A Macroscopic to Microscopic Study of the Effects of Barotrauma and the Potential for Long-term Survival in Pacific Rockfish

approved: _____________________________________________________________________ Carl. B. Schreck Steven J. Parker Depleted species of rockfish (Sebastes spp.) from the Northeast Pacific experience high discard mortality due to “barotrauma,” induced from the rapid change in pressure during capture. Research suggests rockfish have the potential to survive barotrauma if immediately recompressed, but the potential for long-term recovery is unknown. In this project, we studied the injuries that occur in rockfish during barotrauma and the potential for rockfish to recover from these injuries using a macroscopic to microscopic to molecular approach. We first assessed multiple species of rockfish for macroscopic and tissue-level injuries as a result of barotrauma; these injuries tended to be species-specific and included ruptured swimbladders, emphysema in the heart ventricle, emboli in the rete mirabile, and emboli in the head kidney. Next we investigated the potential for longerterm recovery in black rockfish (S. melanops) that underwent simulated decompression from 4.5 ATA (35 m depth) and subsequent recompression using hyperbaric pressure chambers. We assessed recovery over a 31 day period at three different time points at the macroscopic level, tissue level, blood level, and molecular level. Macroscopic and tissue level injuries included ruptured swimbladders, which were slow to heal in some fish, and injury to the rete mirabile. At the blood level, we found no differences between treatment and control fish. At the molecular level, we created a rockfish-specific cDNA microarray to search for genes that might be differentially regulated as a result of barotrauma. We identified six genes from the innate immune system that were up-regulated at day 3 in treatment fish but were no longer up-regulated at day 31. In conclusion, recompressed rockfish will not be as competent as uncaptured rockfish because of unhealed swimbladders, injury to the rete mirabile, and up-regulation of the innate immune system. However, even rockfish that are injured will have a chance at survival that they would not have if they were not recompressed. The resumption of feeding, the ability of most swimbladders to hold gas again, the lack of a difference in blood chemistry measures between treatment and control fish, and the return of immune genes to neutral regulation are all good indicators that many black rockfish do have the potential for recovery. ©Copyright by Alena L. Pribyl February 9, 2010 All Rights Reserved A Macroscopic to Microscopic Study of the Effects of Barotrauma and the Potential for Long-term Survival in Pacific Rockfish