That is a typo. Because some lines higher, you can find a masculine pronoun referred to крючок. It should be
1"и увидели на нём ".
2.И, полный решимости, только слегка побледнев, он подплыл к крючку Соня и взял его в рот.
This is another typo in the same story. They are the author's typos.
А я подражаю дамам. Быть может даже, я сам дама и только скрываюсь под мужским псевдонимом.
And after reading these lines, I am inclined to think he did it on purpose. Just as a stylistic device or literary device. Gender-play. He wrote this story as a parody on women's stories about nothing and included typos intentionally.