Among the seafoods, how many of them have an order quantity of more than 50?
"Seafood" is the CategoryName; order quantity of more than 50 refers to Quantity > 50
SELECT COUNT(T1.ProductID) FROM Products AS T1 INNER JOIN `Order Details` AS T2 ON T1.ProductID = T2.ProductID INNER JOIN Categories AS T3 ON T1.CategoryID = T3.CategoryID WHERE T3.CategoryName = 'Seafood' AND T2.Quantity > 50