You know you are a fish keeper when you call your local zoo aquarium and ask the curator what to feed your newly hatched baby octopus and he asks if he can come to your house and see them.
You know you are a fish keeper when you have so many tanks that you apply for a job as the keeper of the fort worth zoo aquarium marine section and you get the job even though they don't know anything about you other than what you tell them, no job experience, no references to give them, just what you know from your own personal experience as an avid hobbyist.