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. Whilst 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 prioritise 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.

对于存在亲代抚育行为的鱼类而言，鱼巢需同时满足鱼卵的供氧需求，并为其提供抵御捕食者的保护。狭小的巢穴开口虽有助于提升防御效果，却会阻碍供氧；反之亦然。本研究以滨蟹（Carcinus maenas）作为潜在鱼卵捕食者，设置两种溶解氧水平，探究其对守护鱼卵的雄性沙鳚（Pomatoschistus minutus）的筑巢、扇卵、防御展示及亲代食卵行为的影响。在高溶解氧实验组中，雄鱼在有滨蟹存在时维持其巢穴开口的原有尺寸；而低溶解氧实验组的雄鱼，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鱼巢。低溶解氧组的雄鱼扇卵频率也更高。当滨蟹存在时，雄鱼会提升防御展示行为；但高溶解氧组的雄鱼会降低扇卵频率，低溶解氧组则无此变化。亲代食卵行为不受实验处理的影响。由此可见，在低氧环境下，雄性沙鳚会优先保障鱼卵的通气供氧需求，而非依赖狭小巢穴开口提供的防御保护；它们会采取防御行为以规避捕食者的关注，尽管此类行为无法完全抵消鱼卵捕食者带来的威胁。