fo sure no dobt, count on it.
the only reason that they return to FW is to lay eggs, jiz, and die.
that wont be happenin in your tank, which is too small in the first place.
(or you can do what i do and assure they will have a home when your tank is no longer comfortable. get them small watch them grow, and let them go... to a bigger tank)
i read about monos in a species book at my lfs and the library. better info than the net.
and you do realize that those "sharks" are like most cat fish. they get huge, and eat like nothin else. 3 of those will eat a 22 dollar brick of krill in one sitting once they get much larger that 8''.
here is my suggestion;
black sand and a whole lot of lace rock.
get 100 lil fish like mollies, fancy, guppies, bumblebee gobies etc.
then get a brackish moray.
hose fish would stoink non stop, so your fry could feed the moray. also, ghost shrimp will tolorate brackish water as well.
so imagine a big *** tank with all sorts of schools of little colorful fish, and a bad *** moray chillin with a belly full.