Interesting. What other fish were in this tank? African Tigers?
Another thing I find interesting is that people have really no idea what they are talking about but some how manage to spew out a large reply, or many small ones which are ridiculously incorrect. (delgado, among others)
The "hump" on the head is rather interesting, especially because its mostly normal tissue. Which leads me to believe it was being pushed up by extreme pressure. Next... look at the pictures... the entire body is ballooned. Now, In 1 post you mentioned your other tig, right before he died was ballooned.. and same with the other one which is now getting better. This leads be to beleive it has to do with an intertnal problem. Which is almost always caused by a bacterial infect somewhere in the body.
This is to all you people who suspect its a deficiency in O2 - Explain, in Detail, HOW a the bloat is caused by Lack of O2 and the fact that it happened slowely over time to the other tigs... AND also explain how his OTHER fish are acting perfectly normal.. (if they are African Tigers, than they are a clear sign the water is full of oxygen considering they have excessively fast metabolisms and require alot of O2 aswell.)
Also, the activity level of the Tigrinus should not be overlooked. They dont just lay around, bloat up, and die when they are hungry for Oxygen. You will notice them swim to the surface of the tank and gulp, You will also notice them head for a jetstream.
TIgrinus aswell as Juruense are indeed found in whitewater so delgado, please. do some damn research first. Also, the Amazon does have quite a bit of Oxygen, it is considered the widest river in the world... which means it has the largest surface area of Oxygen exposure to water... AND, the water is moving, in some parts with quite alot of current. Not to mention alot of the tributaries and such are off waterfalls and are moving quite fast with rapids which bring well Oxygenated water directly into the amazon.
The amazon will CLEARLY have more oxygen than any lake, aside from some rather high altitude cold lakes/ponds.
I am not done yet. I would also like to direct my attention to the fact that you cut open the head part, but not the body. Tell me, what was in the stomach? More specifically did you check the airbladder?
Also, the body could very well have bloated up after death. but He clearly says his other LIVING tigs were starting to bloat.
The body its self should also take more time to bloat, unless there was/is already a bacteria infect present in the interior of the body which would enable for a "seeding" process to further quicken the bloat.
IMO- it was a bacterial infection of some sort, and can not be correctly identified unless one were to get their hand dirty...
also, 6000gph? LOL! chances are, you were not lacking O2. but, then again... it could always depend on the bioload of the tank, and method of which the tank is being filtered.
anyways- good luck with the other tigrinus.