keep up the water changes may help
they have a small throat and may have a restriction, if your lucky it may pass
i see that stiff posture in youngsters i have raised when the food is too big
or not being able to digest it
i defrost and wash ffood in a fine net before feeding to tank, helps to remove any impurities
depending on the fish you can make it a treat or feed more regularly
i won't post a pic as most have ladies draped on them
bobber refers to the rear mudguard on a chopper style motorbike being shortened or "bobbed"
they usually have smaller motors in them also
found one
http://img293.imageshack.us/i/bobber7ll4po9.jpg/