This is the 391st most frequent Catalan word.
viu
"Viu" means "alive" or "living."
Here, 'viu' is the third person singular present indicative form of the verb 'viure', meaning 'to live'.
Ell viu a Barcelona.
He lives in Barcelona.
In this case, 'viu' is an adjective meaning 'live' or 'alive', describing the state of the fish.
És un peix viu.
It is a live fish.
Here, 'es viu' is a reflexive construction of the verb 'viure', used to convey the experience or ambiance in concerts.