AB 3:291-296 (2008)  -  DOI: https://doi.org/10.3354/ab00088

Physical model of the development of external signs of barotrauma in Pacific rockfish

Robert W. Hannah1,*, Polly S. Rankin1, Alexandra N. Penny2, Steven J. Parker3

1Oregon Department of Fish and Wildlife, Hatfield Marine Science Center, 2040 SE Marine Science Drive, Newport, Oregon 97365, USA
2Brown University, Providence, Rhode Island 02912, USA
3National Institute of Water and Atmospheric Research, Private Bag 14901, Wellington, New Zealand

ABSTRACT: Four species of Sebastes (Pacific rockfish) showed evidence of a wide array of internal injuries from capture-induced barotrauma, including liver and swimbladder damage, organ displacement related to esophageal eversion, and hemorrhage in the pericardium and abdominal cavity. However, clear evidence of swimbladder rupture was not observed in all fish with external signs of barotrauma. Injection of air through the body wall into the swimbladders of rockfish carcasses generated all of the common external signs of barotrauma documented in wild-captured fish, suggesting that the physical effects of swimbladder gas expansion can create these gross external signs without embolism from dissolved blood gases. Dissections of injected black rockfish S. melanops carcasses showed that, typically, injected air escaped the swimbladder without obvious rupture, moving in an anterio-dorsal direction, generating bulges and air bubbles that were externally visible through the branchiostegal membrane. Injected air also collected dorsally to the esophagus, posterior to the pharyngeal teeth, causing the esophagus to roll outwards into the buccal cavity (esophageal eversion). Injected air also frequently traveled further forward, collecting medially to the eyeball, leading to exophthalmia, and then moved distally along the fascia, invading the corneal stroma from the edges, resulting in corneal emphysemas. Air injected into the swimbladders of quillback rockfish S. maliger carcasses generated similar eye effects, but also escaped through ruptures in the branchiostegal membrane and did not generate esophageal eversion, which is also infrequent in wild-caught specimens. These results demonstrate that the major external signs of barotrauma in Pacific rockfish can develop as result of escaping swimbladder gases following an internal  ‘path of least resistance’.

KEY WORDS: Discard mortality · Sebastes · Swimbladder · Decompression · Exophthalmia

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Cite this article as: Hannah RW, Rankin PS, Penny AN, Parker SJ (2008) Physical model of the development of external signs of barotrauma in Pacific rockfish. Aquat Biol 3:291-296. https://doi.org/10.3354/ab00088

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