Effects of group size and landmarks on escape behavior of three fish species

Utilizing shelters and living in groups are key anti-predator strategies among fish. Species that have evolved under different ecological conditions may exhibit distinct escape behaviors, reflecting variations in cognitive ability and social information transfer. This study investigate3-fishesd how group size and visual landmarks shape collective escape behavior in fish species from divergent flow habitats: the demasoni cichlid (Chindongo demasoni, preferring stagnant water), zebrafish (Danio rerio, preferring slow-flowing water), and qingbo (Spinibarbus sinensis, preferring fast-flowing water). For each species, 1080 individuals were tested in a between-subjects design, distributed into groups of 3 or 6 with or without landmarks. Using a Y-maze, we assessed the effects of shoal size (3 vs. 6) and the presence of visual landmarks on escape accuracy and latency to enter a shelter arm following brief environmental exploration and a simulated predation stimulus. Results indicated that distinct anti-predator strategies were shaped by species-specific cognitive profiles. The demasoni cichlid exhibited the most cognitively flexible behavior, including rapid decision making and a landmark-dependent shift from passive sheltering to active patrolling. In contrast, zebrafish responded with a generalized increase in shelter use, whereas qingbo behavior was strongly mediated by group competition. The benefits of larger group size and landmark presence were context-dependent, challenging the universal applicability of collective intelligence theory. Our findings demonstrate that anti-predator decision making is deeply rooted in species' evolutionary histories, providing crucial insights for developing conservation strategies that account for behavioral adaptation and cognitive ecology.