My turtle does the same thing- she gorges on most of them and saves one for entertainment and eats it a few days later. I've come to accept this as her inability to "budget" her food

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I tried to buy her extra fish in case her turtle sitter forgets one day, but sadly, her reserves are gone before I even pack to leave...
So in short, I just buy a dozen or so every few weeks for her entertainment and leave it at that, because I don't think she has the sense to realize that she doesn't need to be such a glutton.