Perhaps an evolutionary trait? One of my shubies is shaped much differently then the rest. The main 3 are growing fast and distributing the weight evenly across their bodies in a nice, mostly oval pattern. My jawy shubie, Zon, the 4th fish of the tank seems to actually chew food instead of just sucking on it like the rest. He/she takes tiny bites and takes a long time eating food, therefor getting much less food then the others. Zon was once the 2nd biggest fish and now after a few months he/she is the smallest shubie.
I've also noticed that Zon's weight isn't distributing as nicely, the butt/lower back before the tail is narrow and pinched looking, while the head has a defined neck and skull shape. Zon is skinnier but not for lack of trying to eat, he's out there getting food and chewing it but since it takes so long to consume he get's less in general.
I'm thinking of getting some nutrients that dissolves in the water and absorbed in their scales. Has anyone ever tried that? I don't know what brands to look for. Also a note of concern, the other fish getting enormous while Zon catches up to a healthy weight with that method.
They were all born in Spring 2011 and measure between 3-5" in length including tail.