Matak--in some cases, yes. Particles below a certain size can get caught in their gills, clogging them and suffocating the fish, while particles above that size can be flushed clean. Usually the duration of the cloudiness is important--a quick exposure isn't that harmfull, but weeks or months can kill. It also varies a great deal with the type of fish. Some fish come from waters that are naturally high in silt and cloud, so they won't even notice a bit of particulate, while something from clear waters will have a fit.
