Do your Homework. Find out all you can about that puffer's species, if you don't already know. Sometimes your LFS will actually know about them. But be sure! (I've had some stores tell me something I know to be wrong, even though they were quite adamant about it.) Find out what water conditions it will need, and more importantly, what conditions it is being kept in. You'll need to know this so you can match the water in your tank at home. Even if the water parameters at the LFS aren't correct for its species, you'll need to make those adjustments gradually at home. Nail down its species. I can't stress this one enough. This is especially true if you're buying one of the spotted varieties. More often than not I see them mislabeled. Find out how long the LFS has had its puffers, and what they've been feeding them. If you don't know about the particular species, ask to put the fish on hold so you can find out. Most reputable LFS's will do this without much fuss.
Examine the puffer. After doing your homework, take a good look at the fish. You can start with the physical exam:
1. Check for Ick. During transport many puffers fall ill with this disease. If it does have Ick, what kind of physical shape is it in? Unless you "rescue" puffers like I do from time to time, you may not be equipped to treat the disease. If you are, just be sure that the puffer is in good enough condition to make it through the treatment. If the puff has Ick, ask the LFS if they are treating it, and if you may purchase it when it's better. Puffers are challenging enough at first without starting with a sickly one. You don't want to have to deal with this in your tank either.
2. Do a quick physical exam. Are there any signs of disease? Are its fins working properly? Puffer's pectoral, anal, and dorsal fins are almost always fluttering. If not, just keep watching, a healthy puffer uses them almost constantly. If its fins are a little ragged, don't be set off. Keeping many puffers together in such a small area can make them even more ornery than they already are. Fin nipping happens, and most of the time this will heal. Just be sure it hasn't acquired an infection as a result. Check its gills. Make sure they aren't clamped. Check the color of the puffer. If you've done your homework, you'll know what it's supposed to look like. If the puffer is a little darker than normal, it's probably ok. Overcrowding or errant water conditions can do that. (e.g. if green or spotted puffers don't have enough salt in their water, they won't have that nice bright green color.) If you're purchasing a puffer that has a white underbelly, check it. This is a great indicator of how stressed the puffer is. If it has a grayish line between its dorsal coloration and belly, it's stressed. This is ok, and normally only temporary. Spots and rings, however, aren't ok. This may indicate some type of disease. (Although sometimes it's simply a matter of salinity for some species.)
3. Take note of swimming patterns. Puffers, in general, aren't very timid fish. If the tank is overcrowded, then the less dominant fish may be hiding, or trying to. This is ok. If the tank isn't crowded, the puffer normally would not be hiding. It shouldn't be lying on the gravel, listless. This is definitely a disease indicator (depending on the species: e.g. congo puffers naturally lie on or in the substrate.). Overall, just ensure yourself that the puffer seems to be swimming normally. You can view a movie of a figure-eight puffer swimming in its tank for comparison.
4. Check its tankmates, if it has any. Puffers are often kept with Cichlids, because of a similar temperament and taste for water conditions. If you want some tankmates for the puffer, here's your proof they can handle each other. I always check the tankmates as carefully as the puffers, since certain diseases are easier to spot in other fish. Additionally, if you see puffers with fish that are nowhere near similar in water parameter, you know that LFS probably doesn't know much about puffers. (I once saw green puffers being kept with Elephant-nose fish!!!! yikes!!!)
5. Watch the transfer from tank to bag. This isn't imperative, but like I've mentioned in previous pages, making your puffer "puff" is rather stressful to the fish. See if you can convince the LFS person to do the transfer underwater. Have them "scoot" the fish into the net or little iso-tank. This will prevent the puffer from taking in air during its puff, lessening the chance of damage and stress.
6. Buy its food right there. No, I don't get a kickback from the LFS. It's just that you should try to encourage your puffer to eat as soon as it gets to its new home. It's much better to start it off with a full belly. Most of the time it will happily accept its favorite foods.
7. Buy some Stresscoat. Nets damage the slime coat of fish. Any new fish should be dosed with some stresscoat, as it helps to restore this. Since the coat is its first defense against infection, it's wise to keep it healthy.
8. Keep your receipt. Find out about the return policy. You should do this with all fish. Hopefully you won't need it, but hey--you never know.
Enjoy your new Puffer!!