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Fig. 27. Ontogenetic changes in specific gravity of Anguilla japonica during its early life history. The specific gravity values of 6 batches of eggs (about 1 mm in diameter) that hatched 46 hours after fertilization at 22°C (green circles). The specific gravity values of preleptocephali are means of 10 specimens of 6 batches (light blue triangles). Symbols of the other stages are leptocephalus (blue diamonds), metamorphosing leptocephalus (purple triangles) and glass eels (red circles), that represent individuals from at least 3 larval batches. The two horizontal broken lines indicate the specific gravity of seawater at 26°C (upper: 1.023) and 22°C (lower: 1.024), which roughly correspond to the water temperatures at depths of 100 and 200 m in the North Equatorial Current (15°N, 140°E), respectively. Reprinted with kind permission from Springer Science + Business Media: Marine Biology, Positive buoyancy in eel leptocephali: an adaptation for life in the ocean surface layer. 156, 2009, 835–846. Tsukamoto K, Yamada Y, Okamura A, Tanaka H, Miller MJ, Kaneko T, Horie N, Utoh T, Mikawa N, Tanaka S. Figure 2. © 2009, Springer-Verlag.

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