Mixaill studio presents a good solution for your games, VR projects and simulators - River fish
You can use this models for your simulator games. All models low poly and have two object: fish body and fin. It good for collider.
Pack includes 25 fish. (on average 2,000 triangles each fish)
All fish have animation - Swim (includes in Perch)
If you have any questions, write me: firstname.lastname@example.org