Onum lake has 25 trout + 75 = <<25+75=100>>100 fish.
Riddle Pond has 1/2 * 100 fish in Onum lake = <<1/2*100=50>>50 fish.
Combined the three bodies of water have 100 fish + 50 fish + 75 fish = <<100+50+75=225>>225 fish.
The average number of fish in the bodies of water is 225 fish / 3 = <<225/3=75>>75 fish.
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