The shots of the young Ophthalmosaurus chasing fish were taken from an older BBC documentary in which penguins chased fish. The penguins were simply erased from the shot and replaced with CG Ophthalmosaurus, ensuring realistic interaction with the fish.
Although Liopleurodon in this episode is depicted as being much larger than in real life (25 m as opposed to 10 m), a 15 m long juvenile pliosaur found in 2002, the "Monster of Aramberri", is possibly a Liopleurodon.
Many people would argue that the rise in Liopleurodon's popularity can be attributed to this episode's portrayal of the animal. For example, nearly all of the toys that came out after it had aired carried the same color scheme it had in the show.
Aside from its highly dubious increase in size, the Liopleurodon's weight has also been drastically overestimated. The narrator claims it weighed 150 tons, but more recent studies indicate it wouldn't have been bulky enough to weigh as much. A couple of tons seems to be a more likely estimate, given that we now know that the animal was much smaller than previously thought, though if it had grown to 25 meters, (as the episode suggests) it would have still weighed certainly less than 150 tons.
Although the narrator claims that ichthyosaurs were unique among marine reptiles for giving live birth, we now know that most if not all marine reptiles were likewise viviparous. This is because recent fossils have shown that their anatomy didn't allow them to pull themselves onto dry land.