Gourami anatomy and illness

I have had several fish which have died inexplicably. The Blue Dwarf Gouramis have out lived them (perhaps labarynth organ).

The fish have died panting for air and have scratched their scales off to the immediate rear of the bottom quarter of the gill.

Now, I am not asking for a diagnosis. I have a guess regarding the illness. I desparately need gourami anatomy in order to reach a conclusion about the illness.

The fish had to be dissected in spite of my care for my favorite fish. I really believe that the illness is endemic to the tank.

Thank You to Anyone Who can Point me to a Resource. A vet is unnecessary, I have ample experience disecting other things that walk and crawl and identifying disorders. Just lack experience in fish.

Sincerely,

William J. Mitlyng

Environmental details regarding Gourami

In response to OrionGirl,

Dead Fish: two Mollies, four dwarf blue gouramies, two red swordtails, one small orange tetra (sorry name escapes me), six hatchet fish and two Gyrinocheillus(sp?).

Water quality: Ph 6.6, Ammonia 0.25 ppm (mg/L), Nitrite .50 ppm (mg/L), no current nitrate levels but changed 50% water two weeks ago. Specific gravity 1.04, and temperature a constant 78F. Aquarium is well planted. No radical changes have happened to the aquarium in over a month before the last water change. Change water every 4 - 6 weeks with distilled water. Small amounts of marine salt (4 tsp) in a 29 Gallon aquarium to keep the water soft and provide some critical minerals.

The Gouramies were transferred from the tank with the Mollies and Swordtails. The Tetra died in the new aquarium. Two gyrinocheillus (Chinese Algae Eater?).

As I noted, the fish showed a slightly bloated look (dropsy?). I reduced the volume of food over the past two weeks.

One Dwarf Blue Gouramy, two Paradise Fish, two Kribs, and one orange tetra remain in the aquarium.

I attributed the death of two of the Gouramies to the quality of the water in the old aquarium. I attributed the two deaths in the new aquarium to stress. The tetra(?) and the death of six hatchet fish to aggression by gouramies. The dead fish were missing their eyes. As I understand it, this can come from colliding with the cover of the aquarium.

All of this takes place over 14+ weeks.

My interest in the anatomy Belontiidae comes from a dissection I performed this morning. The bloated appearence came from a large red semi-spherical organ. It was devoid of contents and tough compared with the gut. The slime coating was present, the eyes were neither sunken nor projecting. No scales were missing at this time. The fins were intact. The color was unchanged with no spots of any kind. The gills looked atrophied.

I appreciate further information on the problem at hand.