Portuguese defender Fonte, 30, has pledged his future to the St Mary's outfit and will remain at the south coast club until at least 2017.
"We are very happy because we like to keep the good players and the experienced players," Koeman said
"Jose is the captain for this season on the field
We have another captain of the club - Kelvin Davis - but Jose is the captain on the pitch.
"I am very pleased about his new contract, which shows our ambition and the philosophy of the club and I am happy about that."
Saints have lost the services of defenders Luke Shaw, Calum Chambers and Dejan Lovren, strikers Rickie Lambert and Dani Osvaldo and midfielder Adam Lallana this summer.
Fonte, however, has chosen to remain, and said: "I'm very excited to be signing this new contract for another three years
This is where I feel at home.
"I've been very successful at this club so it was an easy decision.
"What made me sign was first we signed a very good manager, second, the fans have been great for me - they love me and I have a good relationship with them.
"And third we have a lot of quality in the team and we will try to do even better than last season if we can."
Source : PA
Source: PA