my snowflake moray appears to have a tumour

[whatcaneyedo]

I just snapped these pictures after feeding my snowflake moray eel and lion this evening. For the past couple of weeks the moray has exhibited some kind of swelling in its 'neck' (dorsal?) region just behind its head on its left side.

I've had this eel for about 8 years, its appetite and activeness hasn't changed. Throughout all of its captive life I've fed it silversides or krill every second day with the occasional raw grocery store clam or mussel for some variety. On a few rare occasions I've also fed it a carpet surfing wrasse.

I suppose it could have hurt itself somehow and now this is a little bit of swelling that will hopefully heal and go away. However in all of the years that I've had it I haven't seen anything quite like this. So I'm concerned that it could have a tumour... either way I doubt there is anything that I can do about it aside from document my observations here.

Has anyone else heard of or seen anything like this before? The only changes I've made in recent months are I've used a little bit of Reefer's Best salt in addition to IO in my water changes. And I thought I ran out of Hikari Krill so I bought and fed Pro Salt Krill a few times. However the swelling appeared slightly before the change in Krill.

Temperature 77F
Salinity 1.025
Alkalinity 8dkh
Ca 450ppm
Mg 1400ppm
pH 7.9
NO3 and PO4 haven't been detectable in years.