Hi.. Fissures in the anus occur mainly due to constipation.. If you can avoid constipations you can prevent it from happening.. Once in a while taking non vegetarian diet will not affect you if you can include plenty of fibres in your diet.. For the time being till your fissure heal, you need to restrain from chicken and fish. And for long term management, include plenty of fibres in your diet and also increase your water consumption...