To be very Frank there is no science backing this and yes my parents and all ancenstors have told this...but there are huge no of fish recipes which are cooked with milk and milk products.
But if you have allergy for either of these individually I would say that's a different case.
Next Steps
Try to avoid as much as possible because not much evidence is there on either end to support it's good or bad but it will always play role when it's a Nocebo effect.
Answered2021-11-19 12:14:19
Let others know if this answer was helpful