Yes - because in freshwater - the chloride cells concentrate the NO2 levels in the blood - it is an active process through the chloride cells - and in saltwater - you have one active process in - through digestive tract and one out - the same chloride cells but in saltwater their function basically is to pump out chlorides but in a nitrite contaminated water - they have to pump out NO2 too (that have been actively pumped in by ion pumps in the digestive tract). If we look at the chloride cells - they may pump equal amount of nitrite but in two different directions if you compare fresh and saltwater. This will demand energy and in the saltwater example decreased ability to withhold osmotic homeostasis. There is reported damage on the gills both in fresh and saltwater. There can be a stress response. There is so many things that says that you should not put in fish in water with high concentration of nitrite even in saltwater.Yes, Lasse but in freshwater fish it is much, much more
This is two orders of magnitude difference.
Sincerely Lasse