Challenge your students to create a Fish Alphabet! (26 fish for the 26 letters of the alphabet)
Here are a few to get them started.
Also here is a video of Ocean Animals A-Z that the students might enjoy viewing. Many of the animals are fish but some are ocean mammals, reptiles, or invertebrates.
Fish (from video): Angelfish, Eel, Flounder, Goldfish, Hammerhead Shark, Pufferfish, Rainbow Fish, Viper Fish, X-ray fish, Yellow Finned Tuna, Zebra Shark.