For years, even centuries, personality has been studied in humans. In 1990, five temperaments (openness, conscientiousness, extraversion, agreeableness, and neuroticism) were defined and are now used to describe human personality. These characteristics have also been identified in numerous terrestrial animals, particularly in agricultural environments such as cattle or pig farms, in order to obtain performance or animal welfare indicators.
In animals, personality has been divided into five traits: shyness and boldness (in response to high-risk situations), exploration (in response to novel situations), activity level, aggression, and sociability. These characteristics are often linked and are then called behavioral typologies.
There are two extreme types of responses, and individuals within a population are distributed between these two extremes along a spectrum. There are the more proactive individuals who exhibit a fight or flight response and, on the opposite end of the spectrum, the predominantly reactive individuals who exhibit a freeze response and demonstrate significant shyness.
Initially demonstrated in birds or mammals, these responses lead for example to the observation that a more proactive pig quickly explores its environment and forms routines (it always moves very quickly in the same corridor to look for food), while a more reactive individual will explore the environment thoroughly, will tend to change direction more frequently and will find food more quickly if it changes corridors in a maze.
Is this fish shy or bold?
I have been observing fish for over thirty years, particularly their behavioral responses and their ability to adapt to different environments. Also in their case, work carried out in the laboratory or in the natural environment for more than two decades has helped to demonstrate that, like all animals, fish are endowed with complex cognitive, learning and memory capacities: fundamental skills for their intelligence.
These abilities allow them to solve the problems they encounter in order to survive in their natural and social environments and, like all animals, the way in which they solve these problems varies depending on their personality, whether it is more shy or bold. The existence of behavioral patterns corresponding to the two proactive/reactive typologies has been widely demonstrated in fish, whether in a breeding context or in an ecological context.
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A prerequisite for this research in general, and for the one I carried out in particular, was the development of experimental devices to measure these personality traits adapted to social animals like fish, to the aquatic environment and to the methods available. In particular, it is important to carefully design the test setup and procedure to avoid ambiguities.
In some cases, for example, we want to measure patterns of behavior or level of anxiety in response to a stressor, and there are tests for this, such as placing the individual in a new environment and immediately measuring their response (swimming activity).
Mazes and arenas for observing fish
In other cases, when one wishes to measure a characteristic other than the response to a stressor, the simplest method is to add an acclimation period that is not used to measure the behavioral characteristic of interest. In my laboratory, we have several devices to measure the behavioral capacities of fish (such as medaka, zebrafish or sea bass) during challenges or after exposure to chemical molecules or to situations simulating climate or global changes.
These devices include mazes, location preference devices (in which fish can choose between a light or dark background in their aquarium), and observation arenas (large aquariums suitable for small groups of fish), in which the fish are filmed and then their movements analyzed using specialized software.
Thus, to characterize personality traits, that is to say individual characteristics, experiments were first generally carried out with individuals tested in isolation. By adapting tests developed for rodents, we are studying, for example, the exploration of a Z-maze by marine fish (medaka, sea bass) based on 2D video recordings of their movements.
An individual is placed in a shaded starting area and, after a few minutes of acclimatization, a portal opens remotely, allowing exploration of four continuous corridors without any particular reward. This test evaluates both boldness in risk-taking (exiting the protected space) and exploring a new environment.
This allowed us, for example, to show that the fish’s previous life experience (being fed at fixed or unpredictable times) influenced the level of boldness: being fed at fixed times made individuals less bold.
In another context, that of ecotoxicology, this also made it possible to demonstrate that pollutants could alter the boldness, activity and exploratory capacities of fish exposed to certain pollutants or of their offspring.
However, the handling of each individual tested constitutes a source of stress that can reveal and alter behavioral responses and cognitive abilities. To mitigate this, we also recorded swimming activities in small groups of 6-10 individuals. This allows us to measure the behavioral response of individuals within the group.
In addition to the intensity of the activity, the distances between the fish and their use of space in this new environment are indicators of stress and anxiety. With this approach, we evaluate activity, thigmotaxis (repeated movements of an individual that follows the walls and avoids the center of the aquarium) and group cohesion. In this test, the central zone is also a more exposed area, favored by bold fish _ and avoided by shy or anxious fish.
To differentiate between multiple behavioral characteristics in a single test, it may be necessary to perform multiple tests and ensure consistency of responses. For example, a decrease in oxygen availability increases tigmotaxis while reducing group activity and cohesion. These indicators, associated with blood measurements of stress markers, such as cortisol, make it possible to qualify the level of animal well-being.
Knowledge essential to well-being
Still in a group, we were among the first to measure boldness and individual activity in very large groups, from 500 to 1500 measurements. To do this, we installed a separator in the 5 m³ breeding tanks with a circular passage of 10 cm in diameter in the middle.
Each fish equipped with an electronic chip has its identity read by an antenna when it leaves the group in the shaded area and ventures to the other side of the partition. By repeating the same test three times, several weeks apart, this research demonstrated that there was learning – memorization – that personality traits remained stable over time and that shyer individuals obtained better results under the conditions of our fish farm.
Indeed, animal well-being is defined by the French Agency for Food, Environmental and Occupational Safety (ANSES) as a positive mental and physical state, linked to the satisfaction of its physiological and behavioral needs, as well as its expectations. This state varies depending on the animal’s perception of the situation.
These various examples show how, by developing suitable observation methods, measuring behavioral responses makes it possible to see fish differently, to reveal and demonstrate their needs and expectations, their sensitivity and their cognitive abilities, and to overcome the “goldfish memory”. Rethinking the place of animals and fish in our societies is one of the essential steps to understanding and preserving fish in all their biodiversity, including their behavior, in a context of proven global changes.
A big thank you to all the students and colleagues who developed these studies alongside me.
This text was published in The Conversation in French. Click here to read the original version
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