cuz they're raised in unhealthy conditions (copper-loaded water, to prevent mass disease outbreaks), prone to carrying diseases ANYWAY, they're very deficient in thiaminase (some nutrient allegedly important in fish growth), and being a coldwater specie, they're simply not something our tropical giants would consume in the wild. I view them as swimming corpses.
Experience tells me I can stick 20 goldfish in a well-cycled 10g, and 15-18 of them will drop dead for no reason after a week. No ammonia, no nitrites, 90% water change just prior to adding them.
And I'm feeding these nasty things to my preciouses? oh hell no, I'll keep my guys on pellets, ghost shrimp and whatever expensive schooling fish treat I decide to provide them with on occasion.
