Complex sentence: They have very poor eyesight, so detected movement from outside of their habitat can be seen as a threat; if stressed, their first instinct is to flee and such a blind dash can result in injuries in an aquarium environment.
Split into simpler sentences: They have very poor eyesight, so detected movement from outside of their habitat can be seen as a threat. If stressed, their first instinct is to flee; a blind dash can cause injury in an aquarium environment.