Which fish is most commonly mistreated?

[Silly me]

every second fishkeepers got a bala shark or two in there 10G

I found Bala shark to be more comman than Goldfish

 

[noelberg]

Glass tetras.

I might have seen them without dye once. Talk about the most frequently dyed fish. While I do deplore the state that bettas and feeders are kept in stores, I detest injections and dips even more. Feeders and bettas can be given better homes, but you can never take away the fact that a glass tetra or any other dyed fish was injected/dipped. Furthermore, these fish usually end up in the hands of inexperienced fishkeepers because of their color and because the knowledgable aquarists know that they are dyed.

 

[drobbins27]

After seeing a full grown Pacu, then seeing them as juvenilles for sale in Wal-Mart....they should probably be on the list too 

they are

hee hee, I didn't even notice it was a poll

 

[DiXoN]

if your talking about mistreated by there owners then it will be goldfish (kept in a bowl with no filtration and hardly ever cleaned)
then piranha as there bought for the wrong reasons kept in too small a tank and generally abused.
dixon