This prohibition, known as mashkim megulim, “uncovered beverages,” is recorded in the Talmud(3) and codified by the Rambam as halachah which we are to practice today. But the Shulchan Aruch, who starts by quoting the Rambam, concludes by ruling that this edict no longer applies.(4) Since poisonous snakes and reptiles are rarely found in populated areas nowadays, there is no longer any reason to forbid drinking an uncovered, unsupervised beverage. The basic halachah follows this opinion and one is no longer required to concern himself with this prohibition.(5)
3 Avodah Zarah 30a and Chulin 9b. The original source is a Mishnah in Terumos 8:4.
4 Y.D. 116:1, based on the view of Tosfos, Rashba and Tur.
5 Mishnah Berurah 160:23.
where in the Shulchan Aruch do we find that the matzav of fish and meat together is no longer a sakana?
what is the logic even (similar to that of venemous snakes not being common any longer) that meat-fish is no longer a sakana?
where are the studies by modern physicians that demonstrate that meat-fish is not dangerous?
all we have an assumption, not based on any investigation by modern medicine, that it is not dangerous, perhaps because they assume it to be merely an ancient superstition.
and even so, where can you find any statement in a medical journal or other medical media that it is not dangerous?
i imagine if you ask the majority of medical practioners whether or not eating shrimp can cloud your cerebral processes, they will answer no. we dont even know for sure in what sense meat-fish is a sakana, physically, spiritually or both.
i believe that is the difference between the repealing of the Takanah on uncovered water (some Poskim actually hold it still is in effect) and the still existent Takanah on meat-fish.