McDonald's Co. (Japan) chose fish Monday and Yoshinoya D&C Co. went for pork as new alternative dishes.
For Yoshinoya, the new item comes after the firm ran out of beef for its mainstay "gyudon" seasoned beef on rice dish, following Japan's ban on U.S. beef and a switch to chicken didn't work out because of the avian flu outbreak.
McDonald's, whose burgers are made from Australian beef, introduced Fish McDippers -- six pieces of fried whitefish served with either sweet chili or tartar sauce -- for 220 yen.
Yoshinoya launched bowls of "butadon" pork and rice for 320 yen. Its "buta-kimchidon," or pork-on-rice with kimchi, will be sold for 370 yen, company officials said.
Following the discovery of the first case of mad cow disease in the U.S. in December, fast-food chains that use a lot of American beef were forced to diversify their menus.