Blue gouramis, head depression

Recently I have noticed that all my male blue gouramis have developed a strange depression near their head. This has happened to my male blue gouramis, I have other different gouramis in my tank but none of them have developed this depression.
The water quality is good and all of my fish look healthy and are eating.
I have watched closely the tank for any signs of agression but they all seem peaceful.
Can anybody tell me if this is a disease or something else.
Thanks

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If you bought the blues at the same pet store at about the same time, I would say this is a genetic abnormality, and the blues were of the same family.

Other than that, I have no knowledge of this happening.

These fish were part of a fry that my father was hatching. But strangly enough it started only with one male, and now his siblings have the same condition. I hope this is a genetic defect not a disease. Strangley it is affecting males only. Thanks