It's the first meaning of it.
Like in French "piscine" (meaning a swimming pool) was first a pool for fish (in the ancient time).
Piscis (fish) -> Piscina (pond) -> Piscine (French): fish pond -> Piscine (Swimming pool)
I give this example, because I met it in old books, but it's very likely the same thing for Italian, Spanish & Portuguese.
Before meeting this use of "piscine" in old books (medieval times), I though that it was called "piscine" because we swim like fish!
In an old French book, from 1580, they say that this place was dedicated to fish in the very old time, and that the Romans started to call "piscina" every artificial body of water, some were used for the fish, but other ones was used to wash and to swim (both), with cold water or hot water in private houses, and even the Roman therms were called "piscina".
Source (in old French): https://archive.org/stream/cinsiologieousci1934dall/cinsiologieousci1934dall_djvu.txt
According to Gaffiot, even a drinker for animals is a piscina, and even a water tank is a piscina. So it confirms.
Piscina = (artificial) body of water.
Yes. The Romans advocated swimming (for boys and men, at least) and many baths had a pool for swimming (although often a lot smaller than modern swimming pools). One of the areas of Rome over 2000 years ago was named after a public pool which included a swimming pool:
Whether one chooses to use "pond" or "pool" (in isolation) doesn't really matter. It's a largely a question of idiolect / regional usage what people call a body of water smaller than a lake but big enough for swimming in -- although the expressions "fish pond" and "swimming pool" do vastly outnumber the reverse collocations.
It looks like a "pond for raising fish" is the first meaning, in Latin (explaining why "piscis" is at the root of the word); the meaning "pond, for bathing or swimming" is post-Augustan (it's in Suetonius, Pliny, Seneca, and the Vulgate Bible). Information from Lewis & Short.