Leviticus 7:26-27 teach us about the prohibition to eat blood, whether it be of fowl or of beast, in any of the dwellings.
So is one allowed to eat the blood of the fish? Is one allowed to eat blood outside of our dwellings? Is one allowed to drink the blood (seperated from the meat)? And last but not least am I allowed to suck the blood up of the bleeding finger of my child?
In regards to eating the blood of a fish, the Rambam in Mishnah Torah, Ma'achalos Asuros 6:1 writes:
אֲבָל דַּם דָּגִים וַחֲגָבִים וּשְׁקָצִים וּרְמָשִׂים וְדַם הָאָדָם אֵין חַיָּבִין עָלָיו מִשּׁוּם דָּם. לְפִיכָךְ דַּם דָּגִים וַחֲגָבִים טְהוֹרִים מֻתָּר לְאָכְלוֹ וַאֲפִלּוּ כְּנָסוֹ בִּכְלִי וְשָׁתָהוּ מֻתָּר.
But the blood of fish and grasshoppers, and shkatzim and ramasim and the blood of a human, one hasn't violated the prohibition of consuming blood. Thus the blood of the fish and tahor grasshoppers are permitted to eat, even if one gathered it into a vessel and drank it
The Shulchan Aruch (YD 66:9) codifies this but only allows it if a certain condition is met:
דם דגים אף על פי שהוא מותר אם קבצו בכלי אסור משום מראית עין לפיכך אם ניכר שהוא מדגים כגון שיש בו קשקשים מותר:
The blood of fish even though it is permitted if they are collected in a vessel is forbidden because of appearances, so if it is clear that it demonstrates such as having scales allowed
Bottom line: it's allowed provided you drink it with fins/ scales near it so there would be no issue of "maras ayin."
