Points to be made -
The Oscar may not, in fact, be stunted. Many Oscars are genetically predisposed to small sizes, some as small as 8". There's no way to say that he wasn't the perfect Oscar for a smaller tank to begin with. Photos will tell the tale.
Stunted creatures do not necessarily live shorter lives. They may be predisposed to a multitude of metabolic issues and deformities, and these ailments may do them in early. But smaller creatures, if not unduly stressed (OMG, the variables in this concept!!!), even if made small through malnutrition or overpopulation, spend LESS energy on tissue growth, require FEWER enzymatic activities for maintenance of body mass and digestion, suffer less cardiac stress (assuming the heart escaped the hazards of the stunting process) and outlive their fully developed counterparts --- the point is: Depending on HOW the fish was stunted, its lifespan (though not overall health) may be shortened, not affected at all, and even lengthened! Should anybody ever think they can stunt a fish on purpose without disastrous results? NO! Never mistreat an animal. Common sense should tell you that. The problem is that we can't ignore all of the examples of slightly stunted critters doing otherwise fine. And 10-12 inches isn't a whole lot of stunting for an O. Unless this thing is just a giant pair of eyeballs with a caudal fin...
Many fish survive IN SPITE of how they are treated. Some creatures are hardy beyond reason. You know how LD50 means half the population died at that exposure/dosage? Well, guess what? There will be a few at the extreme top. The LD90 (accurate usage of term?) population that is atypical for the species or population. This Oscar might have been born to thrive, to deny the elements and push on while the others around him dropped like flies in the face of pollution and stress.
