Making seviche - the citrus cooks the fish w/o heat?

I just bought some halibut to make seviche (or ceviche) without really looking at the recipe… then I found out the citrus from the lime, lemon and orange juice “cooks” the halibut when marinated in the fridge for 4 hours. Because of this the halibut has to be fresh; I bought it at the fish/seafood counter at my local grocery store (it’s not frozen), so that works right? I never knew you could cook something with citrus juice. I don’t wanna get myself and my family sick…

Thanks.