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

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Abstract
Bimodal (6) and 6 water-breathing species of fish [Trichogaster trichoptera, Helostoma temmincki, Macropodus opercularis, Hypostomus sp., Pangasius sp., Umbra limi, Cichlasoma biocellatum, Jordanella floridae, Xiphophorus helleri, Hemigrammus caudovittatus, Brachydanio rerio and Lepomis gibbosus] 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 O2 .cntdot. l-1 (pO2= 30 and 9 Torr, respectively; 1 Torr = 133.322 Pa). Most water breathers avoided the surface at 1.6 mg .cntdot. l-1 but not at 0.5 mg/l-1, where they performed aquatic surface respiration. Most bimodal species breathed air at both O2 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. The survivorship of water-breathing fishes was significantly higher than that of bimodal species at 1.6 mg .cntdot. l-1 and similar to that of bimodal species at 0.5 mg .cntdot. l-1. Aerial predation pressure should favor water breathing over air breathing except at O2 concentrations lower than 0.5 mg .cntdot. l-1.