene expression studies tell us that, when challenged, the two kinds of fish often show diametrically opposite responses. For example, the gene for the cytokine TNFα is up-regulated in response to high temperature in risk taking carp, but down regulated in response to the same change in risk-avoiders.


In terms of scientific research, these effects of temperature on gene expression would have cancelled each other out and gone undetected had we not identified in advance the risk-taking phenotype of our carp. The fact that these different types of fish exist in farmed populations and that they respond differently to husbandry stressors is also important for SEAFOODplus’ aim of promoting aquaculture production while respecting consumer demand for ethically acceptable seafood.


From left: Felicity Huntingford, Maciek Pilarczyk, Simon Mackenzie and Sunil Kadri