Individual daytime swimming of mesopelagic fishes in the world's warmest twilight zone

We assessed the activity and swimming patterns of mesopelagic fishes in Red Sea using bottom-moored, upward-facing echosounders deployed at 555 700 m depth. The vertically migrating scattering layer descended close to bottom during daytime. This permitted assessment behavior depths by applying acoustic target tracking for individuals traversing beam. Swimming did not fit notion torpid daytime habitat. were moving continuously, with a prevailing downward direction before noon upward after, though both directions all times. They moreover horizontally estimated speeds ?2.1 cm s?1, suggesting ?0.5–1 body length intermittently turning. High high temperatures suggests respiration depth, considered key element active carbon pump.