Q: SINCE WE LRARN IN YAVAMOS THAT THERE IS NO PREGNANCY FROM BIAH RISHONA THERE IS NO USE TO CONNECT THE RELATIONS TO THE BLESSING TO FISH - RATHER WE COULD SAY THAT SINCE FROM THE BIAH SHNIA THERE COULD BE PRENANCY - THAT SUIT THE BLESSING TO ADAM! (AND THAT SUIT THE FACT THAT ALMANAH HAS RELATIONS ON FRIDAY - WHICH SHE ALREADY HAD BIAH) AND THEREFORE WE DEMAND THE BIAH SHNIA TO BE ON THURSDAY EVENING
Chazal found Thursday to be appropriate for the first Bi'ah, which is the beginning of the Ishus, since that is the day that a Berachah was said to the fish. Although no pregnancy is likely to result from this Bi'ah, Chazal considered it a good Siman for the beginning of the relationship. Thus, the Berachah is for the beginning of the Ishus relationship, and not so much for this specific Bi'ah.
Dov Zupnik