My fishes never leave anything now , many factors i guess , its environment , if too many fishes or smaller pond or warmer climate , its also habit or they learnt from each other ,if one or 2 fishes started in earlier days then all will learn and becomes habit , i had plants in start for few years and they were fine , one morning a fish thought we should try them they look tasty lol after that others followed them and now they wont leave anything , i tried even very stiff large water lily , they ate it too . You can make a portion with barrier of net or from rocks and stuff where bigger fishes cant enter , or go for above water plants , i have them , they do same job . I dont think feeding them alot will solve it , 1st of all ur pond and filter will be over burdened with that much feeding and im sure u can never fill there bellies , if they have developed habbit they will still destroy plants .