Bass are apex predators, but they are also lazy. They have a very fast growth rate, and if the Rosie's get to be difficult for them, they will simply eat the koi/goldfish. You would also need to add other forms of food for them, such as crayfish (they are relatively easy to find and order online in large quantities) to keep them hunting all forms of food, and it will provide more nutrition. You would also need to keep massive quantities of rosies, as the bass would constantly eat them, as they are opportunistic hunters with their prey confined with them.
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