Why some fish grow faster than others: examining the interplay between metabolic phenotype, predator threat and growth performance

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All animals must acquire food for energy, but there is a vast diversity in how different species and even different individuals approach this task. Individuals within a species appear to fall along a bold-shy continuum, whereby some fish acquire food aggressively and with seemingly high risk, while others appear more opportunistic and cautious. Greater food consumption generally results in faster growth, but only if the energy acquired through food is more than enough to compensate for heightened metabolism associated with a more active lifestyle. Fast-growing phenotypes also tend to have elevated baseline metabolism – at least when food is plentiful – which further complicates the link between food consumption and growth. The net energy gained from a meal (as calculated from the specific dynamic action (SDA) coefficient) is optimised with larger meal sizes, but the digestion of large meals can erode the aerobic metabolic scope available for other critical activities such as predator avoidance. Thus, it is expected that fish in predator-rich habitats should regulate meal sizes to maximise growth efficiency without dangerously compromising aerobic capacity, and this balance may differ between individual metabolic phenotypes. This presentation will discuss these complicated interplays with a goal to better understand what drives intraspecific differences in growth performance.