There is an opinion in Gemorah Pesachim 114b – Chezkiyah says for the Seder plate one could use fish. My wife is vegetarion and so we only have milchiks at home. Getting meat for the seder plate is always difficult as we do not have any meat keilim to prepare the meat. Also our meal is always milchik causing a kashrus concern. Can we rely on this opinion of Chezkiyah and have a piece of fish and a roasted egg for our Seder plate?
There is a special reason for placing a zeroa on the Seder Plate, and you should try to keep this custom, even though I understand there is some inconvenience (we don’t follow the da’as yachid of using fish).
There is no need of course to eat the zeroa, and no special kashrus concern.
See Orach Chaim 473:4, and Mishnah Berurah 32.