what kind of motor oil do i use in a 2006 sea ray sundancer 240 with a 5.0L motor

[roman599a]

I live in lake Tahoe, which is 6250 ft in elevation. The water is probably 55-69 degrees and the outside temperature seldom reaches the high 80s.. id say 75-80 is an average summer temperature. I have a merc 5.0L 265 hp motor. about 225 hrs on it..