The Merrow are the Scottish and Irish Gaelic beings who are human from the waist up and fish from the waist down.
Though the Merrow are reported to be capable of falling in love with humans, their ultimate love is the sea, where they eventually return to.
Merrow-women were reported to be quite beautiful, whereas Merrow-men are ugly, which lead to the women seeking out human husbands. Occasionally the men would trick the women to staying with them by stealing their cap or capes, which allowed them to stay under water. The women would thus be forced to stay with the human husband until their found their cap or cape, and would then promptly abandon her family.