In most fisheries, larger fish experience substantially higher mortality than smaller fish. Body length, life history, and behavioral traits are often correlated, such that fisheries-induced changes in size or life history can also alter

Size-selective mortality is common in fish stocks. Positive size-selection happens in fisheries where larger size classes are preferentially targeted while gape-limited natural predation may cause negative size-selection for smaller size classes. As body size and correlated behavioural traits are sexually selected, harvest-induced trait changes may promote prezygotic reproductive barriers among selection lines experiencing differential size-selective mortality. To investigate this, we used three experimental lines of zebrafish (Danio rerio) exposed to positive (large-harvested), negative (small-harvested) and random (control line) size-selective mortality for five generations. We tested prezygotic preferences through choice tests and spawning trials. In the preference tests without controlling for body size, we found that females of all lines preferred males of the generally larger small-harvested line. When the body size of stimulus fish was statistically controlled, this preference disappeared and a weak evidence of line-assortative preference emerged, but only among large-harvested line fish. In subsequent spawning trials, we did not find evidence for line-assortative reproductive allocation in any of the lines. Our study suggests that size-selection due to fisheries or natural predation does not result in reproductive isolation. Gene flow between wild-populations and populations adapted to size-selected mortality may happen during secondary contact which can speed up trait recovery.

In fisheries worldwide, larger fish are subjected to substantially greater fishing mortality than smaller fish. Body length and behavioral traits are often correlated, such that fisheries-induced changes in either behaviour or morphology can also alter other traits as result of direct or indirect selection. Consistent behavioral differences among individuals, known as personality traits, provide the proximate framework by which selection can act; however, empirical evidence regarding how size-selective harvesting alters mean personality traits in exploited stocks is scarce. We examined three experimental lines of zebrafish (Danio rerio) that were exposed to positive, negative or random size-selective harvest over five generations to investigate whether simulated fishing changed the mean personality of the survivors five generations after harvesting was halted. We found that females mean boldness (defined as risk-taking tendency), activity and sociability were significantly altered relative to a randomly harvested line; however, harvest-induced changes in personality were only detected in the negatively size-selected line, in which 75% of the smallest fishes were harvested. By contrast, we did not find evidence for harvest-induced evolution of personality in the positively size-selected line, in which 75% of the largest fishes were harvested. We conclude that size-selective harvesting alters individual fish personality in a social fish.