WWW.WA S .ORG • WORLD AQUACULTURE • DECEMBER 2022 41 Detail of the hyperbaric chamber used by Biomarine. basic manual equipment. On the other hand, it is a high-cost apparatus, requiring a backup system, rigorous training and careful maintenance (Mocsári 2015). Diving with helium-based gas mixtures, especially trimix (a mixture of oxygen, nitrogen and helium), has allowed this equipment to be used for diving in the mesophotic range. By defining an appropriate plan and the correct proportion of gases, the diver can control hyperoxia and the narcotic level of the mixture (Mocsári 2015). Considering these challenges and opportunities, Biomarine has been working towards assimilation and technological development in the mesophotic marine fish area, with the purpose of collecting specimens for the development of reproductive protocols, resulting in the expansion of knowledge about these species. Development of capture techniques can allowmesophotic specimens to be available at different larval stages for ichthyological studies, also enabling the supply of young fish for scientific purposes. Economically, the reproduction of mesophotic species shows great potential. In fact, mesophotic fish are rare in the aquarium market and, when available, reach high economic values. For example, specimens of French butterflyfish Prognathodes guyanensis from the Caribbean Sea, reach a retail value of US$2,500 in the North American market. Based on this challenge and opportunity, the Biomarine team planned and executed two mesophotic diving operations in Bahia, Brazil, aiming to evaluate the operational conditions of fish capture at depths below 100 m. Indeed, the collection of fish frommesophotic depths and to safely bring them to surface is a great challenge. Hence, operations were planned one year in advance. The time was used for construction and acquisition of equipment, methodological planning, system experimentation and adjustments. Divers László Mocsári and Peter Tofte accepted the invitation to participate, operating as deepsea divers. Both are highly experienced technical divers accustomed to extreme rebreather diving and were responsible for each dive’s individual planning, including decompression stops, ‘bail out’ systems and gas mixtures. ( C O N T I N U E D O N P A G E 4 2 ) collection pressures, which also justifies making the effort on captive reproduction. In contrast, mesophotic species are rarely marketed, and when available, are very expensive. Thus, live individuals frommesophotic regions are not aways accessible for scientific experiments on reproduction in captivity. Although it is not possible to state mesophotic fishes are affected by the ornamental fish trade, it cannot be presumed that biodiversity of those ecosystems are totally preserved. Recent studies indicate signs of degradation in mesophotic coral reef ecosystems, highlighting the urgent need for governments to take action to protect those environments (Rocha 2018). Climate change, habitat competition with invasive species, professional, sport or ghost fishing, pollution, ocean acidification, mining activities, oil extraction and even naval accidents are some of the factors that impact mesophotic fauna. Mesophotic regions were still largely unknown (Pinheiro 2016), as they were located at a depth where scuba diving was not operationally viable and tended to be neglected even when manned submersibles were used. Considering the high operational cost of this equipment, its use tended to focus on greater depths, normally below 150 m, justifying the investment (Pyle 1996). As a result, the mesophotic depth range remained poorly known, although holding many species not yet described (Pyle 2000, Pinheiro 2016). As Richard L. Pyle indicated in his 1996 article, “Exploring deep coral reefs: howmuch biodiversity are we losing?,” the “Twilight Zone” or mesophotic regions have received little attention from researchers despite the available technology for exploration of abyssal and spatial zones. Pyle’s pioneering vision in the 1990s stimulated the scientific community to apply closed-circuit rebreather technology as a diving tool to assess mesophotic zones in subsequent years. Currently a large number of researchers are using this technical equipment to conduct studies in these areas. Using a rebreather allows divers to submerge for long periods. It is also silent and produces no bubbles, which makes it easier to approach live organisms, allowing the collection of specimens with Detail of the control valve of the hyperbaric chamber used by Biomarine. ROV used by Biomarine (Qysea Fifish V6S, 200m cable).
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