A Simple System for Examining Buoyancy Regulation of Fish: A Case Study Illustrating the Vulnerability of Mekong River Fish to Barotrauma

Fish passing downstream through water regulating structures such as dams and weirs can be damaged by changes in water pressure termed barotrauma. Barotrauma in some species appears to be largely due to expansion and rupture of the swim bladder, which may vary greatly with the way they regulate buoyancy. Fish with closed swim bladders (physoclists) may be more susceptible to barotrauma than fish with open swim bladders (physostomes). However, little is known about how species regulate their buoyancy in the Lower Mekong Basin and how they are affected by changes in pressure associated with downstream passage at water regulating structures. Complex systems are available that can expose fish to pressures changes and allow buoyancy regulation to be examined but, these systems can be expensive. This is unfortunate since many of the poorly studied species that may be susceptible to barotrauma reside in countries with limited research facilities. However, much can be learned about the physiology of buoyancy using a simple inexpensive system that we describe. This system can be used to determine how vulnerable fish species are to injury or mortality during downstream passage which can then be used to help design fish-friend turbines, water gates and bypass systems.