Hey Vic, what kind of open wound is it?
(Link is not visible to guests. Please register to view.
has this about wounds
Definition Red sores are best diagnosed by knowing the fish's history. If the fish has suffered trauma the red sores are actual wounds, but if the sores slowly appear they are likely caused by bacteria and are developing ulcers. Redness in the mouth area is probably flex.
Causes and Treatment
Red sores on the body are often signs of a bacterial infection and ulcers. The bacteria that causes these sores is often Aeromonas hydrophila. This type of infection is often secondary to fluke infestation, so we recommend treating for flukes as well as addressing the sores directly. It is important to isolate the fish in a hospital tank. You can treat topically as explained here and combine this treatment with feeding of medicated food. Medi-Gold and MediKoi are the best choices for treating this kind of infection. If there is a white center developing, it is clearly infected and may be ulcerating. The fish may need to be injected with an antibiotic, or if that is not possible treated in a bath of Tricide Neo (sometimes sold as Neocide 3).This is a serious illness, but treatable, so please post in our forum so we can help you more specifically.
Cuts and Scrapes If the sore is the result of an injury, the best thing to do is to keep the water clean and feed good food so that the fish will nicely recover on his own. The sore can be swabbed one time with Iodine or 3% hydrogen peroxide. Additional swabs will kill the new, healthy cells growing in. If the fish has suffered some trauma and is bleeding, pressure can be applied to the wound to stop the bleeding. You may want to sedate the fish first as described here.
Maybe just have a think, look around the tank if it was possible for the cichlid to have caught itself somewhere or if another fish is the culprit?