Who or what is killing my fish?

[jmottle]

I'm hoping someone here can help me figure out why one species of my fish are being killed. I have a 10 gallon tank that for a year had a Giant Danio and a Zebra Danio. Two weeks ago my Giant Danio jumped out of the tank through a tiny slot where the water filter conects and he died. Over the weekend I bought a few more fish and this as of Monday was what my tank contained:

1 - Zebra Danio about 1.25" long
3 - Glass(Red Eye) Tetras (Moenkhausia oligolepis) 1.25" long
3 - Serpae Tetras (Hyphessobrycon serpae) - 0.5-1" long
1 - Golden Marble Algae Eater
1 - Drarf Frog 0.75 "long

Yesterday duing the day I found one of my Serpaes stuck up against the filter intake and he had been attacked as his eyes and inards were partially eaten. It happend in the middle of the day while I was not wathing. Today I found another one floating on the bottom with one of his eyes missing. He too looks to have been attacked. I have one left now and he is the smallest and I am worried he will be next and I want to know who is doing it. I suspect that it may be my Danio, but I'm not sure. THe Glass Testras seems to dosile and my frog and algae eater surely did not do it. Does any one have any ideas. Help!

Thanks,
Jeff

[OrionGirl]

It's unlikely that any of the fish you listed are attacking and killing other fish. It is highly likely that the new fish are stressed and in poor shape, so are dying off, and the corpse is being eaten by the remaining fish. Pretty much all fish will scavenge, given the chance.


You may want to test your water parameters--that's a pretty big increase to your bio-load, and it will take a few days for the bacteria population to accomodate the jump. You're probably going to experience a bit of a spike in ammonia and nitrites while the tank regains balance. This is not good for the fish, and may be causing the fatalities.

[jmottle]

I thought about this, but the fish all appear to be healthy. I sit right next to the tank and in the matter of 1-2 hours while I was working the fish died? Can this happen this fast. They have all been eating and swiming around quite normally.

Thanks,
Jeff

PS as an aside I have been reading about the possibility of mixup between clawed and non-clawed dwarf frogs and based upon all the tell-tale signs I do not have a clawed frog.

[OrionGirl]

Without knowing water parameters, it's impossible to say if this is ammonia toxicity, or something else. However, death from a wide number of causes can happen very quickly. If the fish were not properly acclimated to your water conditions (ie, pH, DOCs, nitrate, temp, hardness), the shock could be killing them as well.

Young fish are almost entirely made of soft tissues--very little bony areas exist until maturity. Once a fish ails, other will immediately begin nipping and harrassing. This is why it may look like a fish was killed by tankmates--and why a body is sometimes never found.