Benjamin W Lindsey, Frank M. Smith, and Roger P. Croll

Teleost fish contain a variety of tissues, such as muscle, cartilage, and bone, which are denser than the external aqueous environment. Without compensatory mechanisms to provide buoyancy, fish would, therefore, sink. Consequently, the performance of essential behaviors such as feeding, predator avoidance, migrations, and reproduction¹ would be energetically costly as fish would need to swim constantly to maintain a vertical position in the water column. To overcome this problem, fish have evolved numerous mechanisms to achieve neutral buoyancy. These mechanisms include the development of watery muscle, synthesis of low-density lipids, and reduction in bone mass (reviewed in Refs.^1–3). However, of all buoyancy compensating mechanisms, a gasfilled organ in the coelomic cavity, the swimbladder, is considered to be the most efficient.² By controlling the volume of gas in the swimbladder, fish can attain neutral buoyancy at any depth, thereby minimizing the amount of energy expended by swimming to hold vertical station in the water column.

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Lindsey et al., 2010 (3.1 MB)