I decided to follow through and have the necropsy done on those two Odessa Barbs. The short of it is that the vet is highly confident they were infected with Mycobacterium
(Fish TB). In my explanations below, I'll stick to the prior naming convention of '1' for the fish with all the weight loss and '2' for the one who had Dropsy symptoms.
After discussing the results, we decided to go ahead and send off the samples to a histopathology lab to confirm that it was Mycobacterium
and not something else (according to the vet, there are very few other things that could cause these results under the microscope). Doing the histopathology will have the added benefit of seeing if there were any other bacterial or parasitical infections going on that we didn't see (including identifying the one nematode parasite he found).
At this point, I should put the disclaimer that all the pictures you're about to see were taken by and are the property of Dr. Brian Palmeiro and are posted with his permission and encouragement. The explanations, however, are based off my recollections of what he told me and any errors can thus be attributed to me (I welcome correction of any such errors, but if you're harsh in doing so, I'm liable to respond with an inverse-McCoy: "Dammit Jim, I'm a pilot, not a veterinarian!").
I'm including more slides than are directly relevant to this diagnosis, mainly because I thought they were really interesting and I thought you guys might appreciate them (but at the same time I apologize for the extra-length post as a result).
How about we start with the only bright spot of the day? Here is a section of 2's gills:
Have you ever heard how the ammonia in an uncycled tank can burn the gills of the occupants? The result of that is a thick coating that develops around the tissue and reduces the gill's ability to exchange gases, which is what makes this image notable: there's no such coating. Dr. Palmeiro said that these are the healthiest gills he's observed in a very long time and that it's evidence that my water quality is very high.
Now, onto the bad news, here's a section of 2's kidney:
The large dark masses are the granulomas that are a characteristic fingerprint of TB. As you can tell, there are a significant number of them. In case you're like me and first noticed the branched dark-spots with hard edges instead of the more rounded granulomas, those are apparently pigment centers and are normal.
Here's another section of 2's kidneys:
Maybe it would be more accurate to say that this is a picture of where 2's kidneys should
be. The granulomas have taken over to such an extent that 2 actually had almost no functioning kidney tissue left. This, not a secondary infection, is the reason for the dropsy: because the kidney wasn't functioning to expel fluid, it was building up within his body and causing the bloat I'd been observing (you know, I didn't know that fish pee. It makes sense, I just never stopped to think about it before!).
1's kidneys weren't as extensively damaged, so he was still able to expel that fluid and avoid the bloating. Before today, if you'd asked me which of the two was in worse shape, I'd have guessed 1 over 2 nine times out of ten. Shows what I know...
In case you were wondering, here's a not-so-bad section of kidney to compare to (this is from fish '1'):
Note: the less-brown background color of this one is evidence of what I was saying earlier about a fish needing to be very
freshly dead to give good data: it had been barely 1.5 hours since they were euthanized and there was already a notable deterioration of the tissue! The transparent tube- or worm-like structures are "mineralized tubules," an aging change in fish.
Moving on, here's a section of 2's spleen:
There are two things visible here: the same sort of granulomas caused by Mycobacterium
that we saw on the kidneys and what's called "inflammatory centers." I can't positively remember which is which, but I believe the darker ones with the harder edges are the inflammatory centers). As you can see, the damage was pretty extensive.
For contrast, here is a spleen section from '1':
He still has the inflammatory centers and granulomas, but not nearly to the extent that '2' did.
Here's a section of 1's GI tract, specifically the intestines:
The circular things you see are actually food particles that were still in his system when he was euthanized, showing that he continued to eat up until the point we put him down. As a somewhat related side note: contrary to some of the articles I'd foud in my research that suggested loss of appetite as a symptom of TB, Dr. Palmeiro says the the massive weight loss and continued appetite till death or very near death is actually quite common.
Zooming in on a different section of 1's intestines, we found a single nematode parasite:
A single parasite does not a major health problem make, so the going theory is that this single parasite did little to contribute to 1's health problems. What I didn't think to ask Dr. Palmeiro was if the fact that there was only that one parasite could be indicative as to the effectiveness of the de-parasite/worming medications you guys pointed me to earlier in this thread.
Here's a more zoomed in shot of that nematode:
If you were able to see this on the live-image of the microscope instead of this still capture, you'd be able to see that this nematode wasn't quite dead yet (still moving a little bit). In case you're curious, the mouth is on the end of the body (kind of like a worm). The histopathology should help identify exactly which type of nematode this is.
That's all for the pictures worth sharing. In my next post, I'll talk about some more of the things I learned from him about TB/Mycobacterium
and some of my brainstorming on what my strategy should be moving forward.