You have not mentioned what your water parameters are yet?
If you have done "research" you should know, JDs (and other Central Americans, are hard water , high pH species,
and severums and oscars tend to be soft water, low pH species.
Not that they will immediately kick the bucket if parameters aren't perfect,
But if you put oscars and severum in even moderately hard, high pH water, as they age, they tend to get HITH.
Or if you put Central Americans like JDs or others such as Vieja in soft water, they tend to to bloat as they age.
What your tap water parameters are, could have a bearing on what species you should mix together in the same tank,.....or not.
If you have done "research" you should know, JDs (and other Central Americans, are hard water , high pH species,
and severums and oscars tend to be soft water, low pH species.
Not that they will immediately kick the bucket if parameters aren't perfect,
But if you put oscars and severum in even moderately hard, high pH water, as they age, they tend to get HITH.
Or if you put Central Americans like JDs or others such as Vieja in soft water, they tend to to bloat as they age.
What your tap water parameters are, could have a bearing on what species you should mix together in the same tank,.....or not.