If your fish is a herbivore, you can feed them blanched vegetables. Some options include peas, carrots, lettuce, spinach, and zucchini. They can also have small portions of fruit like apples, pairs, and mangos. Goldfish and koi can have the occasional snack of cooked rice or oatmeal. You should not give most ‘human food’ to your fish as it’s not healthy for them.