Yes when you deep fry fish in cooking oil the deep fried fish when fully cooked and ready to eat will float to the top of the cooking oil.
Having fried fish float to the top when deep frying it is a good way to know when fish is done.
You can also tell when fish is done when it becomes flaky and it's no longer translucent in color.
No matter how you cook the fish you can tell when the fish is fully cooked and ready to serve or eat when the fish flakes easily and is no longer translucent
If your fish is floating after deep frying it then the fish is fully cooked and ready to eat.