Leedsichthys

Leedsichthys, also known as Leeds' fish, is a giant member of the Pachycormidae, a group of Mesozoic ray-finned fish that lived in the oceans of the Middle Jurassic period. Today, many subspecies of Leedsichthys live in today's oceans worldwide, ranging from 29.5 footers to gigantic 98, about the size of the outdated size for the prehistoric populations of Leedsichthys. They are peaceful (gentle) giants towards humans, dylanuses, and other sapient beings, feeding only on krill and plankton. They were once found in the seas of Jurassic Europe and South America, but now, since their resurrection back to life through time travel, they thrive in today's oceans worldwide except the Arctic oceans and Antarctic oceans (where these seas are too cold for Leedsichthys to live in). For such giant animals, Leedsichthys are supprisingly easy to keep and breed in captivity.

In today's seas
Like the largest fish today, the whale sharks and basking sharks, Leedsichthys problematicus derives its nutrition as a suspension feeder, using an array of specialised gill rakers lining its gill basket to extract phytoplankton, zooplankton, and small animals from the water passing through its mouth and across its gills. Leedsichthys is a ram feeder, making the water pass through its gills by swimming, but can also actively pumped the water through the gill basket. In life, Leedsichthys is cold-blooded and grows up relatively slowly, reaching to their adult size in 15 years. Their metabolism is slow, which is also a reason why these fish grows slowly. The main predators of Leedsichthys includes predatory dolphins (including orcas), sharks (especially great white sharks), sealsnakes, resurrected Mesozoic species of plesiosaurs, resurrected pliosaurs, resurrected mosasaurs, some dragon species (including thunderdrums, which attacks young Leedsichthys), and some others.