Development of the swimbladder as a buoyancy organ in the zebrafish.

摘要

Teleost fishes have body tissues that are denser than water, causing them to sink. To compensate for negative buoyancy, many teleosts possess a gas-filled swimbladder that provides lift, allowing these fish to attain neutral buoyancy at a specific depth. In this thesis I investigate three related problems in swimbladder-bearing fishes, using the zebrafish (Danio rerio) model: (1) the contribution of the swimbladder to animal buoyancy at different stages of larval development; (2) the behavioural response of adult zebrafish to simulated changes in depth; and (3) the effects of altered gravity on initial swimbladder inflation and development. Prior to initial swimbladder inflation zebrafish larvae were negatively buoyant and could not remain suspended in the water or execute vertical movements greater than a few centimeters. Thus, ascent towards the surface of the water for swimbladder inflation could only be achieved by larval attachment to the surrounding substrate. Following inflation, the volume of gas in the swimbladder allowed zebrafish to maintain near neutral buoyancy at all depths correlated with different stages of larval development. Adult zebrafish exposed to a simulated increase in depth of 50 cm or 100 cm H2O did not significantly increase their depth in the observation chamber over an 8 hour recording period. Zebrafish eggs and larvae exposed to short periods of simulated microgravity showed that once swimbladder inflation occurs, increases in volume and anatomical development of this organ follows a similar time course to the swimbladder of zebrafish raised under normal gravity. This work provides insight into the buoyancy contribution of the swimbladder during larval development and the importance of swimbladder inflation for the behaviour of fishes and for the use of zebrafish as a vertebrate model for gravitational biology.