Preliminary report of swimming behavior and the response to temperature of lacustrine masu salmon, Oncorhynchus masou Brevoort, monitored by data logger during the spawning migration in Lake Toya

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Swimming depth and ambient water temperature of male masu salmon (Oncorhynchus masou Brevoort) during the spawning migration in Lake Toya was examined using a micro data logger. Soon after release, the fish swam along the coast and mean swimming depth and water temperature were 14.2±7.96m and 13.8±3.80℃. Then, the fish swam into a stream where mean swimming depth and water temperature were 1.6±3.28m and 18.3±1.58℃. The fish returned to the lake again where mean swimming depth and water temperature were 33.4±14.1m and 5.5±1.45℃. Finally, the fish swam into a stream again and stopped any vertical movements. The results show that the fish swam in coastal waters at a higher water temperature despite the likely higher energy expenditure and swam in deep, cooler water to recover between two upstream migration attempts. We hypothesize that temperature is not an important parameter for upstream migration and probably navigational mechanisms and hormonal motivation for spawning have affeted ambient temperature selection in lacustrine masu salmon during the spawning migration.
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