This is a relatively short topic, but an important one nonetheless.

We've all been to a pet store (I hope), and seen the cute little oddballs swimming around.
Then there is temptation, to buy on impulse, or to resist.

What you should do, if you know nothing about the fish in question:
Resist the urge! Ask them to hold the fish, then go home and research it! The fish may be very compatible with your current setups, or you could be in great relief that you hadn't bought a potential monster.

Some general sizes for common oddballs:
Arowana: over 2', be safe, and avoid these unless you have a 6' tank ;)

Bichirs: Anywhere from a foot to over 3 feet (I've seen Congo bichirs for very low prices!) Smaller bichirs will be fine in a 4' tank, but do your research anyway!

Puffers: Don't buy these on impulse, they either get really big, need brackish conditions, or need a species tank (Most will). You need to be prepared to house a puffer.

Gobies/gudgeons: Again, don't buy these on impulse unless you know what they are and what they need. Many species of gobidae are brackish, some get to be extremely large, and there are only a few that you will encounter that can easily fit in to a community tank.

There are also fish that may stay small, but will drive you crazy trying to feed them. Leaf fish, for example, grow to four inches, can be kept in a ten gallon, and a fairly peaceful. Great fish, right? Nope. Leaf fish will ONLY EAT LIVE FOOD food, you can't change them, and they WILL die of starvation if you deprive them of live fish, worms, or brine shrimp. Live fish are the best food for them however ;)


Those are just some very vague guidelines to go by, and they should really be followed if you want to purchase any fish.

Research first, no regrets later ;)