I feed my lions ghosties, mollies, and guppies; i have 6 lions with these included in their diets, my oldest lion is 7 years old, I've kept them as long as 11 years with this being their main diet.
If you have the money and time to feed marine fish and shrimp, have at it. If kept properly, fed and enhanced, I don't think you'll find any difference. If you feed marine and don't qt and treat for parasites, good luck. Good luck finding marine shrimp not kept in a system with fish, which means a possibility of carrying disease.
The bad rep of feedng fresh water fare likely comes from feeding gold fish and rosies, which is not a good idea. Ive had tbis debate many times with people who have barely kept a predator alive for a few months, and some that have never kept them at all. On paper it makes sense, but in reality it's just not practical for most.
A qt tank, a holding tank for qt'd fare, and the expense and maintenace to go with it. I spend $80 a month on live foods and really no maintenace to speak of on my feeding tank. That would be close to $250 and the maintenace of 2 marine tanks for all real life purpose would likely make no diffefence.
I've had positive results keeping my dwarf and medium bkdied lions at least supplemented with live feedings. While I've found many not do so well long term on a dead only diet.
