Physiological effects of swim bladder overexpansion and catastrophic decompression on red snapper

The commercial and recreational harvests of red snapper Lutjanus campechanus in the Gulf of Mexico have declined over the past five decades, prompting strict regulations. Release mortality associated with catastrophic decompression (CD) is a possible cause for the continuing decline, although to date no physiological data exist to support this assumption. Using a flowthrough high-pressure chamber, subadult red snapper were acclimated to 101.2, 405.3, 608.0, and 1,215.9 kPa, simulating depths typical of their distribution (as deep as 200 m), and then decompressed at a rate of 10.1 kPa/s. Lateral and dorsal X-ray imaging in combination with necropsy showed that swim bladders expanded in a predictable manner. Ventral expansion into the caudal body cavity space occurred at lower pressures, whereas expansion into the cranial portion of the body cavity occurred at the highest pressure. Expansion patterns resulted in over 70 different overexpansion injuries, the most severe being to vital organs. Our results suggest a specific suite of clearly identifiable injuries associated with CD that increase in number and severity as retrieval depth increases. A more thorough understanding of catastrophic decompression syndrome will provide insight into the declining fishery and aid in developing effective physiology-based management strategies.