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

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'.

The Differential Response to Decompression in Three Species of Nearshore Pacific Rockfish

“…Panel (C) shows a lower-magnification (253) view of the tissue section; note that the gas bubbles are located near the periphery. DECOMPRESSION RESPONSE IN PACIFIC ROCKFISH yellowtail rockfish are able to release excess gas in their swim bladder by way of their pharyngo-cleithral membrane, the trapped gas likely does not build up enough pressure to cause external indicators of barotrauma (such as everted esophagus and exophthalmia; Hannah et al 2008a). Hannah et al (2008a) showed that eversion of the esophagus and exophthalmia in rockfish is caused by gas escaping from an unruptured or ruptured swim bladder into the body cavity and moving in an anteriodorsal direction.…”

Release mortality in the red snapper (Lutjanus campechanus) fishery: a meta-analysis of 3 decades of research

“…3-6). Presence of a positive correlation between depth and mortality is frequently reported in the literature, and the relationship is thought to be associated primarily with injuries sustained during decompression, such as overexpansion and rupture of the gas bladder, esophageal eversion, cloacal prolapse, exophthalmia, and gas infusion into vital organs (Davis, 2002;Rummer and Bennett, 2005;Hannah et al, 2008). The development of a predictive relationship with depth is important because previous stock assessments of red snapper, completed before this model, were based on single estimates that were fixed by region (i.e., east and west GOM) rather than on a depth relationship.…”

Modeling submergence success of discarded yelloweye rockfish (Sebastes ruberrimus) and quillback rockfish (Sebastes maliger): Towards improved estimation of total fishery removals

“…Similar to the findings of Hannah et al (2008a), the barotrauma signs that are associated with maximal retention of excess gases were identified as being highly important for both yelloweye and quillback but these signs differed between the two species. External signs of barotrauma develop as excess gases travel in a dorsal-anterior direction along the path of least resistance and when in sufficient quantities, invade other body cavities such as ocular orbits and/or force esophageal tissue and the stomach into the buccal cavity (Hannah et al, 2008b). When barotrauma signs associated with maximal gas retention were present, the probability of failure to submerge exceeded the probability of successful submergence for both species.…”