Most fish n' chip shops give you options for the fish you can have - flake or other cheap fish (at our local it's cod) are the default fish, but you should be able to ask for a fillet of any other kind of fish you like, battered or crumbed, you just pay a little bit extra for it, itms :) I ate stacks of fish and chips when pregnant, both times we lived in houses where there was a fish and chip shop within 200m lol :D
I avoided shellfish (I was DEVO, love the stuff!) during pgs but made up for it by eating buckets of potato scallops instead of the fishy ones ;)
Enjoy your fish & chips, you've just made me huuungry! Haven't had it in ages! :D