A transgender fish fought a brutal stand-off with a rival male during the compelling first episode of David Attenborough's eagerly anticipated Blue Planet II. The award winning series returned to BBC One this evening, 16 years after its first season wowed viewers in 2001. After the shocking scenes in Sir David's Planet Earth II, which included a snow leopard being'raped' and a lizard making a seemingly impossible escape from an army of snakes, the broadcasting legend set a high bar. While the opening episode of his new series did not measure up for drama, it certainly delivered on the unexpected. Whisking viewers off to the coast of northern Japan, Blue Planet II revealed the bizarre mating ritual of the Asian Sheepshead Wrasse - a transgender fish.