Question about the tigrinus

[plecoking2010]

When and how do they get the blue cheeks. Start to appear.

 

[thebiggerthebetter]

The metallic sheen appears to show in mature tigs but I cannot pinpoint the size. It seems gradual to me, over many months / years of growing. I hope someone who knows chimes in.

 

[ceejaye23]

Mine is about 10" now. I noticed this blueish sheen when it got to 8". I've been feeding massivore since it was 3". Could be the food?