Size-selective harvesting impacts learning and decision-making in zebrafish

Size-selective harvesting common to fisheries is known to evolutionarily
alter life-history and behavioural traits in exploited fish populations.
Changes in these traits may in turn modify learning and decision-making
abilities through energetic trade-offs with brain investment that can vary
across development or via correlations with personality traits. We
examined the hypothesis of size-selection-induced alteration of learning
performance in three selection lines of zebrafish (Danio rerio) generated
through intensive harvesting for large, small and random body-size for
five generations followed by no further selection for ten generations that
allowed examining evolutionarily fixed outcomes. We tested associative
learning ability throughout ontogeny in fish groups using a
colour-discrimination paradigm with a food reward, and the propensity to
make group decisions in an associative task. All selection lines showed
significant associative abilities that improved across ontogeny. The
large-harvested line fish showed a significantly slower associative
learning speed as subadults and adults than the controls. We found no
evidence of memory decay as a function of size-selection. Decision-making
speed did not vary across lines, but the large-harvested line made faster
decisions during the probe trial. Collectively, our results show that
size-selective harvesting evolutionarily alters associative and
decision-making abilities in zebrafish, which could affect resource
acquisition and survival in exploited fish populations.