Mystery bichir death

[elbereth]

Hi folks. I realize I can't get an exact diagnosis but my P. senegalus died the other day with no warning and I thought maybe you could help me brainstorm some possible causes I could research further.

I've had her for around 6 or 7 years, maybe more, and she's been in a 75g tank with four other polys for most of that time. She was the most active and voracious member of that tank and the only aggressive one, so I'm sure tankmate aggression wasn't the cause of death. She was active and eating as usual the day before and there were no outward signs of disease or injury when I found her dead. Is it possible for polys to die from eating a pebble and being unable to pass it? I did notice she'd been nosing around the plants and there were a few pieces of gravel around the plant roots. But if she did die because of an obstruction, would it have happened so quickly?

I also left the tank without water changes for 4 weeks when I went on vacation but I came back 3 weeks ago and did a massive water change. But surely high nitrates couldn't have caused a sudden but delayed death like this? I admit there have been weeks before where I haven't kept up with water changes due to real life issues but my polys never seemed to show any ill effects. Is it possible that there were ill effects and they've accumulated over time?

Any ideas? I'm starting to think my other polys clubbed together to do her because they look far too happy now that she's gone!

 

[elbereth]

I'm kicking myself about the gravel now but none of my polys ever showed signs of trying to eat small pebbles that made their way into the tank so I didn't think it'd be a problem.

 

[SpecialKay]

Internal blockage, parasites, or bad genetics are a few possible causes.

Internal blockage can definitely kill a poly, especially from small indigestibles like gravel or pebbles. The danger isn't that they'll try to eat the stones, but that it'll get swallowed up accidentally along with food. I use sand as my substrate for this reason.

High nitrates for a few weeks isn't a big deal for healthy bichirs, but that can change of they have internal parasites. The nitrates can stress the fish, weakening their immune system and allowing the parasites to increase rapidly and cram the bowel system, which will kill the fish. Wild caught bichirs will tend to have them, but captive bred ones can also get them if they're fed feeder fish.

Lastly, commercially bred Senegals are extremely inbred, and more prone to various fatal health complications.

 

[elbereth]

Thanks for a very informative answer!

It was probably blockage then. She must've been commercially bred so inbreeding could've been an issue too but she seemed otherwise healthy. And I treated all my polys when I got them for parasites and never use feeder fish so that's not likely. But good to know about the link between high nitrates and parasites - I didn't know that.

Time to get all those small pebbles out of the tank.

 

[Rougarou]

While anything is possible, this doesn’t really sound like a blockage, only because the fish was behaving normally up to that point. If it was a blockage, its belly would have been noticeably distended, and it would have exhibited signs of distress. More than likely it was some sort of internal injury, or some genetic flaw it could no longer overcome.

 

[elbereth]

I would've thought a generic flaw also wouldn't cause such a sudden death but I suppose it's possible. Thank you.