Yoyo Loach Size Differences

[Channti]

I've got a group of about 8 yoyo loaches (my best estimate, never see them all at the same time for a 100% correct count).  All were purchased over the same two month time frame.  All of them came from the same pet store, same store supplier, and were kept in the same tanks from LFS to my house.  They've all been fed a diet of blanched zuchinni (meant for the Pleco, but they help themselves), Shrimp Pellets, Algae Tabs, and Flake.  At time of purchase, they were all scrawny little things less than 2" long.
 
FastForward, Year and a half after purchase:
 
Despite all of this, I have some loaches that are up on 3+" with stocky bodies, while others are still barely 2" and skinny.  Is this normal?  One of them is so scrawny that I was certain he wasn't eating, but he's continued to live for four months, and shows no sign of illness, so I assume his scrawny-ness in my eyes is still healthy as he MUST be eating.  Is it normal for there to be that much variance in a group of loaches?

 

[Baccus]

From what I have read this is pretty common with the likes of clown loaches, it could be just that the other larger loaches are putting out more growth inhibiting hormones and the scrawny guy is getting a constant dose. The other thing to consider is the tank size and availble floor space in the tank, could the scrawny guy be getting stunted from over  crowding?

 

[BigFish01]

I had a clown loach do the same thing. He survived almost 3 years before passing, his brothers were three times his size. (or sisters really who knows) it was always out and about, first one for food, just never grew. then over night it took a turn for the worst and passed that day. I think it was "skinny disease, or wasting disease" which is caused by a parasite in their system that stops them from growing, but I never figured it out. All my polka dots and clowns now seem to be growing great. Hope someone can shed a little more light on this subject for you!

 

[Channti]

The tank itself is 46 gallons, and there's plenty of territory in the tank between the driftwood and plants.  Overcrowding doesn't seem to be an issue here; the only bottom dwellers in the tank are the loaches and the Pleco.  Other inhabitants are an Angel fish and some serpae tetras.
 
If it was an overcrowding issue, I would assume that these size differences would be pronounced throughout the whole group, not just a couple individuals.

 

[Baccus]

I  am sorry if it seemed I was saying your tank was over crowded but there was no information on the tank size or other inhabitants apart from the pleco.
 
It could be a case of something like an internal parasite that is stunting its growth or something like I already said where the other fish are releasing growth inhibiting hormones which your little guy for what ever reasons is more susceptible too. I have seen this growth inhibiting in action with BN fry, while I have a few hundred fry they will all grow at varying rates, but as soon as I can start removing more of the biggest fry the smaller ones quickly start growing. It gets really noticble once the fry numbers start gettting down to the 30's-20's. In no time at all the smallest fry that had hardly grown will be sellable sizes, once the biggest ones have been removed.
 
It could even be something similar to runt syndrome in almost any animal that has litters of offspring. Maybe the little guy is just a runt.