Egg Size Variation Between Wild and Captive Broodstock Brown Trout ( Salmo trutta ) in Watersheds of Three Peri‐Alpine Lakes

Captive environments could lead to plastic and/or heritable shifts in key life‐history traits, such as egg size. Although many studies have examined how egg size differs between wild and captive females, the results are mixed. Therefore, system‐specific studies on egg size variation are valuable. In the present study, we examined how wild‐caught and captive broodstock brown trout ( Salmo trutta ) differ in egg size using eggs from three peri‐Alpine lakes (Lake Constance, Lake Lucerne and Lake Zurich). In addition to clutch‐mean egg size, which has been extensively studied traditionally, we also focused on the degree of within‐clutch variation. There was no significant difference in the degree of within‐clutch variation between wild‐caught and captive broodstock females across the lake watersheds. However, variation in clutch‐mean egg size between wild‐caught and captive broodstock females differed among the lake watersheds. Specifically, captive broodstock females produced eggs slightly smaller than those of wild‐caught females in Lakes Lucerne and Zurich. In contrast, wild‐caught and captive broodstock females produced eggs of similar size in Lake Constance. Future studies elucidating the mechanisms underlying variation in egg size between wild‐caught and captive broodstock females and across lake watersheds are essential for a better understanding of the consequences of stocking programmes for wild brown trout populations in the watersheds of peri‐Alpine lakes.