HEALTH
Please could you assist with recognition of the disease that affected the discus in the attached photograph? When I noticed the problem two days ago, I thought at first the tiny white spot—which looked a bit like a grain of rice—may have been an ich breakout. I quarantined the fish and administered Seachem Paraguard in both the main tank and the hospital tank, just to be on the safe side. But the following morning the spot had gone, replaced by a 2mm hole, and by the next day the hole had progressed to the state in the photo, and the discus was lethargic, laying on its side. It was still alive when the photo was taken—I’d thought it was dead when I netted it as it did not move, but it suddenly gulped for air, so I immediately returned it to the hospital tank, although within a couple of hours it had died.
The main 160-litre tank contains three discus, a bristlenose catfish, three yo-yo loaches and two rainbow sharks. I have double-checked the main tank occupants under a magnifying glass, and all seem well and are eating. Please could you advise?
GLENN WALSH
PETER SAYS: Such a sudden demise in an otherwise seemingly healthy fish does narrow down the likely possible causes. On the picture of the affected discus, we can see a large area of white necrotic skin with a reddish ‘bruised’ border, and in the centre, it looks like the skin layers have eroded completely, resulting in an ulcer that reveals the underlying muscles.
There also appears to be skin erosion and/or scale loss on the upper body near the dorsal fin and there’s an extensive area—particularly over the front half of the body—of translucent/milky skin that might indicate excess mucus production.
My thoughts as to possible causes are:
Bacterial infection, such as caused by Aeromonas or other bacteria that are associated with skin damage and ulceration. Some of these bacteria cause bruising due to their enzymes affecting the skin. However, it would be unusual for a bacterial infection to overwhelm a previously healthy, uninjured fish within just 48 hours. So, if bacteria were to blame then maybe the fish had sustained some injury that allowed the bacteria to infect and overwhelm it so quickly. Also, chronic stress can impair the immune system, making stressed fish more prone to bacterial, and certain other, infections. But if the fish was behaving and eating normally that doesn’t suggest it was badly stressed.
So, that leads to possible injuries. We must consider whether this fish suffered some sort of physical trauma, causing extensive skin damage and ultimate death. Perhaps
