Reference for Bekhorot 6:7

תנינא ופיו דומה כשל חזיר הרי זה מום

We well understand R'Johanan laying down a ruling with reference to a slight blemish, for this informs us that [the law] is according to R'Huna and excludes the rulings of R'Hisda and Raba.

Jastrow