The effect of swimming depth on respiratory behavior of the honey gourami, Colisa chuna (Pisces, Belontiidae)

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Abstract
We tested the hypothesis that fish capable of bimodal respiration would respond to the increased travel costs of surfacing by decreasing their frequency of air breathing. Honey gouramis were permitted to move freely in a 220 cm deep aquarium, but their preferred depths were manipulated by changing the location of shelter and feeding sites. With increased depth the interval between air breaths increased. This supports the argument that travel to and from the surface is a significant cost for air-breathing fish. It provides evidence that respiratory behavior can be affected by factors not directly involved in the physiology of gas exchange. Furthermore, it suggests that retention of water-breathing capacity in air-breathing species may reduce the costs of breathing through adaptive changes in partitioning.