I'm sure someone will go into more detail about this. You can't compare the diet of a wild Dovii to a captive one. Sure a portion of their diet contains other fish but these "feeders" also contain none of the natural diet that their wild counterparts would. This is where a lot of the nutrition comes from. Even species such as yours benefit from the greenery that their prey consume. It is far better for our pets to be fed a high quality pellet as a staple.