Coping styles in European sea bass: The link between boldness, stress response and neurogenesis

Abstract

Coping styles consist of a coherent set of individual physiological and behavioral differences in stress responses that are consistent across time and context. Such consistent inter-individual differences in behavior have already been shown in European sea bass (Dicentrarchus labrax), but the associated mechanisms are still poorly understood. Here, we combine physiological measurements with individual behavioral responses in order to characterize coping styles in fish. Fish were tagged and placed in a tank for group risk-taking tests (GRT) at 8 months of age to evaluate boldness using the proxy latency of leaving a sheltered area towards an open area. A subsample of these fish were individually challenged 16 months later using an open field test (OFT), in which the boldness was assessed after being placed in a shelter within an open arena. Latency to exit the shelter, time spent in the shelter, and distance travelled were recorded for this purpose. The blood and brain were then collected to evaluate plasma cortisol concentration and neurotransmitter levels (dopamine, norepinephrine, serotonin, and related metabolites), as well as brain transcription of key genes involved in stress axis regulation (gr1, gr2, mr, crf), neurogenesis (neurod1, neurod2, pcna), and neuronal development (egr1). Fish acting bolder in the GRT were not necessarily those acting bolder in the OFT, highlighting the relatively low consistency across different types of tests performed with a 16-months interval. There was, however, a significant correlation between stress markers and boldness. Indeed, mRNA levels of mr, crf, gr2, egr1, and neurod2, as well as norepinephrine levels were higher in shy than bold fish, whereas brain serotonergic activity was lower in shy fish. Overall, our study highlights the fact that boldness was not consistent over time when testing context differed (group vs. alone). This is in agreement with previous literature suggesting that social context play a key role in boldness measurement and that the particular life history of each individual may account in shaping the personality fate of a fish. Highlights ► Boldness is not consistent when characterized using different types of test over an interval period of 16 months (group vs. individual tests). ► After open field test, plasma cortisol concentration is similar between bold and shy fish. ► Shy fish, however, display higher level of transcription of mr, gr2, crf, egr1 and neurod2 (trend) and also higher level of norepinephrine and lower turnover ratio between serotonin and its main metabolite (hydroxyindoleacetic acid) in the whole brain.

Surgical implantation of electronic tags does not induce medium-term effect: insights from growth and stress physiological profile in two marine fish species

“…Our results confirm that tag implantation does not induce chronic stress in either the sea bream or the sea bass, as observed in various other fish species [25,29]. It is thus important to emphasize that tag implantation does not exert longterm adverse effects on a high-stress responder species such as the European sea bass [30][31][32].…”

Surgical implantation of electronic tags does not induce medium-term effect. Insights from growth and stress physiological profile in two marine fish species

“…Our results con rm that tag implantation does not induce chronic stress in either the sea bream or the sea bass, as observed in various other sh species [25,29]. It is thus important to emphasize that tag implantation does not exert long-term adverse effects on a high-stress responder species such as the European sea bass [30][31][32].…”

Consistent individual competitive ability in rainbow trout as a proxy for coping style and its lack of correlation with cortisol responsiveness upon acute stress

“…particularly when the consistency is tested across long periods or when the conditions of the fish change between tests [25,44]. In general, the consistency seems to vary depending on the species, the trait evaluated, the test used and the environmental conditions previously or during the tests.…”