Mistake

[Featherfin]

some species breed and/or spawn in freshwater, but spend the rest of their lives in brackish or salt.

seemingly good info: http://aqualandpetsplus.com/Oddball,%20Half-Beaks.htm

just curious..apparently they never quite reach 3 inches long..why don't you feel comfortable putting them in your skipper tank? apparently they are good with things like mollies

 

[Featherfin]

maybe you could try fresh with like one tspn salt per gallon, but if they start seeming sick or unhealthy, you could switch to brackish.

 

[mudskippers]

Yea, I agree trying what Featherfin is saying.. id try that out...