The contribution of the swimbladder to buoyancy in the adult zebrafish (Danio rerio): A morphometric analysis

• DOI: 10.1002/jmor.10610
• Publication Date: 2008-02-26T23:16:45Z
• Authors: George N. Robertson; Benjamin W. Lindsey; Tristan C. Dumbarton; Roger P. Croll; Frank M. Smith
• Keywords: Male; 0301 basic medicine; 03 medical and health sciences; Air Sacs; Pressure; Animals; Body Weights and Measures; Female; 14. Life underwater; Swimming; Zebrafish

AbstractMany teleost fishes use a swimbladder, a gas‐filled organ in the coelomic cavity, to reduce body density toward neutral buoyancy, thus minimizing the locomotory cost of maintaining a constant depth in the water column. However, for most swimbladder‐bearing teleosts, the contribution of this organ to the attainment of neutral buoyancy has not been quantified. Here, we examined the quantitative contribution of the swimbladder to buoyancy and three‐dimensional stability in a small cyprinid, the zebrafish (Danio rerio). In aquaria during daylight hours, adult animals were observed at mean depths from 10.1 ± 6.0 to 14.2 ± 5.6 cm below the surface. Fish mass and whole‐body volume were linearly correlated (r2 = 0.96) over a wide range of body size (0.16–0.73 g); mean whole‐body density was 1.01 ± 0.09 g cm−3. Stereological estimations of swimbladder volume from linear dimensions of lateral X‐ray images and direct measurements of gas volumes recovered by puncture from the same swimbladders showed that results from these two methods were highly correlated (r2 = 0.85). The geometric regularity of the swimbladder thus permitted its volume to be accurately estimated from a single lateral image. Mean body density in the absence of the swimbladder was 1.05 ± 0.04 g cm−3. The swimbladder occupied 5.1 ± 1.4% of total body volume, thus reducing whole‐body density significantly. The location of the centers of mass and buoyancy along rostro‐caudal and dorso‐ventral axes overlapped near the ductus communicans, a constriction between the anterior and posterior swimbladder chambers. Our work demonstrates that the swimbladder of the adult zebrafish contributes significantly to buoyancy and attitude stability. Furthermore, we describe and verify a stereological method for estimating swimbladder volume that will aid future studies of the functions of this organ. J Morphol., 2008. © 2008 Wiley‐Liss, Inc.