42 DECEMBER 2022 • WORLD AQUACULTURE • WWW.WA S .ORG In the hours that followed, while the divers’ return was awaited, as divers need to carry out their long decompression process, the quality of the water for the fish was maintained by exchanging it for cooled surface seawater, removing nitrogenous compounds and maintaining the ideal physical and chemical conditions for captured fish. At this stage, temperature needs to be strictly controlled using ice in closed bags to keep parameters close to that found where fish were captured. For this, an electronic thermostat with DC power2 was used, with a probe submerged in the recirculation water, whose purpose is to facilitate temperature evaluation, allowing quick adoption of corrective measures. Upon returning to port, the chamber is sealed again at current working pressure and transported to a nearby base, where the set is reconnected to the pressure line. In this phase, the system is powered by AC energy and temperature is controlled using a wellsized chiller. The hyperbaric chamber built by Biomarine underwent certain modifications compared to the original model of the SubCAS (Shepherd 2018). First, a strength handle constructed with 15-mm HDPE using a CNCmilling machine was affixed to structural points with stainless steel screws. In the original project, this structure is composed of a PVC pipe spare with a register used to close the chamber, which is also used as a force lever that allows the application of the necessary torque to close and seal a lid next to the chamber’s body. The Biomarine team considered the implementation of a true force loop to be more convenient as it eliminates the risk of PVC breakage and also serves as protection and cover for the inlet and outlet registers of the hyperbaric chamber, which were also modified to be minimalistic. Two simple quick-connect valves were adopted to thread on the ¼” type inlet and 3/8” type outlet connections of the hyperbaric chambers. These registers have their opening/closing handle shortened to prevent them from being accidentally opened during ascent. In addition, a conventional 3/8” pressure control valve for filtering systems was installed in the pressure line. It was a simple, low-cost and functional solution, because the valve originally used in the original design of the SubCAS3 is not easily found in the Brazilian market. The hyperbaric system generates a back pressure that prevents fish from being brought to the surface in the final phase of the decompression process. This situation was reported in the original SubCAS project (Shepherd 2018) and was also verified in the Biomarine project. To overcome this problem, three levels of bypasses were installed in the pressure line (before the chamber Location of dives on the coast of Bahia, Brazil. Fish capture was designed to be carried out with hand nets. In addition, divers were instructed to collect predetermined species that were selected for captive breeding studies: eyestripe bass Liopropoma aberrans, French butterflyfish Prognathodes guyanensis and roughtongue bass Pronotogrammus martinicensis, all available at the planned depth. Species were chosen based on images from previous mesophotic dives made at the site. To enable decompression of the collected fishes, the SubCAS technique (Shepherd 2018) was adopted with some modifications. It consists of a portable, submersible hyperbaric chamber that is taken to depth by divers. Captured fish are kept in the chamber under pressure to avoid occurrence of hyperbaric issues, allowing decompression process to occur at the surface in a slow and controlled way, avoiding rapid changes that can cause barotraumas and sometimes death. The SubCAS technique keeps pressure stable inside the hyperbaric chamber during the course of ascending following completion of a dive with the aid of a small air bubble injected before the chamber’s complete closing. This air bubble expands as divers head to the surface, compensating for the reduction in external pressure and compliance of the polycarbonate chamber body, thus preventing significant internal pressure variations (Boyle-Mariotte Law). For fish, the pressure does not change significantly even when the chamber is already at the surface. The chamber closure was planned to occur between 60 and 70 m to prevent fish from being exposed to excessive decompression from the collection point (Shepherd 2018). Two methods were tested to assure chamber recovery: the first consisted of a manual search by the support teamwhen the deep-sea divers reached 30 m depth, within one hour after the beginning of the dive, following the SubCAS standard operating method. The second method consisted of finding the divers with a small ROV (remotely operated underwater vehicle) at 70 m deep, 30 min after the start of the dive; then, the surface team quickly pulls the equipment and camera fixed to the diver’s robotic arm. This second method was designed with an additional mechanism to reduce the chamber’s exposure to high temperature at the water surface. After being received at the surface, the chamber was connected to a high-pressure system that promotes saltwater recirculation, keeping water oxygenation for the captured specimens. Pressure is maintained using a high-pressure water pump1 powered by two 55-A stationary batteries. The internal pressure was determined by operating a pressure relief valve.
RkJQdWJsaXNoZXIy MjExNDY=