The effect of respiratory mode and oxygen concentration on the risk of aerial predation in fishes

Abstract

Six bimodal and six water-breathing species of fish were exposed to predation by a green heron (Butorides striatus) in a laboratory experiment to examine the hypothesis that aerial predation selects against the evolution and use of air breathing. Tests were performed at 1.6 and 0.5 mg O 2∙L−1 ([Formula: see text] and 9 Torr, respectively; 1 Torr = 133.322 Pa). Most water breathers avoided the surface at 1.6 mg∙L−1 but not at 0.5 mg∙L−1, where they performed aquatic surface respiration. Most bimodal species breathed air at both oxygen concentrations. The risk of capture increased with proximity to the surface. The prey species responded to the predator by increasing mean depth, decreasing the rate of air breathing or aquatic surface respiration, and avoiding the vicinity of the predator when surfacing. Despite these and other antipredator characteristics, all species were vulnerable to capture in the test situation. Overall, the survivorship of water-breathing fishes was significantly higher than that of bimodal species at 1.6 mg∙L−1 and similar to that of bimodal species at 0.5 mg∙L−1. Aerial predation pressure should favor water breathing over air breathing except at oxygen concentrations lower than 0.5 mg∙L−1.