Fish Anatomy – The character has the form and/or characteristics of a fish.
The D&D universe has any number of fish that are quite deadly including Aquantis (Creature Collection I), Dragonfish (TSR 2102 MC1 Monstrous Compendium), Drowned Lady (Creature Collection I) and the Lurker Below (Creature Collection II. Dark Menagerie).
Abe Sapien (Dark Horse) is a humanoid fish that is Hellboy’s partner (Hellboy Seed of Destruction #2).
Aquarus (Image) is a fish like Aquaman in the Image universe (Official Handbook of the Invincible Universe #1).
Savage Dragon (Image) has three fish humanoids including Atlantean, Big Fish and Catfish.
The D&D universe has several fish like humanoids including the Pisceans (Creature Collection II. Dark Menagerie), Kuo-Tao (D&D 4th Edition – Monster Manual 1), and Sahuagin (AD&D 1st-Monster Manual).
The Lovecraft universe has the Deep Ones (Field Guide to Cthulhu Monsters).
The Deep Six (DC) are a gang of fish humanoid supervillains (DC Who’s Who #6).
Ripjaws is a fish humanoid in the Ben 10 universe.
Triton (Marvel) is a member of the Inhumans (Official Handbook of the Marvel Universe V1 #11).
Some fishy DC Silver Age action in House of Mystery V1 #94, Strange Adventures V1 #21, and Tomahawk V1 #95.
Locathah – D&D 3.5 – Monster Manual I
Locathah – TSR 2140A Monstrous Manual
Ripjaws – Ben 10
Sea Cat – D&D 3.5 – Monster Manual I
Triton – TSR 2140A Monstrous Manual
Joe Pollack (Charlton) is a fisherman that becomes a fish in Space Adventures #46.
According to Space Adventures #56 (Charlton), Jupiter has fish men.
Trading Card Games have a many types of fantastic fish.
Colo Claw Fish
Afanc – TSR 2145 Monstrous Compendium Annual Volume 1
Ascallion Fish – TSR 2173 Monstrous Compendium Annual Volume 4
Fish People – Second Doctor Sourcebook
Ixitxachitl – TSR 2140A Monstrous Manual
Ixzan – TSR 2166 Monstrous Compendium Annual Volume 3
Kuo-Tao – TSR 2140A Monstrous Manual
Lythlyx – TSR 2145 Monstrous Compendium Annual Volume 1
Saturnyians – Eleventh Doctor-Gamemaster’s Guide
Sea Glutton – TSR 2173 Monstrous Compendium Annual Volume 4
Skum – TSR 2145 Monstrous Compendium Annual Volume 1
Venus Blue Genes – “Venus on a Frag Shell” – 2000 AD #978 (1996)