Individual differences in physiological and behavioural responses to stressors are increasingly recognised as adaptive variation and thus raw material for evolution and fish farming improvements including selective breeding. Such individual variation has been evolutionarily conserved and is present in all vertebrate taxa including fish. In farmed animals, the interest in consistent trait associations, that is coping styles, has increased dramatically over the last years because many studies have demonstrated links to performance traits, health and disease susceptibility and welfare. This study will review (i) the main behavioural, neuroendocrine, cognitive and emotional differences between reactive and proactive coping styles in farmed fish; (ii) the methodological approaches used to identify coping styles in farmed fish, including individual (group) mass-screening tests; and (iii) how knowledge on coping styles may contribute to improved sustainability of the aquaculture industry, including welfare and performance of farmed fish. Moreover, we will suggest areas for future research, where genetic basis (heritability/ epigenetic) of coping styles, and the neuroendocrine mechanisms behind consistent as well as flexible behavioural patterns are pinpointed as central themes. In addition, the ontogeny of coping styles and the influence of age, social context and environmental change in coping styles will also be discussed.

Recent years have seen a growth of interest in the consistent differences in individual behaviour over time and contexts constituting so-called "individual coping styles". An understanding of this inter-individual variation is essential to improve our knowledge of the adaptive value of behaviour. Coping styles may have implications in diverse fields, so the development of appropriate screening methods for each species appears to be the most effective way to extend our knowledge and to incorporate behavioural responses into selection-based breeding programmes, to improve the domestication and welfare of farmed fish. We tested 30 juvenile seabass (Dicentrarchus labrax) at least twice in individual-based tests (feeding recovery in isolation, aggressiveness, exploration in a T-maze and net restraint) and group-based tests (risk-taking and hypoxia sorting), to assess coping style consistency in the short and long term and between tests. The results of individual-based tests were inconsistent over time and between tests in our setup: the time between repeat tests, learning and species-specific behavioural responses appeared to have a major impact. By contrast, the results of group-based tests, such as risk-taking and hypoxia sorting, appeared to be consistent (both in the short and long term). These tests therefore appeared to be the most relevant for the characterisation of coping style in European seabass. Furthermore, the results of these tests were also predictive of cortisol stress response. These tests are simple to perform and can be used to screen large numbers of fish, the first step in selection programmes including behavioural profiles Highlights ► We characterized coping styles in European seabass.► We showed evidence for behavioural consistency in group based tests.► Results may also be accounted for by species specificity in behavioural responses.

SUMMARYPiranhas are known to be sound-producing animals. Nevertheless, the biological significance of piranha calls remains unclear because sounds have been recorded only when specimens were held by hand or trapped in a gill net. These sounds are generated by rapid contractions of sonic muscles that insert on a broad tendon surrounding ventrally the cranial sac of the swimbladder. The piranha swimbladder is thought to play an important role in sound production as an impedance-matching device and as a resonator. However, the vibratory capacities of the cranial and caudal sacs and the exact role of both sacs in sound production remain poorly understood. In this study, three sounds were each associated to a specific behaviour. The first sound (type 1) was produced during frontal display; it had numerous pulses and lasted 140±17ms, with a fundamental frequency of 120±4Hz. It corresponded to the sound made by hand-held fishes. The second sound (type 2) was produced during circling and fighting behaviour; it was a single pulse lasting 36±8ms, with a fundamental frequency of 43±10Hz. The third sound (type 3) corresponded to chasing behaviour and comprised three to four pulses, each lasting 3±1ms, with a fundamental frequency of 1739±18Hz. Using a laser vibrometer to study the swimbladder displacement when stimulated at different frequencies, it was demonstrated that the first two sounds corresponded to the swimbladder mechanism. By contrast, the third sound was associated with the jaw mechanism. The vibrometer indicated that the swimbladder is a highly damping structure, simply copying the sonic muscle contraction rate. This study provides two interesting insights. First, it shows the relationships between three kinds of piranha sound and three specific behaviours. Second, using muscle stimulation at different rates, it shows which simultaneous conditions are required for production of sound in this species. Swimbladder calls were produced by a muscle contraction rate of approximately 100Hz because this periodicity allowed the swimbladder to vibrate. At this frequency range, the contraction-relaxation cycles of the swimbladder muscles engendered wall displacements that had short amplitudes and with only a small variability between them.

Feeding motivation is one major indicator of fish welfare and an investigation on the link between feed demand, growth and physiological variables in sea bass juveniles was developed. A computerized ondemand feeding system coupled with a PIT tag monitoring device was used to continuously record for 219 days the triggering activity of 150 individuals (initial average body weight 131.6 ± 1.80 g and coefficient of variation 16.8%). Each group was held in 400 l tanks at 22.2 ± 1.5 °C and light regime was 16:8 LD. In all the tanks, 89% of the fish actuated the trigger, but only two or three fish accounted for 45% of the total triggering activity. These few high-triggering individuals had a transient higher growth i.e. at the time an individual was the high-triggering fish in the tank, its Specific Growth Rate (SGR) increased and was higher than that of the other fish. However, high-triggering fish did not exhibit a higher initial and final body weight nor a higher average SGR than low-and zero-triggering fish. Fish of different triggering categories did not show differences in physiological variables (muscle composition, blood and tissues biochemistry). This study also revealed that when an imbalance between apparent daily feed tank consumption and feed demand was observed (i.e. wastage), it was mostly due to an increasing demand rather than a decreasing consumption; such wastage could often be linked to particular stressors (measuring day, population sampling or social interactions) and therefore, feeding motivation disturbances could be a relevant operational fish welfare indicator.