Data from: Hypoxia increases the risk of egg predation in a nest-guarding fish

For fish with parental care, a nest should meet both the oxygenation needs of the eggs and help protect them against predators. While a small nest opening facilitates the latter, it impedes the former and vice versa. We investigated how the presence of potential egg predators in the form of shore crabs Carcinus maenas affects nest building, egg fanning, defensive displays and filial cannibalism of egg-guarding male sand gobies Pomatoschistus minutus under two levels of dissolved oxygen. In the high oxygen treatment, males retained their nest opening size in the presence of crabs, while males in low oxygen built large nest openings both in the absence and presence of crabs, despite the fact that crabs were more likely to successfully intrude into nests with large entrances. Males in low oxygen also fanned more. In the presence of crabs males increased their defensive displays, but while males in high oxygen reduced fanning, males in low oxygen did not. Filial cannibalism was unaffected by treatment. Sand gobies thus prioritize egg ventilation over the protection afforded by small nest openings under hypoxia and adopt defensive behaviour to avert predator attention, even though this does not fully offset the threat from the egg predators.对于存在亲本抚育行为的鱼类，其巢穴需同时满足鱼卵的供氧需求，并协助抵御捕食者。较小的巢穴开口虽有助于抵御捕食，却会阻碍鱼卵的供氧，反之亦然。本研究调查了在两种溶解氧水平下，以滨蟹（Carcinus maenas）作为潜在卵捕食者时，对护卵雄性沙𫚥虎鱼（Pomatoschistus minutus）的巢穴建造、扇卵行为、防御展示以及父本食卵行为的影响。结果显示：高氧处理组的雄鱼在滨蟹存在时，仍维持原有巢穴开口大小；而低氧处理组的雄鱼，无论滨蟹是否存在，均会建造更大的巢穴开口——尽管滨蟹更易侵入开口较大的巢穴。低氧处理组的雄鱼扇卵行为也更为频繁。当滨蟹存在时，雄鱼会增加防御展示行为；但高氧组雄鱼会减少扇卵频率，低氧组雄鱼则无此变化。父本食卵行为不受实验处理的影响。综上，在缺氧环境下，沙𫚥虎鱼会将卵的通风供氧置于小型巢穴开口所提供的防御保护之上，并通过防御行为规避捕食者的关注，尽管这无法完全抵消卵捕食者带来的威胁。