I have had my turtle/fish setup for almost a year now. here it is... a few months ago...
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I have three 5" koi, two 4" comets, two 6" pacu and one 6" Red eared slider. the happilly live together and have grown well in the year. The turtle did eat 2 plecos that I tried to put in there. One thing that I must stress for such setups is FILTRATION my 55 gallon tank is fitted with a system that is designed for 150 gallon tanks, cycles the water 8 times an hour.
feeding becomes interesting, the turtle is on a diet, and tries to eat the fish food.