The stocky Prust did much of the fighting for the undersized team last season, but at least some of that work will now go to the six-foot-five Parros, who signed with the Canadiens as a free agent for one year at $937,500.
Beefing up was one of general manager Marc Bergevin's off-season goals.
"It's always good to have a few guys like that," Prust said Thursday. "It takes the stress away a bit.
"Some nights, the other lineup might have three or four guys and now we can match them pretty good."
Parros skated in drills wearing a no-contact jersey, but did not take part in a one-hour scrimmage as the Canadiens were on the ice for the first time in camp. He is recovering from rotator cuff surgery and hopes to be ready when the regular season opens on Oct. 1.
The scrimmage was only a few minutes old when Prust's linemate Ryan White skated off bleeding heavily above the right eye after a high stick from defenceman Greg Pateryn. He did not return.
Only a few minutes later, rearguard Nathan Beaulieu looked to injure his left shoulder when he was hit into the boards by Charles Hudon.
Coach Michel Therrien had no update on the condition of either player, other than to point out in jest that White had an "upper-body" injury.
Prust was Montreal's top acquisition for the lockout-shortened 2012-13 campaign, adding some grit as well as decent hockey skills to a team that had finished last in the Eastern Conference the previous season. He had five goals, nine assists and 110 penalty minutes in 38 games.
The London, Ont., native took on all comers, even though he is more of a middleweight by NHL enforcer standards, and helped the Canadiens rocket to second in the conference.
But the battling looked to take its toll. He missed time in March with a separated shoulder, then separated a rib during Montreal's five-game loss to the Ottawa Senators in the first round of playoffs.
Much of that work will now fall to Parros, although Prust said he'll mix it up when needed. Last season, Prust took 10 fighting majors while Parros had nine in 39 games with the Florida Panthers.
"I'm still going to go out and do the same things I did last year," said Prust. "Whether you have four heavyweights or you don't, it doesn't change a lot for me."
Parros said there is no competition with Prust.
"We've had plenty of conversations," he said. "There's nothing big there.
"We're excited to play with each other. I think we have a lot of good character on this team."
Prust spent most of last season skating on scoring lines, but he started camp on a unit of grinders with White and Travis Moen.
Only two seasons ago, Moen was doing much of the fighting for Montreal.
But last season, after Bergevin signed him to a four-year deal worth $1.8 million per season, there was less pressure to fight. Moen's offensive production plummeted to two goals and four assists in 45 games.
The 31-year-old needs to rediscover his energetic, checking game.
"With a guy like Travis, it's simple — we want to make sure he competes every night and we want him to play with an edge," said Therrien. "That's what grinders do to have success."
Therrien said he will tinker with line combinations throughout camp, but the units on the first day looked very much like the ones that could start the regular season.
With Brian Gionta recovering from a biceps injury, newcomer Christian Thomas was on right wing with the Tomas Plekanec and Rene Bourque duo.
Danny Briere, the top off-season signing, skated with David Desharnais and Max Pacioretty. Lars Eller centred sophomores Alex Galchenyk and Brendon Gallagher.
The defence pairs had Raphael Diaz with Andrei Markov, P.K. Subban with Josh Gorges and newcomer Douglas Murray with Francis Bouillon. Davis Drewiske skated with Jarred Tinrodi.
When the lockout ended in January, teams had only one week to prepare for the season. This time, Therrien is grateful to have a full camp.
"Last year was really demanding," he said. "A lot of credit goes to the players for buying into what we taught.
"There's going to be a few adjustments to the way we're going to play. The players like the way we play, so we're not going to change things too much. We're just going to tweak a couple of things that probably people won't see. But from the inside, we think we'll have a bit better success.
"A regular training camp gives young guys a chance to show what they can do. It gives me a chance to work on combinations, and that's what we'll do during the intra-squad and exhibition games."
The first scrimmage was marked by some nifty play by Louis Leblanc, who is rebounding from injuries, and from Thomas, who was obtained from the New York Rangers for prospect Danny Kristo.
Goalie Peter Budaj stoned Subban on a penalty shot.
Right-winger Sebastian Collberg, a 2012 draft pick, did not skate. He is nursing a knee injury suffered during exhibition games with the Swedish junior team last month in Lake Placid, N.Y. Therrien said the injury was "nothing major."