Whats Wrong With My Dragon Goby?

ok so here we have picks of fatty and skinny.
they were both purchased on the same day (afew months ago now)
and both looked very similar in size to one n other...
but now as you can see one is growing nicely and getting fat, while the other has become rather skinny looking
 
i search the tank every day and make sure i drop food at both of their locations to make sure they are both eating
(and watched them eat too) so i cant understand why skinny isnt putting any weight on.
 
today hes acting rather unusual than normal.
as in hes been out of hiding all day (normally hides till lights out)
and just lays their while the hoplo cats nudge under him when scavaging (normally he would shoot of back into hiding)
and has made no attempt to grab any food.
i even fished him out the tank and placed a couple of bloodworms in his mouth, which he spat backout
 
hes now in the nursing tank but still not taking his food
 
any help and/or advice would be greatly appreciated. thanx

I have never kept these guys but by the sounds of it he may have a parasite load and an infection. I wish I knew more about this species of fish and what they are prone to also what medications are safe to use on them.
 
The only other thing I can think of is what have you been feeding them? Could something have got lodged in its throat or intestines that turned it off the food to begin with?

ah sorry for the delay in replying and thanks for your response. sadly he passed away two days afteri posted.
 
he was being feed on blood worm, tetra prima which is a complete food for discus and other mid-water and bottom-feeding fish,
and anything else he managed to scavinge from the  bottom of the tank,which would have been any fallen tropical fish flakes
or agae wafers(which i always break in half before dropping them in the tank)
 
but he would often lay by the drift wood stretching his mouth wide open as if he were yawning. never saw anything in there
 
they are quite fun to watch when they do come out of hiding, you should get one