Buoyancy regulation and barotrauma in two species of nearshore rockfish

Fishes with closed swim bladders regulate buoyancy during depth changes by secreting and resorbing swim bladder gases. Forced ascent during fishery capture results in barotrauma caused by rapid expansion and exsolution of gases from body fluids. Pressure changes in hyperbaric chambers were used to examine changes in swim bladder integrity and acclimation rates in two ecologically different, yet congeneric, species: black rockfish Sebastes melanops and China rockfish S. nebulosus. We also conducted simulated-capture experiments to investigate the relationship between capture in a fishery, barotrauma from pressure change, and survival after release. Black rockfish acclimated faster than China rockfish to both increases and decreases in pressure, but both species were much slower to acclimate than other physoclists, such as Atlantic cod Gadus morhua. Black rockfish required up to 48 h to acclimate from 4 atmospheres absolute (ATA; depth equivalent of 30 in) to surface pressure and required up to 168 h to become neutrally buoyant at 4 ATA after starting from surface pressure. In contrast, China rockfish required over 250 h to become neutrally buoyant at 4 ATA after starting from surface pressure. All black rockfish exposed to a 3-ATA decrease in pressure during simulated capture had ruptured swim bladders. However, mortality from simulated capture and subsequent recompression was low; only 3.3 +/- 1.7% (mean +/- SE) mortality was observed after 21 d. In experiments with black rockfish, rapid recompression reversed visible barotrauma, suggesting that a quick return to depth could be used to minimize mortality of discarded black rockfish in nearshore fisheries.