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.

Most studies carried out with seabass under self-feeding conditions report an intriguing social structure that is built around the device and the food dispenser with three coexisting triggering categories: hightriggering (HT), low-triggering (LT) and zero-triggering (ZT) fish. However, neither sex nor feeding motivation or hierarchy can explain the establishment of this specialization. We characterised the personality of seabass with the commonly used restraint and open field tests and assessed the link between personality traits and individual triggering activity towards the self-feeder apparatus. We found no differences between triggering categories during the restraint test but high triggering fish were characterised as shyer than low-and zero-triggering fish during the open field test. Triggering activity was negatively correlated with exploratory capacities and boldness. This experiment provides for the first time evidence that high triggering status in seabass is correlated with personality traits, which could partly explain the social structure that builds around a self-feeder device. Highlights►European seabass personality (i.e. bold-shy and motivation to escape stressful situation) was characterized. ►Latency to emerge from a shelter and latency to escape during a restraint test were correlated. ►Placed under self-feeding, individual triggering activity level was higher in shy individuals.

To understand the genetic basis of coping style in European seabass, fish from a full factorial mating (10 females x 50 males) were reared in common garden and individually tagged. Individuals coping style was characterized through behavior tests at four different ages, categorizing fish into proactive or reactive: a hypoxia avoidance test (at 255 days post hatching, dph) and 3 risk-taking tests (at 276, 286 and 304 dph). We observed significant heritability of the coping style, higher for the average of risk-taking scores (h2 = 0.45 ± 0.14) than for the hypoxia avoidance test (h2 = 0.19 ± 0.10). The genetic correlations between the three risk-taking scores were very high (rA = 0.96–0.99) showing that although their repeatability was moderately high (rP = 0.64–0.72), successive risk-taking tests evaluated the same genetic variation. A mild genetic correlation between the results of the hypoxia avoidance test and the average of risk-taking scores (0.45 ± 0.27) suggested that hypoxia avoidance and risk-taking tests do not address exactly the same behavioral and physiological responses. Genetic correlations between weight and risk taking traits showed negative values whatever the test used in our population i.e. reactive individual weights were larger. The results of this quantitative genetic analysis suggest a potential for the development of selection programs based on coping styles that could increase seabass welfare without altering growth performances. Overall, it also contributes to a better understanding of the origin and the significance of individual behavioral differences.

Although individual electronic tagging using PIT (Passive Integrated Transponder) tags is well established, it is mainly used for fish > 60 mm in length. Since electronic tagging is an ideal identification method, we used RFID (Radio Frequency Identification) microtags (6 mm in length, 1 mm in diameter, 10 mg in mass) to characterize individual fish from the early stages of their development and throughout their lifecycles. We used sea bass, Dicentrarchus labrax (105 day-old fish weighing between 100 and 1100 mg), and studied the effects of intra-coelomic tagging in half the population using different endpoints including survival and tag reading, growth over 6 months and swimming responses. Dead fish were counted daily, biometric data were collected at 21 to 28 days intervals and fish were sexed at the end of the experiment. Behavioral swimming responses following a sudden dark challenge were evaluated after the first three biometric measurements (immediately after tagging, and then 21 and 42 days later). After 6 months, mean survival was 69%, the smallest surviving fish weighed 197 mg at tagging, and success in tag reading was 79% for the size class 300-400 mg after 63 days. No negative effects were observed on growth and most deaths occurred within 15 days after tagging with a first peak after 5 days but that did not particularly affect the smallest individuals. Differences in swimming responses were detected between tagged fish and untagged controls immediately after the surgical procedure with tagged fish swimming more than controls for 45 min. However, after 21 days, the tagged fish swam less than the untagged controls after being placed in the observation tank for 1 h and 45 min. At 42 days post-tagging, no further differences were observed. Overall, results suggested that the tagging method was suitable for fish as small as 400 mg and 36 mm in total length. This type of early tagging method is invaluable for the longitudinal monitoring of individual biological traits (e.g., growth) or for repeated assays with the same individual at distinct time points (e. g., behavior studies). We used it for a first evaluation of early growth differentiation between sexes and demonstrated a 31% mass gain difference in females that was visible as soon as the fish reached 105 days old. This confirms the potential of the method for the selection of early-expressed character traits which could lead to rearing cost savings for the aquaculture research field. (C) 2014 Elsevier B.V. All rights reserved

Individual stress coping style (reactive, intermediate and proactive) was determined in 3 groups of 120 pit tagged European seabass using the hypoxia avoidance test. The same three groups (no change in social composition) were then reared according to the standards recommended for this species. Then, 127 days later, individuals initially characterized as reactive, intermediate or proactive were submitted to an acute confinement stress for 30 min. Blood samples were taken to measure plasma cortisol levels 30 min (Stress30) or 150 min (Stress150) after the end of the confinement stress. Individuals were then sacrificed to sample the telencephalon in order to measure the main monoamines and their catabolites (at Stress30 only). Individuals from Stress150 were sampled for whole brain for a transcriptomic analysis. The main results showed that reactive individuals had a lower body mass than intermediate individuals which did not differ from proactive individuals. The physiological cortisol response did not differ between coping style at Stress30 but at Stress150 when intermediate and proactive individuals had recovered pre stress levels, reactive individuals showed a significant higher level illustrating a modulation of stress recovery by coping style. Serotonin turnover ratio was higher in proactive and reactive individuals compared to intermediate individuals and a significant positive correlation was observed with cortisol levels whatever the coping style. Further, the confinement stress led to a general increase in the serotonin turnover comparable between coping styles. Stress150 had a significant effect on target mRNA copy number (Gapdh mRNA copy number decreased while ifrd1 mRNA copy number increased) and such changes tended to depend upon coping style. Highlights► Reactive fish showed a slower stress recovery after acute confinement stress ► Serotonin turnover ratio was affected by acute confinement stress ► A positive correlation was shown between plasma cortisol and serotonin turnover ratio