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.
