פירוש על עבודה זרה 79:3

The rules regarding the brine are more lenient than the rules regarding eating the fish itself. To eat the fish itself, one needs to be able to see the head and backbone.

R. Zera seems to hold like R. Huna, according to whom the head and backbone must be recognizable. But he used to think that the disagreement was over eating the fish itself. R. Huna would have agreed that when it comes to dipping in the brine, only one sign of its kashrut is needed. But then when he heard that they disagree over dipping in the brine, and that R. Huna said that even then both signs are needed, he stopped dipping in the brine.