The reason is that Turtles can't afford too much energy to get a meal. I used to just get a few free dead feeders and offer 1 or 2 and freeze the rest. I don't like to cripple a healthy fish.
You can also offer your Turtle it's fish ( dead or alive ) in a shallow small container. Put Turtle in with fish so he can actually catch the fish. Don't overstock a Turtle tank, it just adds to the Ammonia !
I had a single Goldfish living with my Mud Turtle. He was getting larger, Turtle never tried to catch him. People said they were friends. During a big water change the fish panicked and got disoriented. His Turtle " buddy" chomped him.
I also fed Worms, Crickets and other foods. Including Veggies and greens.
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