Cathulid

Cathulid shows how a rarity label can mislead: it is Exotic, yet the wiki says it is easier to catch than most fish. When many spawn at once, a title message announces an abundance of Cathulids at the location. It lives in the Hall of Whispers inside the Cultist Lair; Squid is the bait, and the conditions are night, fog and Autumn.

At an average of 6.75 kg and 1,125 per kg, one Cathulid comes to roughly 7,594. That price per kilogram ranks 9th of 56 Exotic fish, behind Quartz Glass (1,533.333) and Starfall Glass (1,285.714) and ahead of Seasonal Glass (1,100) and Frozen Glass (966.667).

Experience comes to 8,000, 34th of 57 Exotic fish, or 208th across all 1,260, matching Scalloped Hammerhead and Cathulith and below Cave Angel Fish (11,340) and Ancient Depth Serpent (11,220). The in-game description calls it a fictional eldritch abomination whispering from the cultist depths.