i'm pretty sure that the fish is both "fat" and VERY gravid. Loaches get esp. fat when breeding and i'm pretty sure that marge is an extreme example. The way I understand it they have super expansive eggs.
That picture dowsnt do Marge justice...The fact that Ema Turner has raised her to her current size is a testament to her great care for her loaches. Most of us don't keep Clowns for that long, much less considering their growth rate. Marge may be a bit fat, but my bet is she extremely gravid. All clowns lose their color as they grow...here is a vid of Ema's tank, including marge...you get a better idea and appreciation for well taken care of clowns