2. Cuckoo Wrasse
It doesn’t need to be big and flesh-hungry to be fascinating, and the cuckoo wrasse is proof of that. This species is common along the coastal areas of the United Kingdom, and is famous for its species unique ability to switch sexes once it reaches sexual maturity at about five to seven years of age. In the absence of mating partners, a female can change her sex to a male in order to fill the role.