normally a bacterial infection will start in a certain spot and spread from there like a crawling plant. Parasites can move and crawl and will often place themselves around the body in random places. Like fish lice for example. Parasites imbed themselves under the slime coat of the fish and seem to be more sporadically placed then bacteria. Notice how the sores don't touch one another as if each sore has its own territory. These things look sort of look like they are identical in shape meaning there is more than 1 of whatever this is. Bacteria is not likely to emulate its shape of how it attacks. See how the sores look identical to each other like the same breed of parasite has gone about its business in the same way in each spot. It's like a heap of sores on the fish where something has sort of drilled into it. Like a clan of parasites marking their spot. I just get the feeling this is parasitic due to that. Look at the parasitic worm that attacks human's called ring worm. It plants itself around the body of the human host in no specific spot and they don't usually collide with one another. I'm not saying it definitely is parasitic but it just doesn't look bacterial IMO. But of course I could be wrong. I am not claiming to be correct as I'm not a fish doctor although I read a lot.
Bacterial infections often start in the gills and around the mouth also or directly on top of the back or open wounds. These sores could turn bacterial though as the flesh is exposed and skin is broken opening the fish up to bacteria and viruses and especially fungus as that will latch onto anything slightly not right.
In saying all this, there is a bacteria that could be responsible and that's the bacteria that causes haemorrhagic septicaemia. Lesions, ulcers or sores on the body, reddening at the base of the fins and the vent, loss of appetite and darkening of coloration are all symptoms. That's when the bacteria is internal and is breaking out of the body causing the leisions. The fish needs antibiotics for a long duration.