Praise be to Allaah.
A mermaid is a creature that lives in water and looks like a human. As to whether it really exists or it is a mythical being, that is subject to further discussion.
It says in a footnote in al-Mawsoo’ah al-Fiqhiyyah (5/129): From the modern academic resources that are available to us, it may be understood that the mermaid, which is called Sirène in French, is a mythical creature that is described in fairy tales as having an upper body like a woman and a lower half like a fish.
See the French Larousse encyclopédique on the word Sirène.
The encyclopaedia goes on to say: The widespread notion in ancient times was that the wonders and animals of the sea were more and greater than the wonders of dry land, and that there was no kind of animal in the sea that did not have a counterpart on land. This was confirmed by Prof. Muhammad Fareed Wajdi in his encyclopaedia, quoting from modern academic sources. See: Daa’irah Ma’aarif al-Qarn al-‘Ishreen: Bahr – Hayawiyan. End quote.
Al-Dumayri said in Hayaat al-Haywaan al-Kubra: Mermaid: it resembles a human but it has a tail. Al-Qazweeni said: Someone brought one of them in our time. End quote.
Many of the fuqaha’ mentioned mermaids and differed on the ruling concerning them. Some of them said that they are permissible (to eat) because of the general meaning of the evidence which says that whatever is in the sea is permissible. This is the view of the Shaafa’is and Hanbalis, and is the view of most of the Maalikis and of Ibn Hazm and others. And some of them regarded it as haraam because it is not a kind of fish. This is the view of the Hanafis and of al-Layth ibn Sa’d.
Ibn Hazm (may Allaah have mercy on him) said in al-Muhalla (6/50): As for that which lives in the water and cannot live anywhere else, it is all halaal no matter what state it is in, whether it is caught alive and then dies, or it dies in the water and then floats or does not float, whether it was killed by a sea creature or a land animal. It is all halaal to eat, whether it is the pig of the sea (i.e., a dolphin), a mermaid, or a dog of the sea (i.e., shark) and so on. It is halaal to eat, whether it was killed by an idol-worshipper, a Muslim, a kitaabi (Jew or Christian) or it was not killed by anyone. The proof of that is the verses in which Allaah says (interpretation of the meaning): “And the two seas (kinds of water) are not alike: this is palatable, sweet and pleasant to drink, and that is salt and bitter. And from them both you eat fresh tender meat (fish)” [Faatir 35:12] and “Lawful to you is (the pursuit of) water game and its use for food — for the benefit of yourselves and those who travel” [al-Maa’idah 5:64]. Allaah spoke in general terms and did not exclude anything, “and your Lord is never forgetful” [Maryam 19:64]. End quote.
Al-Durayr – a Maaliki scholar – said in al-Sharh al-Sagheer (2/182): Sea animals in general are permissible, whether it is dead meat or a ‘dog’ (shark) or a ‘pig’ (dolphin), and they do not need to be slaughtered properly. End quote.
Al-Saawi said in his commentary on that: The words “or a ‘dog’ or a ‘pig’ also include a ‘human’, referring thereby to mermaids. End quote.
Al-Nawawi – who was a Shaafa’i scholar – said in al-Majmoo’ (9/33): As for that which does not appear in the well known form of a fish, the correct view according to our companions is that everything (from the sea) is permissible, because the correct view is that the name fish may be applied to all of it, and Allaah says (interpretation of the meaning): “Lawful to you is (the pursuit of) water game and its use for food” [al-Maa’idah 5:64]. Ibn ‘Abbaas and others said: Its game is that which is hunted and its food is that which the sea throws out. And the Prophet (peace and blessings of Allaah be upon him) said in the saheeh hadeeth: “Its water is a means of purification and its dead meat is halaal.” End quote.
Al-Mardaawi – who was a Hanafi scholar – said in al-Insaaf (10/364): All sea animals are permissible, except frogs, snakes and crocodiles. End quote.
Al-Kaasaani – who was a Hanafi scholar – said in Badaa’i’ al-Sanaa’i’ (5/35): As for that which lives in the sea, there is no animal in the sea that is haraam to eat except in the case of fish, it is permissible to eat it except that which floats. This is the view of our companions (may Allaah be pleased with them). End quote.
Ibn ‘Aabideen – who was a Hanafi scholar – said in Radd al-Muhtaar (6/307): Anything other than fish and the like, such as mermaids and dolphins, is impure and remains prohibited.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said, after stating that it is more likely that it is permissible to eat crocodiles and sea snakes: The correct view is that nothing is excluded from that, and that all the sea creatures which can only live in water are halaal, alive or dead, because of the general meaning of the verse – i.e., “Lawful to you is (the pursuit of) water game and its use for food” [al-Maa’idah 5:64]. End quote from al-Sharh al-Mumti’ (6/327). Fajr edition.
And Allaah knows best.