What might this be.

[GTR]

I've lost 3 to this. Minor redness them 36 hours later it's open wounds and death.

 

[Deinonych]

Looks like septicemia - possibly Vibrio or Pseudomonas. Could also be Uronema. Did this happen in QT or the display tank?

 

[Dmorty217]

Looks to be skin hemorrhage. Caused by slime coat being disrupted and poor water conditions. Vibrio and Pseudomonas are commonly associated with this. Treat with antibiotics... Kanamycin at 50-100mg/L for 7-10 days Nifurpirinol at 1-2mg/L same duration or Neomycin at 65mg/L same duration

 

[GTR]

They were newly imported fish. I'll try the kanamycin. I was just surprised how fast it developed.