Embryonic development and larval behavior of the kissing loach (<Emphasis Type="Italic">Parabotia curta</Emphasis>): adaptations to an ephemeral,hypoxic environment |
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Authors: | Tsukasa Abe Tatsuya Sakamoto |
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Institution: | (1) Ushimado Marine Laboratory, Graduate School of Natural Science and Technology, Okayama University, 130-17 Kashino, Ushimado, Setouchi 701-4303, Japan;(2) Present address: LAGO Co., Ltd, 396-2 Taga, Omihachiman 523-0821, Japan |
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Abstract: | Many teleost fishes in lowland fresh waters spawn in ephemeral flooded areas, the bottoms of which are prone to hypoxia. Little
is known about how embryos and larvae deal with these potentially hostile environments. This study examines the functional
and behavioral ontogeny of one such species, the kissing loach (Parabotia curta). Kissing loach eggs are demersal and adhesive. Hatching occurs at 24.8 ± 0.1 h post-fertilization at 25°C, much earlier
than most fish species. The newly hatched larvae are precocious with no functional mouth, fins or eye pigmentation. Swimbladder
inflation normally occurs at about 4 days posthatch, even before which the hatched larvae moved immediately toward the water
surface to hang from water moss. Experiments with larvae 20 h after hatching showed that they spent significantly less time
on the bottom in hypoxic water (2 mg/l) than in normoxic water, and suggest that hypoxia is a major directive factor in eliciting
surfacing behavior. For the kissing loach, we have previously reported short-term spawning after the formation of flood areas
as well as wide scattering of the spawned eggs in the temporal flooded areas. These traits with the present results of hatching
at an early stage and the immediate upward movement of larvae are considered to be effective strategies for using ephemeral,
hypoxic flooded areas for reproduction. |
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