Suggestions:
Rare fish (goldfish or tropical fish)
Oysters (and pearls with small percentage)
Mussles
Crabs
Crayfish
Lobbster (different variants like rare blue lobster)
Roe
Aquarium
Fishpond with stats like the greenhouse for example ... needs at least 10x10x4 waterblocks to enable fish breeding
Fishing net
Fishing trap
Sushi (makes rice more useful)
Seaweed (for sushi of course)
Stews of sea life
Worm bin (rotten food into bait for fishing)
Hooks forging of different materials