It can be said that in this comparison I did not mention the cost of the pet fish and pet dog. In my opinion, it would not be correct, because there are a lot of kinds of fish and dogs (big, small, fashionable and so on). In this essay I have taken as an example the middle size of the fish and a dog as an example.
To sum it up, I would like to say that if your goal is just buy a friend, then the choice is broad enough. You need only to think about what kind of pet you prefer. If you love to be accompanied by a reliable and loyal creature, and at any moment, ready to rush, to execute your command, then you should take the dog. If you are irritated by the fact that wherever you look, everywhere you see the eyes full of love and devotion, and you prefer restraint in showing love and also love peace, along with the quiet independent nature, then take the fish.