Unpredictability in food supply during early life influences growth and boldness in European seabass, Dicentrarchus labrax

•Early and recent experience is an important driving force shaping boldness in European seabass.•Predictable food supply induced faster growth and fish became shyer than fish reared under an unpredictable food supply.•Predictable feeding time should be respected when assessing essential physiological functions such as growth and behavior. Biological variability is no longer considered as statistical noise, but rather as an adaptive benefit. This variability comes from consistent differences in behavioral and physiological responses among individuals to a changing/challenging environment, named “coping style”, “temperament” or “personality”. Many studies have described how to characterize personality traits and how to assess their consistency over time and between different contexts; however, little is known about the environmental factors shaping personality development. Because contrasting personalities are maintained with evolution, this lead to the widespread assumption that genes play a predominant role in personality. In many cases, personality traits are however also likely to be determined by individual experience, which is probably at least as important as genetics in shaping personality. The aim of this study was to assess how environmental variability (herein food predictability) impacts behavioral responses, particularly the shyness-boldness axis, one of the most widely shared animal personality trait. Here, we reared juvenile seabass (95days old) from two divergent strains selected for feed deprivation tolerance under standard conditions for 40days. Thereafter, we submitted them to two feeding treatments (Predictable versus Unpredictable) starting at 135 dph and lasting 60days. Seabass reared under a predictable food supply (PFS) grew faster and were shyer than fish reared under an unpredictable food supply (UFS) (i.e. they took more time to exit the refuge zone of a Z-maze; UFS: 132.47±34.63s; PFS: 336.79±56.97s) but their exploration tendency was similar. We also examined the behavioral responses of these fish facing a hypoxic challenge. Hypoxia tolerance results were consistent before and after the two feeding treatments. Our findings show the importance of early environmental experience as a driving force shaping boldness. In addition, we provide further evidence that predictable feeding time should be respected in studies assessing essential functions such as growth and behavior. Although personality traits are partially heritable, this st