That was the biggest load of psychobabble I've ever seen. It was from the New York Times which explains a lot. The vast majority of any fish ailments, including lethargy, are directly related to water quality. Having a bunch of "scientists" sticking their lower jaws out and blabbering about the mental state of tropical fish is a joke.
How many times have you seen someone say, "My water parameters are perfect, but my fish are dying." No, your water parameters are not perfect, so don't blow off the possibility when it's a 90% that's exactly what your problem is.
I did get a huge chuckle out the scientist who put drugs in the water and then waxed eloquent about the psychological effects of the "depression" medication when the fish started acting like it was on drugs.