Large light spot on petricola catfish

[FinnedFriendBeginner]

I have 3 petricola catfish in a 20G tank. The tank is setup for almost 4 months now. Today I noticed a prominent discoloration near the pectoral fin on one of the catfish. The discoloration is seen on both sides. The fish is active, is eating food currently and is swimming well. 

Upon closer inspection, I see another catfish having the same symptoms but on a much lighter color. 

Has anyone seen such a symptom? Could this be aggression between the two?

 

Water parameters: 20 nitrate, 0 nitrite, 0 ammonia, KH 40,GH 120, ph 6.8, temp 78

[Colu]

It looks like an injury the fact it has white  on both sides and another catfish is getting the  same patches i would suspect a bacterial infection I would do a course of kanaplex or maracyn2 which every one is more readily available you could quarantine any fish showing symptoms and treat if you can catch them or the treat the main tank @FinnedFriendBeginner

Edited June 11 by Colu

[FinnedFriendBeginner]

@Colu Thanks for the reply. Looks like the marks on both fish have disappeared in the morning. Can it be an allergic reaction to the food,given the quick disappearance?

[Colu]

On 6/12/2024 at 3:35 AM, FinnedFriendBeginner said:

@Colu Thanks for the reply. Looks like the marks on both fish have disappeared in the morning. Can it be an allergic reaction to the food,given the quick disappearance?

It could be stress or possibly spawning  behaviour with the white patches given how quickly they disappeared I don't have any experience with petricola catfish what are your water parameters as petricola like hard water with a pH from 7.5-8.5 

Edited June 13 by Colu