Just a weird question

[TheRod]

I have a planted freshwater fish tank with 4 Cory catfish. 2 of them I have had for about 2 or so months now and today I purchased 2 more from petco. Same species and everything. When I compared my 2 females I noticed one of them was not like the other. She was much darker in pigment. I was wondering if this was my fault. Want to make sure she's healthy and living the dream...
Facts:
I have 50/50 lighting 5600k (or around that number)
Food is bottem feeder aqueon tablets
Piece of bogwood
Java moss on carpet and another plant that I forgot the name in the background of one of the pics.. If you know what it's called lemme know

 

[KimmiA]

Hello!

Whoops!I do believe the darker one is a different species of Cory. Was the species you thought you purchased Julii Cory? From your pictures, that's the type of Cory I see, and the darker one is not a Julii but in fact a Sterbai Cory. Sterbai have darker bodies with light colored spots and stripes and the opposite for Julio (lighter bodies with dark spots and stripes)

Cory catfish can shoal together if they are not the same species, however they do prefer if they are all the same kind. Since you just got them recently, consider taking the Sterbai back and replace with another julii Cory, unless if they all seem to be getting along fine.

Hope this helps!

 

[em_witt]

Yes different species of cories will school together. I have 2 peppered. 2green emeralds. And 3 albino. And they all school
All in a 75gallon tank
When one wanders away from the group, it like freaks out to get back!!!

 

[Rivercats]

Cory's usually lighten or darken depending on the substrate. My Julii's are light in color as your new ones when I got them from Pet Smart and after being in our tanks, all of which have black substrate, they all gradually darkened up as yours. The ones in your pic's are all Julii's and in time the new ones will also darken due to your substrate color.

 

[Rivercats]

Sterbai Cory's are easy to tell as they have orange bottom fins like in this pic... Corydoras sterbai (Sterba's Cory) — Seriously Fish. I love my Sterbai because of those fins.