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Discussion Starter #1
A while ago, I discovered one my of white cloud minnows (WCMM) was missing his dorsal fin completely. I thought it was odd, but thought it must have been missing since I got him, since you really have to look to see that it's missing.

But the other day I noticed another one is missing his entire dorsal fin, and his other fins were a bit beat up.

So I'm trying to figure out how they're getting injured.
I've got the 10 WCMM, and 1 betta in my 15g.

I've never seen my betta chase them, but that doesn't mean he doesn't. The minnows always steal his food, and they get awfully close to his mouth in the process, though I don't see how an accidental nip could tear off the whole fin...

The filter is a stingray 15. I never noticed a huge suction on the intake, since there's a sponge right in the intake strainer. I've also put a sponge behind the filter, since one of the minnows, and the betta (!) has gotten trapped behind there before. So now nothing can get behind the filter.

There are 3 "boss" minnows. These are 3 of my 5 original minnows. So they're bigger than the newer ones.

Other than that, I've just got the usual things in the tank, heater, thermometer, rocks, a few plants, and sand for substrate.

So what could be injuring the minnows? The betta? Another minnow? The filter?

On the first guy I noticed missing, he's otherwise totally normal, though the fin never grew back. Doesn't affect his swimming at all that I've noticed. Actually, it's kind of funny when he flares at the other minnows, since he doesn't have his dorsal to stick up, the others just ignore him :p
 

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Wow! You are having a run of the most interesting and perplexing problems! It's too bad that you're having these issues with your bettas, tetra and minnows, but on the other hand, you're making us stretch our brains.

I'm sorry to hear that your minnows are losing their fins. My first question would be, is the betta that's in the tank with the minnows, a betta that is (or has been) sick? If the betta is one that you've had to treat lately, then I might suspect some kind of infection. If the betta has been healthy all along, then I think that this is the betta's way of asking for his own tank.

Good luck!
 

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Hi, I've never seen that kind of aggression between my white clouds, regular or long fin. Also, while it's possible they could be getting damaged in the filter intake, they are river fish, and pretty strong swimmers. Even my fry don't have any difficulty swimming 'round the filter intake.
Bettas get irritable;constant nipping and the occasional lucky bite will do damage. Like you said, that dorsal flares, and make a pretty tempting target.
 

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Discussion Starter #4
I know Morainy -.-' It all happens at once too... All will be well, then boom! 5 different things at once!

The betta (Enigma) is the one who currently has a mysterious grey spot on the side of his head. So far, just added a wee bit of salt to the tank (just 2 tsp for the 15g) but I will up the concentration when I do the water change tomorrow.

I should mention that the first minnow missing his fin and this new one were months apart, so I don't think it's any sort of infection.
But I had an oto die in the same tank recently...

Enigma probably is the most likely suspect, though I've never seen him show any sort of interest toward the minnows. Mind you, I never saw him show any interest in the shrimp either, but now I don't have any shrimp :p
 
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