拾い子 - (1) To pick up and raise an abandoned child. Also the child. (2) For children born in unlucky years, or in households where it is difficult for children to grow up, it is customary to pretend to throw them away and have others pick them up and raise them.
Edit: (2023-04-02)
I realized just now that the character's name is Tatsu (タツ), also spelled with Katakana like the title. So I'm thinking it has less/nothing to do with seahorse. I don't know how to fit in the complete meaning of 拾い子, so I went with the literal meaning of "pick up" + "child/girl". I was initially thinking "Lifting/Picking up the Tatsu", but then I thought of "Raising the Tatsu", which adds comedic value on the English side, since it parodies the title of the movie "Raising the Titanic". I.e. the Titanic would be super heavy and hard to lift, thus it's like Tamada is implying that Tatsu is super heavy and hard to lift. :D