A context analysis of bobbing and fin‐flicking in a small marine benthic fish

Most antipredator strategies increase survival of individuals by signaling to predators, by reducing the chances of being recognized as prey, or by bewildering a predator's perception. In fish, bobbing and fin‐flicking are commonly considered as pursuit‐deterrent behaviors that signal a predator that it has been detected and thus lost its surprise‐attack advantage. Yet, very few studies assessed whether such behavioral traits are restricted to the visual presence of a predator. In this study, we used the yellow black‐headed triplefin Tripterygion delaisi to investigate the association between these behaviors and the visual exposure to (a) a black scorpionfish predator ( Scorpaena porcus ), (b) a stone of a size similar to that of S. porcus , (c) a conspecific, and (d) a harmless heterospecific combtooth blenny ( Parablennius sanguinolentus ). We used a laboratory‐controlled experiment with freshly caught fish designed to test for differences in visual cues only. Distance kept by the focal fish to each stimulus and frequency of bobbing and fin‐flicking were recorded. Triplefins kept greater distance from the stimulus compartment when a scorpionfish predator was visible. Bobbing was more frequent in the visual presence of a scorpionfish, but also shown toward the other stimuli. However, fin flicks were equally abundant across all stimuli. Both behaviors decreased in frequency over time suggesting that triplefin become gradually comfortable in a nonchanging new environment. We discuss why bobbing and fin‐flicking are not exclusive pursuit‐deterrent behaviors in this species, and propose additional nonexclusive functions such as enhancing depth perception by parallax motion (bobbing) or signaling vigilance (fin‐flicking).