although this is true, its hard to spot on juvies. the best way is by looking at the spots (as described) or by looking at the colour of the yellow. the small spot (L081) is actually a very pale yellow generally in comparison to the other two (L018, L085, L177), and the large spot (L177) is usually a really vibrant colour in comparison.
NB, that L085 is the adult version of L018, and is in fact the EXACT same pleco, from the same place and scientifically speaking. They usually go a paler colour (the black to a more brown) when older though, which is the reason for aqualog having it as 2 different spp. when they were unidentified.
The colour thing is really useful, and unless the fish is unhealthy, the yellowness, should not disappear much due to stress at all (its the base colour that changes). however, if you dont have the others to compare too, your a bit stuck. heres pics of 3 juvies, and it is quite obvious.
