Good for you that you have these moments with your son. He will always remember them. I find myself doing that too, but more just with myself, though I have a 12 year old. I have the shrimp, say "Cool, here comes food. . no it's mine . . hey!" etc. etc. I love doing that. Great stress relief.
I remember when my daughter was 3 and we were leaving the library with a huge fish tank by the door, as we left she said, "Have nice day fish". I still remember how cute that was, the way she said that so sincerely to the fish. To this day she is a compassionate kid to both people and animals. Caring about animals is a great place to begin to building empathy.
Lucky child you have - enjoy these days. They do grow up so fast