The Serie A side see both sides of loan agreements as Alvarez heads to La Liga while 'keeper Juan Carrizo arrives to the Rossazzurri from Lazio.
The 27-year-old has struggled to impose himself at Catania since his arrival in 2008, making just six Serie A appearances since the start of the season.
He joins Zaragoza with the task of helping the Blanquillos avoid relegation as they sit at the bottom of the table, with a mere 12 points from 20 matches.
Nevertheless, Catania have signed Lazio goalkeeper Juan Pablo Carrizo on a six-month contract, with aim to make a more permanent deal in the summer, depending on performances.
The 27-year-old custodian has been unable to make his mark at the Stadio Olimpico, spending the last two seasons on loan at Zaragoza and River Plate.