Validation of daily increment formation in otoliths of immature and adult Japanese anchovy <Emphasis Type="Italic">Engraulis japonicus</Emphasis> |
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Authors: | Shigenobu Namiki Hiroshige Tanaka Satoshi Katayama Osamu Funaki Ichiro Aoki Yoshioki Oozeki |
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Institution: | (1) Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan;(2) Seikai National Fisheries Research Institute, Fisheries Research Agency, Nagasaki Nagasaki, 851-2213, Japan;(3) Coastal Fisheries and Aquaculture Division, National Research Institute of Fisheries Science, Fisheries Research Agency, Yokosuka Kanagawa, 238-0316, Japan;(4) Kanagawa Prefectural Fisheries Technology Center, Misaki Kanagawa, 231-0021, Japan;(5) Fisheries Research Agency, Nishi-ku, Yokohama Kanagawa, 236-8648, Japan; |
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Abstract: | In order to validate daily increment formation in otoliths of immature and adult Japanese anchovy Engraulis japonicus, three rearing experiments using chemical marking of otoliths were conducted on adult anchovy in summer 2004 and immature
anchovy in summer 2005 and in winter 2006. In the two experiments conducted in summer, the number of otolith microincrements
between alizarin complexone (ALC) marks showed that microincrements were formed daily. In the summer 2005 experiment, immature
anchovy under conditions of reduced daily food rations also showed daily microincrement formation. Average increment width
was 0.9 μm in adults and 1.8–3.1 μm in immature anchovy. In contrast, no clear increments were observed between ALC marks
on the otoliths from the experiment in winter 2006, and scanning electron microscope (SEM) observations failed to confirm
clear increment formation. We consider that low water temperatures (<13–14°C) restricted otolith growth and lowered the contrast
between the discontinuous and the incremental zones of the otolith increments. For age estimation of Japanese anchovy, clear
increments wider than about 1 μm in the otolith can be regarded as daily increments. However, daily age estimation of immature
and adult anchovy that experience low water temperatures in winter may be difficult due to the obscurity of the increments. |
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