Thank You Message In Ceremony Program What Is The Purpose Of Putting A Fish In Before Planting A Tree?

What is the purpose of putting a fish in before planting a tree? - thank you message in ceremony program

Let's Have a tree planting ceremony and had read somewhere that you are a fish in the hole before the tree (instead of something else fertilizer? Food tree? Can throw). If this does not push the tree, then there is a certain kind of fish should be properly treated? I believe that children Help us to plant the tree, you can have fun with this part - either something else in the hole before planting, such as news or time capsule. What do you think the trees would be fun for kids? Thanks