Can i take 1200mg of fish oil with a multivitamin?

Yes: Yes, you can take bothe the multivitamin and fish oil supplement together. I advise 1/2 the multi in the morning and the other 1/2 in the evening. Take them all with food or after a meal.

Take oil separately: I'm not sure if you mean directly with at the same time. Fish oil has essential omega 3 fatty acids not provided in a multivitamin but is best taken as separate times than a multivitamin, as the minerals in the vitamin might combine with the fish oil to make a soap, impairing absorption of both.