Splashtails: Found everywhere, no bait needed
Ruby Splashtail
Sunny Splashtail
Indigo Splashtail
Umber Splashtail (rarest)
Seafoam Splashtail (night variant)

Pondies: Found in island or fort ponds, no bait needed
Charcoal Pondie
Orchid Pondie
Bronze Pondie
Bright Pondie (rarest)
Moonsky Pondie (night variant)

Islehoppers: Found near islands, no bait needed
Stone Islehopper (found at Sailor's Bounty, Cannon Cove, Shipwreck Bay, Shark Bait Cove, Crook's Hollow)
Moss Islehopper (found at Lone Cove, Wanderer's Refuge, Marauder's Arch, Thieves' Haven)
Honey Islehopper (found at Crescent Isle, Kraken's Fall, Sunken Grove, Plunder Valley, Discovery Ridge)
Raven Islehopper (rarest, found at Mermaid's Hideaway, Discovery Ridge, Shark Bait Cove, Wanderers Refuge)
Amethyst Islehopper (night variant, found at Smuggler's Bay, Mermaid's Hideaway, The Crooked Masts, Old Faithful Isle, Snake Island, Devil's Ridge)

(Source for the Islehopper locations)

Plentifins: Found in the Shores of Plenty, use earthworms
Olive Plentifin
Amber Plentifin
Cloudy Plentifin
Bonedust Plentifin (rarest)
Watery Plentifin (night variant)

Wildsplashes: Found in The Wilds, use earthworms
Russet Wildsplash
Sandy Wildsplash
Ocean Wildsplash
Muddy Wildsplash (rarest)
Coral Wildsplash (night variant)

Ancientscales: Found in the Ancient Isles, use leeches
Almond Ancientscale
Sapphire Ancientscale
Smoke Ancientscale
Bone Ancientscale (rarest)
Starshine Ancientscale (night variant)

Devilfish: Found in Devil's Roar region, use grubs
Ashen Devilfish
Seashell Devilfish
Lava Devilfish
Forsaken Devilfish (rarest)
Firelight Devilfish (night variant)

Battlegills: Found near active Skull Forts and Skeleton Ships, use grubs
Jade Battlegill
Sky Battlegill
Rum Battlegill
Sand Battlegill (rarest)
Bittersweet Battlegill (night variant)

Wreckers: Found near shipwrecks, use worms
Rose Wrecker
Sun Wrecker
Blackcloud Wrecker (found during storms at shipwrecks)
Snow Wrecker (rarest)
Moon Wrecker (night variant)

Stormfish: Found in storms, use leeches
Ancient Stormfish (found in Ancient Isles)
Shores Stormfish (found in Shores of Plenty)
Wild Stormfish (found in The Wilds)
Shadow Stormfish (rarest, found in any region)
Twilight Stormfish (night variant, found in any region)