It's difficult to say for sure without knowing anything (tank size, exact stock, parameters, wc schedule, diet, etc). He appears to have a white area on his side as well and appears underweight.
My first suggestion is to check the parameters. Moors are particularly sensitive to unhealthy water conditions. Toxins present and/or low ph can cause white areas on a moor as well as induce bottom sitting. Nitrate levels that read 40 (or higher) as well as an improper diet will also cause a fancy to bottom sit and have buoyancy issues.
If you can provide more specific information, we can provide further help!