It's not essential but making an intro post helps get the new account working. A lot of people join the forum and their first post is in the help/ emergency section. Sometimes it takes a day or more for the moderators to clear the post and activate the account. By then it's often too late for the fish.
By making a simple intro post, you get the account activated and then if you have problems with the fish further down the track, you can get help sooner.