Cory With Spot By Rear (Underside)

[CarJamLan]

Hello! I have owned Corydoras for about six months now, and have come across a weird happening: My emerald cory has a medium sized dark spot near his rear, on his underside/side. This is not affecting his behavior at all, and he is still a happy youngster of a cory. I thought that this might be constipation, and after he didn't eat his peas, (Which he typically doesn't) I was going to give him a salt bath, but thought better of it...! Can anyone help me figure out what this is?! I will attach a picture, but its not great...

 

[DoubleDutch]

Had to watch the pic 10 minutes before seeing some kind of fish hahahaha. Try to place a better one.
Be carefull with salt. Don't know if there are other experiences but to my believe Corys and salt are not a good combination. What kind of substrate do you use and what are you feeding them?

 

[CarJamLan]

I use aquarium salt I got from a local aquarium shop. They said that the corys would be ok with it, but didn't specify about baths.. I didn't want to risk it. sorry about the pic, I'll try to get a better one tomorrow. I feed them flakes, algae wafers, and the occasional cucumbers and peas.