fish while pregnant?

so i kinda been craving fish alot an my sister said that i should stay away from fish since im pregnant she said its not good for the baby idk if i believe her cause ive seen alot of pregnant women eat fish but ive been listening to her cause shes had 3 kids an knows what to eat an what not this is my first so i really dont know much so i was wondering what yall thought abt eating fish is it true is it bad for the baby