What's the difference?

 

Parshas Hashavua ראה כל אשר לו סנפיר וקשקשת תאכלו The Gemoro (חולין ס"ו) says “Akunas, is a type of fish that loses its scales when it is taken out of the water. It is kosher because it was born with scales.   The ערוך writes that דייני ישראל need to verify that it is indeed  the Akunas Fish, only then may you eat it.  The Gemoro (Chulin 63b) says that a hunter is trustworthy to say that his Rebbe told him that this particular bird is kosher. The Gomoro says his Rebbe refers to his hunting teacher. (not his Rov) Why for identifying kosher birds we don’t need a Rov and to identify kosher fish we do need a Rov?