For this article, I am assuming you know enough about basic fish care to be considering which fish you would like to put into your new tank. This is a crucial decision. Do not trust some store employee to tell you which fish you should choose. They most likely know very little. It's up to you to make a wise decision. I am going to list five fish commonly purchased for a first aquarium that are horrible choices. However, store employees constantly sell these fish to unsuspecting customers who will most likely be back in a few weeks to replace their new pets that have gone on to that big fish tank in the sky. I will also list some much better alternatives that will allow you to get started in what can be a very fascinating and rewarding hobby. In determining the best beginner fish, I first wanted to make sure that they were hardy enough to allow for beginner mistakes that are bound to happen. Secondly, I chose fish that could live happily in the common community aquarium that most beginners like to set up. These fish don't require huge tanks or need special care to survive. Hopefully, this lens will guide you in choosing fish that are both appealing and appropriate for your aquarium.
My personal recommendation...
Understanding everything there is to know about fishkeeping is a difficult task. I cannot stress enough the importance of reading magazines, books, and good websites to gain more knowledge about the ever-changing fishkeeping hobby. Tropical Fish Hobbyist is a great magazine to help you grow as a fishkeeper. I have been reading it for over four years, and the information I have gained has been extremely helpful. Every month, a new issue comes in the mail, and they provide great articles, answer questions, and highlight new species. Give Tropical Fish Hobbyist a try. You won't be disappointed!
#5 Worst Beginner Fish: Oscar
The oscar is a common choice for people looking for a large predatory fish. It is a member of the cichlid family known for their big personalities and aggressive nature. Many people enjoy watching their oscar make a meal of the poor feeder fish that swim too close. It's hard to resist the big eyes of a baby oscar begging you to take him home, but they make a poor beginner fish for several reasons. First of all, they require a larger aquarium than most are willing to start with. oscars can grow to be up to eighteen inches in length, and they have a large body mass. The minimum would be a 55 gallon for a single adult oscar, but even that is pushing it. You would have to be meticulous in doing large weekly water changes and have no other fish in the aquarium. Because of it's size and messiness, the oscar really should be kept in 75 gallon tanks or higher.
Also, they are very susceptible to hole-in-the-head disease which can be very difficult to treat. Large sores develop on the head and along the lateral line of the fish that can eventually lead to its death. It is believed to be caused by poor water quality which is common with oscars. They produce a lot of waste, and if the water is not changed regularly, the built-up nitrates can become toxic for the fish. In addition, the feeder fish many people give to their oscars can bring in many diseases to the tank. I really don't ever recommend using feeder fish unless it is absolutely necessary. If you do, you should quarantine the feeder fish in a separate tank to check for diseases before giving them to your oscar or other fish in your main tank.
Lastly, it is very difficult to find compatible fish to keep with oscars. They will eat any fish that they can get into their surprisingly large mouths, so you must keep them with similarly-sized fish. However, oscars can be very territorial and prefer to be left alone. They will beat up on other fish they view as competition, but they also can get picked on by the bigger and more aggressive members of the cichlid family. This means that you need a huge tank to house oscars with any other fish. Most beginners like to have more than one fish in their tank, but it is very difficult to do that with oscars.