The aquarium in Dr No (1962) was fake. To create it, the production team projected some stock footage of fish onto a screen. However, they only had footage of small fish, so they maximised it. In-universe, the villain explains that the glass of his aquarium has a “magnifying effect”.
Movie effects can be pretty incredible when you finally find out the technical wizardry that goes into it. And if it’s like Star Wars, they mostly involve tiny versions of things.