Why is the pike the main fish in Russian folk tales?

In Slavic mythology, the pike is a dual, borderline creature. Not only is it constantly preoccupied with life and death, it also acts as a mediator between the hereafter and this world, the world of the dead and the world of the living. This requires not only its ability to perform miracles, but also its connection with pregnancy or, more precisely, with extraordinary conception. All of this fish's qualities are reflected in Russian folk tales.

In the fairy tale ‘Ivan the Cow's Son’, a royal couple gives birth to a long-awaited heir after the queen eats a magical "golden-finned pike". The magic of the magical fish is so powerful that even servants become pregnant simply by licking a spoon with scraps of food. Water and moisture, in general, are associated with feminine nature in folklore. Consequently, fish living in water –  the element associated with the birth of life and the afterlife – were themselves perceived as vessels for souls awaiting birth. By eating them, a woman would receive a soul for her future child.

But, the pike's magical powers extended beyond matters of procreation and were widely used in practical magic: the fish's teeth and jaw were considered powerful amulets. They were hung over the entrance to the house to protect against evil and disease, taken fishing for good luck and used in hernia charms (the ‘golden pike’ seemed to "gnaw out" the ailment with its teeth).

However, the leading role went to this fish in the fairy tale ‘By the Pike's Command’. In it, it’s a powerful being, bestowing magical powers on the village idiot Yemelya. He catches a fish, it asks him to let it go and, in gratitude for his kindness, it casts a spell that grants any wish he may have. And Yemelya makes full use of it, both for good and evil. Nevertheless, in the end, it is this spell that makes him the tsar's son-in-law and the tsar's daughter's husband.