The effects of venting and decompression on Yellow Tang (Zebrasoma flavescens) in the ornamental aquarium fish trade

Each year, over 45 countries export 30 million fish from coral reefs as part of the global marine ornamental aquarium trade. This catch volume is affected by collection methods that cause mortality. Barotrauma caused by forced ascent of collected fish from depth has been determined to be a cause of post-collection mortality. The detrimental effects of barotrauma can be prevented by decompression, or mitigated with venting (puncturing the swim bladder to release expanded internal gas). To further evaluate the effects of collection methods on fish stress and mortality, we conducted the first comprehensive study on the effects of barotrauma prevention and mitigation practices on marine ornamental fish. We examined the effects of three ascent treatments, each with decompression stops of different frequency and duration coupled with or without venting, on sublethal effects and mortality in yellow tang (Zebrasoma flavescens), using histology and serum cortisol measurements. In Z. flavescens subjected to ascent without decompression stops or venting, a mean post-collection mortality of 6.2% occurred within 24h of capture. Common collection methods in the fishery, ascent without or with one decompression stop followed by venting, resulted in no mortality. Histopathologic examination of heart, liver, head kidney, and swim bladder tissues in fish 0d and 21d post-collection revealed no significant lesions in any treatment group. Ascent without decompression stops resulted in significantly higher serum cortisol than ascent with many decompression stops, and venting alone did not affect cortisol. Future work should examine links in the supply chain following collection to determine if further handling and transport stressors affect survivorship and sublethal effects.