Carp that soak up the sun are fitter, and bold fish benefit more by sunbathing for longer
One magic late afternoon in summer, sitting on the bank of a clear, still lake in Hertfordshire, it was possible to see lines of motionless carp on the surface that appeared to be sunbathing. The idea that fish, like snakes and other ectotherms (“cold-blooded” creatures), might enjoy or benefit from sunbathing was dismissed as a childish fancy at the time, but many decades later has been vindicated.
A scientific paper shows that carp not only sunbathe, but also gain body heat, grow faster and are fitter as a result. These fish were warmer than their surroundings despite the fact that scientists thought this was impossible because the fish were immersed in cold water. Another key finding is that not all fish gained equally. The darker fish absorbed more warmth than their paler companions and grew faster.