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Aquatic Biology

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AB 25:97-106 (2016)  -  DOI:

Micro CTD data logger reveals short-term excursions of Japanese sea bass from seawater to freshwater

Naoyuki Miyata1,*, Tomohiko Mori1, Masaaki Kagehira2, Nobuyuki Miyazaki3, Michihiko Suzuki4, Katsufumi Sato1

1Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8564, Japan
2Oita Prefecture Southern Region Bureau Rural Community Promotion Department, Saiki, Oita, 876-0813, Japan
3Japan Marine Science Foundation, Taito, Tokyo, 110-0008, Japan
4Little Leonardo, Bunkyo, Tokyo, 113-0021, Japan
*Corresponding author:

ABSTRACT: We conducted calibration tests and field deployments of a newly developed micro CTD data logger on Japanese sea bass Lateolabrax japonicus to measure fine-scale movement and reconstruct micro-salinity profiles of estuarine habitat. In June, July and November 2013 and 2014, Japanese sea bass were caught in the Ohno (33°12’N, 131°36’E) and Oita (33°16’N, 131°41’E) Rivers in Oita Prefecture, Japan. In seawater tanks, the measurement drift for salinity was negligible over a 2 wk period (n = 8). Moreover, in the estuary, the values of standard seawater measured at pre- and post-deployment of sensors on fish were consistent to the first decimal place; therefore, sensor drift was negligible (n = 4, duration: 53-129 h). In situ measurements of depth, temperature, and salinity (conductivity) successfully revealed the microenvironment, and showed that Japanese sea bass often ascended from deep seawater to shallow freshwater at night. In all fish, over 99% of these excursions were completed within 10 min. The maximum duration of these excursions was about 6 h. This might be an effective strategy for temporal utilization of hypo-osmotic environments for foraging without physiological and energetic costs. This is the first report to clearly validate the accuracy of salinity measurement without sensor drift in free-ranging fish. The device and methods presented here can be applied to other euryhaline fish.

KEY WORDS: Bio-logging · Estuary · Euryhaline fish · Osmoregulation · Salinity

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Cite this article as: Miyata N, Mori T, Kagehira M, Miyazaki N, Suzuki M, Sato K (2016) Micro CTD data logger reveals short-term excursions of Japanese sea bass from seawater to freshwater. Aquat Biol 25:97-106.

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