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而言，其筑造的巢穴需同时满足鱼卵的供氧需求，并协助抵御捕食者的侵袭。缩小巢穴开口虽能强化防护效果，却会阻碍供氧过程，反之亦然。我们在两种溶解氧水平条件下，探究了以滨蟹（Carcinus maenas）为代表的潜在卵捕食者，对护卵雄性小沙虾虎鱼（Pomatoschistus minutus）的筑巢行为、卵扇动行为、防御展示行为以及食卵行为的影响。在高氧处理组中，雄鱼在有滨蟹存在的情况下仍维持原有巢穴开口尺寸；而低氧处理组的雄鱼，无论是否存在滨蟹，均会营建更大的巢穴开口——尽管滨蟹更易侵入开口较大的巢穴。低氧处理组的雄鱼同时会提升卵扇动频率。当滨蟹存在时，雄鱼会增强防御展示行为；但高氧组雄鱼会降低卵扇动频率，低氧组雄鱼则无此变化。食卵行为不受实验处理的影响。综上，小沙虾虎鱼在低氧环境下，会将卵的通气需求置于通过缩小巢穴开口获得的防护优先级之上，并通过调整防御行为规避捕食者的关注，尽管此举无法完全抵消卵捕食者带来的威胁。