Dwarf corydora not growing

I have 3 in the same tank from the same date. 1 is quite large, 1 is medium and the other still looks like a baby? The small one is healthy and seems happy and I ensure all 3 get food direct to them, so why is this one simply not growing? Any help appreciated

They are in a heated, planted community tank with neon tetras and shrimps and snails. Also has Co2 system. Regular maintenance and water changes etc. Been in same tank together last 6 months

The males stay small. That's a female in front and a male behind. I can't tell with the 3rd one.

GaryE said:

The males stay small. That's a female in front and a male behind. I can't tell with the 3rd one.

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Never knew that! So that's as big as he will get?

It could be sexes (males & females) or intestinal worms, gill flukes or it doesn't get as much food as the other two.