Most turtles get accustomed to the fish and don't bother chasing them actively, although just about any turtle will eat a dead fish that it finds. There's always the exception to the rule...that one turtle who spends all day every day scheming and plotting to catch a fish...but that's not common. I have an adult-sized Musk Turtle which has lived since it was a hatchling with fish...Guppies, Medakas, Rosy Reds, Porthole Livebearers, Corydoras, though not all at the same time...and I have never seen it strike at a live fish. Many years ago I had an indoor pond/tank with several large Red-ears, Diamondbacks, Cooters, etc. together with goldfish and never lost a fish to them...but that was a continuous flow-through system and it still wasn't ideal in terms of water conditions.
Having said that, the fish were added just to add a bit of spark and movement to the tank; I would never introduce something special that I really, really wanted...like your Ornate Bichir.
Reading through this thread, I see both 100 and 200 gallon tanks mentioned. If it's 100 gallons, you are already overstocked with two large Red-ears. If 200, and if you have efficient filtration, and if you are committed to massive and frequent water changes, you could probably get away with a school of smallish, hardy, preferably fast-moving fish like Danios or similar. Guppies would probably work. But if you don't want to make this a fish torture chamber, you'd better be ready to change water a lot. To be clear, I'm not referring to 20% weekly changes; think more along the lines of 100% at least once a week.
And, since it sounds like this will happen no matter how many people suggest that it shouldn't...get into the routine of feeding the turtles in a separate container. Use a Rubbermaid-type bin, fill it with a few inches of water of the proper temperature, and place the turtles into it for feeding. One at a time would be better. Leave each turtle in the bin long enough for it to finish eating and also to produce the massive post-meal poop that usually follows, before returning it to its tank. If your Red-ears are adults they would be fine with twice-weekly feedings, and doing it this way goes a long way towards keeping the tank clean...or at least less polluted.
Just be aware that keeping fish with turtles will never be ideal for the fish, no matter how much money you spend or how much effort you put into water changes.