Leedsichthys are the biggest fish that appeared in the Jurassic period. It grew to 27 meters long, and sometimes larger, making it the largest bony fish to ever live. It apart from the Blue Whale is the only animal to rival Liopleurodon in size, although dinosaurs like Seismosaurus were much longer, but they weren't as heavy.
A Leedsichthys plays a minor role in Sea Monsters: A Walking with Dinosaurs Trilogy. While visiting the second most dangerous sea, Nigel Marven swims with some Leedsichthys, and watches a Liopleurodon eat one of them. Hybodus and Metriorhynchus are also seen attacking and eating bits off the Leedsichthys.