Mono Sebae not eating.

[Gahandi]

i got this mono sebae 2 days ago, and as far as i can tell it hasn't been eating anything i've put in the tank (pellets, vegetables etc) so unless its been eating parts of the weeds or eaten a small feeder fish, its just not eating.
Any help would be appreciated, is it normal for them not to eat often? anything they really enjoy? could it be sick? plz HELP!!!

 

[cogs]

they are a schooling fish i think so maybe add a few more and a little salt that should help

 

[Gahandi]

i might get another 2 or 3 but im leavin the change to brackish for a while, its still small and its in with all my other freshwater --> brackish fish (a red scat and 2 barras XD)

 

[Gahandi]

just an update, im pretty sure its eating now, its gradually started taking more food and i left some lettuce in the tank overnight, most of it was gone the next day so im hopin it was him who ate it and not the scat.