WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2024 25 after hatching, with daily growth deficits of > 40 percent occurring with increases in larval density of 2-4 times (Margulies et al. 2016, IATTC 2021). Experimental work has also shown that microscale turbulence has a strong influence on the feeding success and survival of YFT larvae (Kimura et al. 2004), and the optimum level of microturbulence found in laboratory trials, which is an intermediate level, corresponds to wind speeds of 2-5 m/sec which has been compared to historical wind speeds measured in the EPO (Margulies et al. 2016, Margulies et al. In Press). The wind speed-recruitment analysis is a potentially powerful tool in assessing YFT recruitment patterns in fisheries science. As part of the ELHG’s ecological studies, an important ongoing research project is the collaborative work between the ELHG and the Aquaculture Research Institute of Kindai University (KU) in Japan. These studies have included comparative investigations of the reproductive biology, genetics, and early life history of YFT and Pacific bluefin tuna (PBF). The project began in 2011, when the IATTC, KU, and the Autoridad de los Recursos Acuáticos de Panamá (ARAP) began a 5-year project funded by the Japan International Cooperation Agency (JICA) and the Japan Science and Technology Agency (JST). Since 2017, the project has continued using internal funding from IATTC and KU, and currently, the project has produced an extensive collection of unique experimental data comparing different aspects of the early life histories of both species. Most of the comparative experimental work is conducted at the Achotines Laboratory and the KU Aquaculture Research Institute, Oshima Station, in Wakayama Prefecture, Japan. Although PBF are temperate and subtropical, and YFT are tropical to subtropical in their adult life histories, both species require warm water ecosystems (>24° C) during their early life stages, enabling the possibility for comparative studies of early life history traits. Studies have been conducted comparing starvation resistance of first-feeding larvae, feeding habits, and effects of food type and density on growth and survival of larvae up to 2 weeks of life. Another successful outcome from this collaborative research was the world-first transfer in 2015 of laboratory-reared YFT juveniles at the Achotines Laboratory to a sea-cage located offshore of Achotines Bay (Figure 5), emphasizing the potential of this species for Aquaculture. Physiology and Biology Research Studies on biology and physiology of tunas are of fundamental importance, as they give scientific support for management of fisheries, and for the development of rearing protocols for aquaculture. Coupled with ecological studies, they are the core of the ELHG research. Temporal variation in growth of YFT was studied in the Panama Bight (Wexler et al. 2007) as well as age validation and growth of YFT larvae reared in the laboratory through validation of otolith increments (Wexler et al. 2001). The development of the visual system and inferred performance capabilities of larval and early juveniles was studied at Achotines Laboratory in species such as black skipjack, bullet and/ or frigate tunas, and sierra (Margulies 1997). Later, the developmental changes in the visual pigments of YFT were described (Loew et al. 2002). Even though larval tuna are relatively near-sighted and possess pure-cone retinas with no dark-light adaptive ability, visual acuities and eye morphology are somewhat advanced when compared with other marine fish larvae. During the juvenile transformation phase, YFT exhibit an increased sensitivity in low light, thus increasing the visual capability for foraging in deeper waters. Moreover, YFT first-feeding larvae show cone absorbances of pigments that are found in adults (with maximum sensitivity at 423 and 495 nm), but also a third green-sensitive pigment with maximum sensitivity greater than 560 nm, that disappears in the early juvenile stages of development but aids in detection and foraging on planktonic prey during the larval stage. These physiology studies have provided important findings that can be translated to adaptive rearing protocols for YFT and other tuna species (Figure 6). First-feeding larvae are reared under light conditions, since larvae cannot feed in the dark; green water seems to be an important component in rearing tanks, especially during the green-sensitive peaks occurring in the visual pigments in the larvae, maximizing visual contrast with zooplankton prey. YFT FIGURE 6. Experimental larval tanks of the Achotines Laboratory. Studies on biology and physiology of tunas are of fundamental importance, as they give scientific support for management of fisheries, and for the development of rearing protocols for aquaculture. Coupled with ecological studies, they are the core of the ELHG research. (CONTINUED ON PAGE 26)
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