The tighthead prop is entering his seventh season at Tigers and has already topped 120 appearances for the club.
But the opening pre-season fixture in the Channel Islands was the first time he had run out at the head of the team.
“Richard Cockerill told me early last week about being captain and for me it was a great honour,” said Castro.
“It is not a Premiership game or a European game, but it is a massive honour to captain a Leicester Tigers team.
“It is not an ‘official’ game, but to me it is official.”
Tigers scored six tries in a 34-21 triumph, completing a hat-trick for Captain Castro after leading Italy to victory over Canada and the USA during the summer.
“I have now played three games as captain in my life and won three. It is time to stop so I never lose a game!” he said.
“Normally the players and coaches they tell me to stop talking on the pitch. I think it is just because of passion for the game and sometimes you talk too much. But this time as captain I was allowed the talk. I enjoyed it very much.
“But I didn’t have to make a speech after the game. Guys like Chutes and Jordan Crane, they say they wouldn’t let me because they don’t understand my accent!”
Tigers continue the pre-season programme against Ulster in Belfast this Saturday before hosting Nottingham at Welford Road on Saturday, August 25 (3.00pm).