are these safe to take?

I'm 6 weeks & 5 days pregnant! & i just ordered some prenatal vitamins off of amazon & im supposed to get them today! But the vitamins don't have DHA in them! So I saw some gummy vitamins at CVS called "olly alpha & omega"! It has DHA, EPA, fish oil & omega 3's! BUT the ingredient is TUNA! I know tuna has the mercury! So... I mean are these safe to take???? If not, what's a good supplement to take for DHA & omegas! I'd rather it be gummy or chewable bc I have a hard time taking pills!