His wealth may also be the cause of his undoing and of the loss of his soul. pg 351
Daily Halacha 13 ShevatThere are several early sources that warn against mixing fish with milk or milk products. Rabbeinu Bachyei writes that doctors believe that eating cheese with fish can lead to all kinds of diseases, and Beis Yosef warns against drinking milk together with eating fish. But almost all of the latter poskim discount this danger and some go so far as to say that the entire issue is based on a copyist error. Others suggest that we follow current medical opinion concerning this question since it is a medical not a halachic issue. Consequently, only those communities who have traditionally banned the eating of fish and milk together should follow their tradition, but it is not a custom that others should adopt.