Buoyancy adjustment after swimbladder puncture in cod Gadus morhua: An experimental study on the effect of rapid decompression in capture-based aquaculture

Swimbladder puncture occurs frequently during fishing operations employed in capture-based aquaculture (CBA). The function, survival and welfare of cod Gadus morhua following controlled swimbladder puncture in the laboratory was investigated. Anaesthetised cod (n=30) were exposed to reduced pressure using a vacuum chamber and their swimbladders were punctured. The pressure reduction before puncture (similar to 70%), location of the swimbladder puncture sites near the pin bones, intraperitoneal gas evacuation path leading to the anal area and rapid repair mechanism, among other puncture characteristics, were consistent with previous findings. The mortality was low (similar to 6%) during the procedure and did not differ from that of the control group. The experimentally punctured cod were challenged by swimbladder reinflation in a flow-through pressure chamber supplied with a surveillance camera and remote pressure regulation. The punctured fish were capable of swimbladder inflation shortly after puncture and their buoyancy acclimation rates were similar to those of the control fish, with a mean filling rate of 0.22 m h(1). These experiments indicate that swimbladder puncture has minor short-lived and reversible effects on the welfare of the fish.