[JH]

I have I have a 40 gal semi-reef aquarium (LR, crustacea and fish).
I have two puffers that I have had for about 2 years or maybe even longer.
One is arothron nigropunctatus, or dog face puffer, he is healthy as can be.
I have a problem with the other one: it's a fingerprint toby, I cannot recall the scientific name right away.
The fish was fine then all of the sudden it got really weird and skinny as of yesterday, I mean that thing looks like a tang rather than a puffer, the stomach is pinched and it has a weird looking growth on the head, looks like a colliflower disease, but it might be an abrasion of some sort. Another thing, the stomach part has 3 purple veins visible.
I have no idea what is going on, as of today I started treating the tank with MelaFix (for some reason every time I try to put either of the fish in the QT they get even worse, I guess it's stress) and I have always supplemented the diet with Selcon. The fish in question still eats, although not as much as it used to.
All the tank parematers are fine, I am going to do an extra waterchange today to make sure and I feed them the following things: squid, fish, octopus, shrimp, crab meat (all frozen and them thawed and soaked in Selcon) and verious seaweeds.
Does anyone know what this possibly could be and how to treat it? I really don't want to lose this fish.
Thank you so much,
Jules

[Rin]

When I hear the part about being able to see the veins I think Marine Septicemia (sp?) which is possible given the possible abrasion and sudden weight loss. But I really have no bussiness commenting on this given my lack of expertise.

I'd very strongly recommend getting a picture and posting it on Fish Disease Forum over at Reef Central. They have a good bunch with lots of experience.

Good luck.