I tried googling fish sex. Ended up with a wikipedia article about sex for fish. (ugh, btw..)
Also some dude named Jorma Vulli who fucked a burbot in the 70's. Go funland.
edit: what the fuck, he fucked a fish and then cooked and ate it. And made a magazine article about it.
Heh, reminds me of the Blue Planet RPG supplement Ancient Echoes which deals with Cetacean characters (yes, you can play a genetically uplifted Dolphin or Orca) and there is a small section that (no joke) talks about human/dolphin relationships and how there is the possibility of sex with Common Dolphins (being the closest in size to humans in length). And yea, its a game that touches on Transhumanism and how that would revolutionize the future. Still gross AF.....
Anyway, I love Mira's work cause it always leaves me with a warm feeling in my heart. I'm a sucker for Happily Ever After...