Can the dragon goby live with out salt in the water?

Question

and why do pets stores say they can?

Answer 1

They can, but long term, this leads to very weak, disease-suscpetible fish.  Pet stores will say they are fine in freshwater because it's easier than convincing people they need to get marine salt.  If you do try to keep it in freshwater, the lack of dissolved minerals will lead to constant osmotic stress and respiratory issues.

Please check out this article: http://www.thefishworld.co.uk/id184.htm