Whenever you are interested in Porto Moniz and things to do there, you are bound to hear about the "Madeira Aquarium". It is the only aquarium on the island and is built on a reproduction of the São João Batista fort. It opened in 2005 and consists of 11 tanks, one of which is large, and houses around 70 species. A visit of about 10-15 min. 25 if you take your time and are passionate about underwater life.
Some of the species that can be found here? Many fish, such as the conger eel (it looks a lot like the moray eel), a ray, a small shark, and many sea stars, shells, sea urchins...
Personally, I admit I'm not particularly interested in this museum, I've already had the opportunity to visit a very large one in Genoa and I find the price of the Porto Moniz aquarium a bit excessive, like most museums in Madeira anyway, even if somewhere you have to maintain this place and feed all these fish, and financially it must be difficult.
Most of the reviews on the internet agree: an excessive price for a very small aquarium. To be done if you don't know what to do to kill time, or if the weather is really bad.