The rationale cited in Ta'amei HaMinhagim regarding showing mercy upon
animals so that HaShem will show mercy upon us is not given with
regard to feeding fish. It is citing a custom of a particular tzadik who
would feed cattle and horses on Rosh HaShana and Yom Kippur for this
reason. Being that there is no halachic problem with feeding domesticated
animals on Shabbos and Yom Tov this would have no bearing on the custom
to throw bread crumbs to the fish.
Lazer
Eliezer C. Abrahamson
176 East 9th St., Lakewood, NJ 08701
(908) 905-6877 e-mail: Abrahamson@juno.com