All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
What is known as mermaids does not exist in reality; rather, they are part of ancient myths and legends.
The Free Encyclopedia (Wikipedia) defines mermaids as a legend. The definition reads:
“Mermaids, or in classical Arabic 'Khaylaan', or 'daughter of the sea', or 'daughter of the water'. In colloquial Arabic, it is called 'bride of the sea'. Mermaids are legendary mythical creatures which live in seas and lakes. Mermaids are depicted as aquatic creatures with features of both a human being and a fish. The upper part – which is the human part – has all the characteristics of a human being from the head to the navel, whereas the lower part – which is the fish part – has a body of a fish from the navel to the tail, and there are males and females. The mermaids are usually beautiful and enchanting, and there are many tales about them which are inherited from one generation to another.”
The Arab World Encyclopedia reads, “The mermaid is a mythical creature that is claimed to have lived in the sea. According to popular beliefs, the body of a mermaid is half human and half fish ... mermaids and water cranes are depicted as fairy aquatic creatures in art and poetry.”
Allah knows best.