Development of a hyperbaric trap-respirometer for the capture and maintenance of live deep-sea organisms

Abstract

A major obstacle to the investigation of deep-sea biology is the lack of instrumentation to retrieve deep-sea organisms from their habitat alive, particularly fishes with physoclistous swimbladders. To perform physiological experiments on deep-sea fishes under in situ but controlled conditions, we constructed a high-pressure fish trap-respirometer to capture deep-water fishes at depth and return them to the surface alive at in situ pressure and temperature. Pumps and instrumentation connected aboard ship or in the laboratory are used for maintenance of the animal and experimentation. The trap was designed so that respiration rates, pressure tolerance, and metabolic responses to various gas concentrations (CO 2 and O 2 ) could be examined in a controlled environment. The trap is deployed as an autonomous lander or free vehicle to depths of 4000 m. Once on the seafloor, a fish is captured on a baited hook that triggers the reeling of the fish into the pressure vessel and closure of its sealing door. Two fish, Coryphaenoides acrolepis, have been recovered live from 1450 m and maintained in the laboratory. Both fish were retrieved at ~95% of their in situ pressure and at temperatures of ~6°C. Oxygen consumption rates of these fish were 54.99 µmol O 2 kg ‐1 h ‐1 (1.158 kg, 65.0 cm total length, 23.5 cm pre-anal fin length) and 79.43 µmol O 2 kg ‐1 h ‐1 (1.305 kg, 66.5 cm total length, 24.5 cm pre-anal fin length). The latter fish was maintained for 3.5 d, and it survived gradual decompression to 76% of the pressure at its capture depth.