[5][6] Most tales of the sort begin with the father catching a talking fish thrice and, in the third time, the animal asks to be sacrificed and fed to the fisherman's wife and horses, and for his remains to be buried underneath a tree.

The many-headed serpent enemy shares similarities with Greek mythic creature Hydra, defeated by Heracles as part of his Twelve Labors.

An episode of a battle with the dragon also occurs in several fairy tales: The Three Dogs, The Two Brothers, The Merchant (fairy tale), The Bold Knight, the Apples of Youth, and the Water of Life, The Three Princes and their Beasts, The Thirteenth Son of the King of Erin, Georgic and Merlin, the epic feats of Dobrynya Nikitich, the Polish legend of the Wawel Dragon.

Greek folklorist Georgios A. Megas [el] listed several conflicting theories that different scholars have proposed for the origins of the tale type (ATU 303): some see a possible connection with the Ancient Egyptian story Tale of Two Brothers; Waldemar Liungman [sv] suggested a origin in the Byzantine period (300-1500 CE); Wolfgang Hierse indicated the Eastern Mediterranean, during the Hellenistic period.

[20] German scholar Kurt Ranke, who authored one of the definitive studies on the tale type ATU 303, analysed some 770 variants.

As researcher Richard M. Dorson put it, the tale type "is well distributed throughout Europe and densely reported from Finland, Ireland, Germany, France, and Hungary.".

[31] According to Kurt Ranke, in Enzyklopädie des Märchens, the "constitutive" element of tale type ATU 303 is the twins' birth either by their mother drinking magic water or eating a wonderful fish or apple.

[38] Similar variants include Le rei des peiches, from Bélesta, Ariège, wherein triplets are born from the magical fish;[39] and Polish "О рыбаке и трех его сыновьях" (English: "About the Fisherman and his Three Sons"), where the fisherman catches, as third try, a fish with diamond scales and gills that engenders the human triplets.

[40] In Czech fairy tale The Twin Brothers, the enchanted fish is described as a princess cursed into piscian form.

The youth escapes with a horse, dips his body in a river of a golden colour and works as gardener in another kingdom (tale type ATU 314).

[54] The ATU 303 type usually involves the birth of twins (or triplets), but in variants there are born two similar-looking individuals from a rich mother (queen, lady) and a poor one (maid, servant), who both ate the magical item that, according to some in-story superstition, is said to have pregnancy-inducing properties, such as a fruit or herb.

[58] In the Moravian tale Zkamenělí lidé ("The Petrified People"), a princess and her friend, a burgermeister's daughter, drink seawater and become pregnant at the same time.

Seven years later, the king suspects foul play and plans execution of the maidens and their incredibly similar children, Petr and Karl.

[59] In a Russian fairy tale, when the fisherman gives the fish for his wife to eat, she shares the food with the mare and the cow.

[60] In an Irish tale published by poet W. B. Yeats from an "old man" in Galway, Jack and Bill, the king's wife and a female cook eat a fish and give birth to identical individuals.

[63][64] In a Swiss tale collected by author Dietrich Jecklin from Schlans with the title Von den zwei Freunden ("About the two friends"), intent on never marrying his daughters, a king isolates them in a palace he built for them on a remote island.

According to Swedish scholar Waldemar Liungman [sv], the heroes' water-related names are a "reminiscence" of their origin either through the fish or by water.

[72][73] The tale of brothers Brunnenhold and Brunnenstark was also given a somewhat abridged format by 19th century theologue Johann Andreas Christian Löhr, with the name Die Söhne der Quelle.

[74] In a Russian-language Siberian variant titled "Федор Водович и Иван Водович" ("Fyodor Vodovich and Ivan Vodovich", or "Fyodor, Son of the Water, and Ivan, Son of the Water"), a queen gives birth to a daughter, much to her husband's chagrin.

[77] The general narrative of the tale type separates the twins: one defeats the dragon and, after he marries the princess, goes to an illuminated castle (or tower) in the distance, where a witch resides.

[86][87] In a tale collected from Wallonia, Le Garçon avec Ses Trois Chiens, triplets are born from the ingestion of the fish's flesh.

This variant is peculiar in that it inverts the usual narrative: the brothers' petrification by the witch occurs before the episode of the dragon-slaying.

[89] In another tale, Die zwei Brüder ("The Two Brothers"), the heroes are born after the ingestion of the fish, one stays home and the other goes around the world.

In this story, the episode of the petrification in the castle of the witch happens after the killing of the dragon, but before the revelation of the false hero.

[90] In an unsourced tale published by Andrew Lang in his The Grey Fairy Book, The Twin Brothers, an old woman reveals that the infertility of a fisherman's wife can be cured by ingesting the flesh of a gold-fish, and after some should be given to her she-dogs and mares.

When the older twin leaves home, he arrives in a kingdom and tries to woo the princess Fairest in the Land, by performing her father's three tasks.

[92] This tale was originally collected in German by Austrian consul Johann Georg von Hahn from Negades, with the title Die Zwillingsbrüder.

[93] Some variants skip the birth implement altogether and begin with the twin (triplet) princes going their separates ways at the crossroads, after they gather their animal retinues.

[94] The tale type was adapted into the story Los hermanos gemelos ("The Twin Brothers"), by Spanish writer Romualdo Nogués, with a moral at the end.

One boy rides forth and marries a girl from a village, and another stays at home, until he has to rescue his twin from a witch's petrification spell.