Buying fishes: a few tips

"A knowledgable salesperson will be glad to help you with your fish purchases," reads an introductory aquarium book I have here at home. "Yikes! ...and equally so will an ignorant salesperson, especially a confidant know-it-all salesperson with an authoritative manner," adds the Skeptical Aquarist. (Sounds like me, come to think of it, so maintain your skeptical reserve!) Caveat emptor! Let the buyer beware!
 
Here are a few tips about buying fishes that will save you headaches from the start:

• 1. Be prepared. Take a shopping list — or keep an on-going, dog-eared list all wadded up in your wallet. Have a cycled Quarantine tank already waiting (but don't quarantine incompatible fishes together). Take a large wide-mouthed screw-top plastic jar if you're buying fishes with spines that tend to puncture travelling bags. Avoid "point-of-purchase" impulses: know your fish before you buy. This often means putting down a deposit, which could always be re-applied to other goods if some research changes your mind, and making a second trip. Don't snap up a couple of new fishes just before you leave for the weekend. 
• 2. Avoid fish with white spots, cottony tufts, fin or tail erosion, dull or bleached-out areas of skin, a clouded or swollen eye, bloody streaks in fins, lumps or hollows in the musculature, lesions, or waxy whitish areas that should be transparent. Pass over fish with protruding scales or flared gills, or fish that are exuding stringy feces with clear or mucusy sections in them. Eschew fish with bloated or hollow bellies. Inspected head-on, your fish should be perfectly symmetrical. Over-large eyes betoken a stunted individual. 
• 3. Buy only from a healthy tank. Don't merely buy a healthy-looking individual from a tank where other fish are listless or infected. 
• 4. Know what a healthy and characteristic example of that species should look like. Look also for characteristic behavior. Bold, active fish should be active. Do they notice your waggled finger? Shy fish may be hiding, but stressed or sick fish will be crammed behind the heater, etc. A fish that is respiring heavily is stressed. 
• 5. Don't "rescue" fish. Retail marketers know that people buy bettas from cramped little jars in preference to bettas kept singly with other fish in 10-gallon tanks. "Rescues" reward and reinforce the very marketing situation you'd like to change, like those well-intentioned church groups that "buy the freedom" of human slaves at markets in Sudan, thereby establishing a going market price. 
• 6. The healthy fish you just bought have been exposed to bacterial infections and parasites. They may be subclinical carriers of infection. Wild-caught and pond-raised fishes always have some light parasite load, which may explode in cramped quarters. Quarantine all new fish, no matter how deeply and sincerely you respect the LFS they've come from. (You might cut corners in a quarantine when you accept fish from an aquarist you know.)

 
Shawn Prescott's article "Buying a better fish" has further pointers in judging the quality of a local fish store that is new to you. Look about you: a badly-run shop is unlikely to offer you good fishes.