It's the angle that he is curved in the picture that made him look so thin he was actualy quite well fed (not overfed or underfed), i introduced him and a watchman goby as the first fish in my new tak, also along with some snails. One of the snails died and i failed to take him out for a day. Im thinking maybe a spike in something killed him, however the goby was unaffected. I never saw him eat however while the hermits and brittle star (hitchiker) and goby ate.