Meeting Abstract

P3.61  Jan. 6  Development of buoyancy control in the zebrafish (Danio rerio) swimbladder LINDSEY, B.W.*; ROBERTSON, G.N.; MCGEE, C.A.S.; DUMBARTON, T.C.; CROLL, R.P.; SMITH, F.M.; Dalhousie University, Halifax, NS blindsey@dal.ca

The development of buoyancy control is critical to the survival and behavior of teleost fishes, yet the specific contribution of the swimbladder to maintaining vertical position in the water column in larval and adult forms is unknown. Here we use the zebrafish (Danio rerio) to investigate the correlation between the anatomical development and innervation of the swimbladder and the capability to control buoyancy. Inflation of the initially single-chambered swimbladder occurred at 4-5 days post hatching at which time larvae (≤ 4 mm body length) rose to the surface and remained within the top 1-3 cm of the observation tank with minimal swimming activity. A rete of parallel arteries and veins was present in the swimbladder as well as paired lateral nerves; however no discernable smooth muscle was observed. Following evagination of the second chamber (≥ 6 mm) the anterior and posterior chambers were joined by a wide ductus communicans. The innervation of the rete became more extensive and a band of nascent smooth muscle cells emerged along the sides of the posterior chamber. From this early double-chambered stage onward fish swam to a maximum depth of 36 cm and as juveniles (≥ 8-9 mm) showed coordinated swimming activity similar to adults. By this stage, the ductus communicans had narrowed and a band of organized smooth muscle formed in the lateral wall of the posterior chamber, as well as the development of innervation. Adults (≥ 15-20 mm) displayed a preferred depth 10-16 cm below the surface. Our data suggest that buoyancy control via the swimbladder in the zebrafish may occur only after the transition to a double-chambered organ, and relies on the presence and innervation of functional musculature on the posterior chamber for reflexive inflation and deflation.