This stricture does happen to be present in Kashrut or Jewish Kosher law, since the mixing of meat, fish and dairy is prohibited... so if one is not Hassidim or otherwise observant or entertaining those that are such there is, obviously, no problem...
Sounds like jibba jabba to me.. the person who told you that is a fool
Moules Mariniere... sometimes uses cream (depends on who's cooking it)
Cod in butter sauce
seafood chowder
Monkfish with a mushroom cream sauce
Pan-fried cod on a bed of pea puree with smoked bacon and shallot cream sauce
Kedgeree
Lobster thermidor