i have fed a lot of people but abput 1 and 1/2 pounds per person is about right.
My wife and i eat a lot of fish and i bag 8 fillets in a bag that is enough for 2 people with some left over if you serve with potatoes hush puppies and beans. that is plenty so 4 fillets are plenty per person.
if you serve 10 they had better be very small fillets or you will have a lot of waste. Thats 5 whole fish per person.