Video-based quantification of escape behaviors in individual and groups of fish exposed to a simulated visual predator

J.D. Salierno¹ and A.S. Kane^1,2

¹Aquatic Pathobiology Laboratory, Department of Veterinary Medicine, University of Maryland, College Park, MD, USA
²Virgina-Maryland Regional College of Veterinary Medicine, College Park, MD, USA

The ability of fish to actively avoid and evade predation is essential to the success of the individual. In order to accomplish these feats, fish must maintain a functional suite of behaviors to cope with predation pressure. Further, these behaviors must be adaptive in order to accurately respond to fluctuations in predation pressure. We examined predator response behaviors of individual and groups of killifish, Fundulus heteroclitus, to a simulated visual aerial predator, to investigate if response behaviors remain similar after repeated simulated ‘threats’, and if responses vary based on whether they are alone or in a group. The killifish is a good model for the investigation of predator avoidance behaviors because they live in shallow estuarine habitats and are vulnerable to aerial predation threats. We used a computer-based video tracking system (Videoscript Professional©, v. 3.1) to record 15 seconds of baseline movement before, and 15 seconds of movement after, presentation of the visual ‘fly-by’ stimulus. The stimulus consisted of wood bird silhouettes that ‘flew’ over the exposure arenas. The visual ‘fly-by’ stimulus elicited a signi.cant response whereby 96% of the individual fish and 95% of the groups of .sh exhibited a startle response followed by cessation of movement. This cessation of movement lasted for 12.4 (±0.9) seconds for individual fish and 8.2 (±0.3) seconds for groups of fish, which were significantly different. Velocity and percent movement for groups of fish, before and after the simulated predator presentation, were consistently higher than what was observed for individuals. Groups of fish responded with significant decreases in average velocity, shoal velocity, interactions, movement and shoaling activity, along with significant increases in aggregation (no movement component). Groups of fish displayed a higher degree of overall movement and initiated swimming behaviors compared with individuals, thus punctuating the ability for killifish to alter predator response behaviors based on social dynamics. As a result, these eminently repeatable and quantifiable responses could serve as endpoints for the investigation of alterations in predator avoidance behaviors in association with stress or toxicant exposure.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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