Dear Goldfish Girl
What a fun question. You demonstrate some awareness of the comic book universes, and I'm going to go ahead and offer some probable origin stories for the different companies. DC Comics: DC Comics
is home to Batman, Superman, Wonder Woman, and thousands of other heroes. This is your stated preferred universe. DC superheroes tend to be iconic and infallible, more like gods than human beings. DC superheroes are the heroes we wish we could be, the ideal heroes (even Batman, who is a "normal" human, drives himself to a beyond human level, he's as perfect as a normal human could get, so still a god-like instead of human character).
The Goldfish Girl of DC Comics was created in the around 1942 when editors at National Periodicals (which would later become DC Comics) mandated that a young girl be added to the adventures of Aquaman
to allow kids, especially females, to relate to the stories. This is the same logic that landed Robin a role as the partner of Batman. Goldfish Girl is the precocious kid sister of the Atlantean prince, Aquaman (who was created in 1940). Goldfish Girl has mostly the same powers as Aquaman, she can breathe underwater, she can swim exceptionally fast, and she can communicate telepathically with sea creatures. This last talent has not yet fully developed, and she can only communicate with small sea creatures (like goldfish...and krill). Aquaman would not allow his kid sister to accompany him on his missions, due to the inherent danger, but when he was kidnapped by the pirate Black Jack, she rescued him with the aid of a school of goldfish. This led to her codename, Goldfish Girl, and also convinced Aquaman to allow her to patrol the oceans in search of threats, but with the understanding that she would send word back to him if she ever encountered anything dangerous and not attempt to deal with the danger herself. She, of course, regularly broke this agreement, and threw herself into every dangerous situation she could find. Her costume is patterned after Aquaman's, and consists of an orange/gold shirt with a fetching green miniskirt.Marvel Comics
: Marvel Comics
publishes the adventures of Spider-Man, the X-Men, The Incredible Hulk, and thousands of other heroes. Marvel heroes tend to have feet of clay, and be more flawed than their DC counterparts. Marvel characters we would be if we had super powers, making mistakes, complaining from time to time, and wondering if it was all worth it.
The Goldfish Girl of Marvel Comics is the niece of Namor: The Sub-Mariner
. Namor's adventures were first published by Timely Comics, which would eventually become Marvel Comics. In the early 1960s Stan Lee and several artists launched the Marvel universe of comics. Several previous characters that the company still had rights to, such as Captain America and Namor, were introduced into this new Marvel Universe. Namor is the son of a human sea captain and the princess of Atlantis (which allows him to breathe both water and air), and is now the ruler of Atlantis.
Marvel's Goldfish Girl was created when Stan Lee and Jack Kirby decided to expand the cast of characters that Namor interacted with so they could launch the character into his own solo-title after his popular appearance in 1962's Fantastic Four #4
. They included Namor's Antlantean brother, Numenor and Numenor's wife, Pasora, who have a daughter named Sumara. Whenever Namor is on the surface world his brother assumes the role of ruler of Atlantis. Attuma, sworn enemy of Namor, plots to take over Atlantis. He lures Sumara away, and kidnaps her. When Numenor and Pasora go to rescue Sumara they are killed, allowing Attuma to claim the throne. Sumara sees her parents murdered, and flees. Nearing the surface she is able to eventually contact Namor, who battles Attuma, and reclaims the throne of Atlantis. Namor sees that Sumara receives training and charges her with protecting Atlantis whenever he is away. She chooses the name Goldfish Girl as that was her mother's favorite animal. Goldfish Girl can breathe underwater, and is super-strong. She wears a golden swimsuit (after all, if all you do is swim, why would have the drag of a miniskirt slowing you down?).Image Comics
: Image Comics
was started in 1992 by seven popular artists who left Marvel and DC to start their own publishing company. These artists undertook the task of writing and drawing the comics produced by Image (imagine if seven popular writers broke away from Marvel and DC, formed a company called Text Comics, and tried to do their own drawing and you may spot the flaw in their plan). The early Image comics were all flash and no substance, usually employing large splash-pages of the whole team standing in heroic poses, with lots of little dialogue boxes around the page. The stories were generally poorly constructed and had little point other than to show of the artistic talent of the creators (as a side note: Image Comics still exists, and their current work is far different from the early days of the company described above).
The Image Goldfish Girl has no real origin story or purpose. She can breathe underwater, but it's never really established why. Mostly she swims around in heroic poses without any costume or clothing at all, but with water bubbles conveniently placed to allow the comic book to be sold in American stores.
You may choose which origin you like best.
ps (I started to write an Ultimate Marvel
Goldfish Girl origin, which involved her being Atlantean, and she and her family are used as slave labor by an oil company to work undersea drills. Eventually Goldfish Girl escapes after an accident kills all the other slaves, and she dedicates her life to stopping humanity from polluting the oceans...but then I realized this answer is already quite long).